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Prone position breast irradiation
Int. J. Radiation
Oncology
Pergamon
Biol. Phys.. Vol. 30, No. I, pp. 197-203. 1994 Copyright 0 1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0360-3016/94 $6.00 + .OO
0360-3016(94)E0225-9
??Technical Innovations and Notes
PRONE POSITION BREAST IRRADIATION THOMAS E. MERCHANT, Department
of Radiation
Oncology,
Memorial
D.O.,
PH.D.
Sloan-Kettering
AND BERYL MCCORMICK, Cancer Center,
M.D.
1275 York Ave., New York, NY 1002 1
Purpose: An alternative technique for irradiating the breast following breast conserving surgery is described. Methods and Materials: The technique utilizes the prone position and has been developed to improve the dose distribution within the breast and reduce the volume of normal tissues irradiated during whole breast treatment. Improvements in the dosimetry of breast irradiation are obtained through the optimization of the shape of the breast and result in a reduction in the magnitude of high-dose regions and isodose gradients at the base of the breast. Results: The high dose region at the base of the breast, without lung correction, generally ranges from 116-l 18% for large breasted women treated in the supine position. These high dose regions are reduced to 102-103% for the same women treated1 in the prone position. Irradiation of the heart, lungs, chest wall and contralateral breast are minimized with this technique. The improvements appear to benefit women with large breasts, pendulous breasts, large separations and/or irregularly shaped chest contours. Conclusion: The prone position technique takes advantage of the reproducibility characteristics of the supine position technique and combines them with the homogeneity and normal tissue-sparing characteristics of the lateral decubitus position technique. Prone position breast irradiation appears to be a simple and effective alternative to irradiation of the breast in the conventional supine position when the supine position is likely to result in unacceptable dose inhomogeneity or significant doses to normal tissues. Breast irradiation, Breast cancer, Radiation therapy, Breast, Radiotherapy.
INTRODUCTION
Optimal radiotherapy technique is described as 45-50 Gy to the whole breast over a period of 4.5-5 weeks, followed by a boost to the excisional biopsy site with an additional lo- 15 Gy. The technical aspects of delivering radiation therapy as a part of breast conserving therapy are less well-defined and have evolved as a function of technical innovation and studies examining the patterns of failure. Improvements in methods for field matching ( 12, 23), the abandonment of routine regional nodal irradiation, and controversies concerning the necessity and method for boost treatment, sequencing of chemotherapy, and indications for radiation therapy, appear to distract the radiation oncologist from attempting technical improvements in the delivery of radiation therapy. Treatment simulation and set-up are carried out primarily with the patient in the supine position, although certain centers continue to use the decubitus position as their standard treatment position. When patients with large breasts are encountered, the decubitus position is sometimes used as an alternative. While the supine position is considered more reproducible, it irradiates more lung and requires the use of wedge filters to overcome nonhomogeneous dose distributions. The decubitus tech-
The acute toxicity, long-term side effects, and cosmetic outcome observed in patients treated with radiation therapy following breast conserving surgery can be attributed to a number factors. These factors include the technical aspects of surgery (7, IS), preexisting collagen vascular disease that may be a contraindication for radiation therapy (8). the use of specific chemotherapeutic agents and their administration relative to the delivery of radiation therapy (7,20), radiation therapy treatment technique (7, 13, 18, 19) and patient morphology (I 1). While the radiation oncologist can influence the sequencing of chemotherapy and optimize the delivery of radiation therapy, certain factors, namely surgical and patient morphology related, known to be responsible for increasing the toxicity of treatment and the likelthood of a poor cosmetic outcome, are beyond the influence of the radiation oncologist. The technical aspects of surgery rely solely on the experience of the surgeon and patient morphology. Large or irregular patient shape is a factor in radiation therapy treatment planning and one which results in a less favorable cosmetic outcome.
Accepted
Reprint requests to: Thomas E. Merchant, D.O., Ph.D. ilLknoMJk~d~ements_The authors wish to acknowledge the technical contributions of Ricardo Govantes and Karl Pfaff. 197
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nique is performed with the breast tissue compressed to an even thickness of 6-8 cm and results in a more homogenous dose distribution. The decubitus technique requires meticulous positioning and protection of the contralateral breast; it is, however, considered less reproducible and lacks the flexibility of supine position treatment, especially when nodal irradiation is considered (27). For these reasons, the decubitus technique is seldom used and has dropped from favor (4). Women with large, pendulous breasts, or women with abnormal chest wall contours can have large medial to lateral separations exceeding 23 cm; these women require a modification or alternative to the traditional treatment techniques. When treatment is carried out in the supine position, the transverse displacement of breast tissue over the anterior chest wall creates a large separation resulting in nonuniformity in the dose distribution and the irradiation of large volumes of lung and heart. A number of technical modifications have been proposed to improve the dose distribution in women with large separations. These modifications include the use of wedge filters, highenergy photon beams, beam-spoilers, and bolus (17, 24, 25). We propose using the prone position and a prototype platform to overcome the limitations of treating women with large breast separations. This technique combines the advantages of decubitus position treatment and the reproducibility of supine position treatment with the several notable advantages. The technical aspects of the prone position treatment will be described and discussed along with the indications for this type of treatment technique.
METHODS
AND
MATERIALS
The objectives of the prone technique are to orient the patient in a position for breast irradiation using lateralopposed tangential photon beams, optimize the shape of the breast with regard to the chest wall for treatment, and minimize the volume of normal tissue within the radiation therapy portal. Treatment of the breast only is described in the present report. The patient lies prone on a platform (Fig. 1). This platform can be mounted on both a simulator couch and an accelerator treatment table; our prototypes consist of a flat or curved bed containing an aperture through which the breast hangs in a dependent fashion. The aperture may consist of a hole in the platform or a slot, allowing the entire breast and a portion of the chest wall to hang away from the thorax. The medial and lateral borders of the breast tissue, determined clinically, must be included within the field of the tangential parallel-opposed photon beams. Arm position is important as it can enhance patient comfort and assure reproducibility and treatment of the entire breast. The ipsilateral arm may be placed either at the side or above the head. The contralateral arm position depends more on the type of platform used. Simulation and treatment planning involve many of
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b
Fig. 1. Patient positioned for breast irradiation in the prone position. The platform used in this example consists of an opening in the platform top through which the treated breast hangs dependently along with a portion of the ipsilateral chest wall.
the steps normally required for the simulation of a patient for supine breast treatment. These steps include patient immobilization, selection of the optimal aperture size to allow for the breast and chest wall to hang below the level of the platform, the simulation of tangential beams with isocentric techniques, and tattoos placed at the field edges on the chest wall laterally and medially. A transverse contour is taken at the level of the medial and lateral field centers with the patient in the treatment position. With the patient in the prone position, calculating the angle of divergence (6) for the tangent fields, whose edge of intersection is horizontal, requires only knowledge of the field width. The divergence and medial and lateral angles of the tangential fields are calculated as follows: 6 = arctan (W/200), where W = field width; left breast: medial angle = 270 - 6, lateral angle = 90 + 6; right breast: medial angle = 90 + 6, lateral angle = 270 - 6. The value of 6 is approximately 6” for field sizes of 20 X
Breast irradiation ?? T.E. MERCHANT
20 cm. It is not necessary to determine the breast bridge a maneuver normally used to calculate the medial and lateral angles. The treatment platform itself is relatively simple; however, certain design specifications are critical. The vertical specifications of the platform, that is, the elevation of the platform above the treatment table, depend on the maximal distance that a large or pendulous breast might hang. We have determined that a clearance of 30 cm is sufficient for the majority of patients. It should be noted that the top of the treatment table c’n most linear accelerators cannot be elevated sufficiently lo cover the entire breast. Thus, modification of the existing accelerator treatment table may not allow the patient to be treated in this position without an elevated platform. A number of prototype platforms have been used for this study to date. In general, they involve a flat or curved surface and an adjustable circular, ovoid or slit aperture for the breast and chest wall. The initial prototype platform limited our ability to image the chest wall at the base of the breast and verify the treatment position with plain film radiographs. These problems with vertical positioning have been overcome with the development of a second prototype whose aperture consists of a simple slit that can be opened or closed to accommodate the patient’s breast size, and allows the treated breast to be comfortably positioned, palpated, radiographed, and tattooed. It should be noted that stairs are required to assist the patient in climbing onto the platform since the platform substantially elevates the treatment surface. The width of the treatment platform is determined by the width of the accelerator treatment table. In this study, to obtain an isocenter at 100 cm, the block tray accessory of the accelerator head had to be removed for treatment on our linear accelerator.’ The cranial-caudal dimensions of the breast require that the aperture and supportive elements of the platform allow for a variable field size of 1530 cm. Verification of treatment requires that portal films be taken and compared with plain films taken at the time of simulation (Fig. 2). The ribs are the most reliable radiographic landmark and provide the radiation oncologist with knowledge of the amount of chest wall, lung, and heart that fall within the treatment portals. Limitations of the prone position treatment are patient related. Large breasted women are often obese and have difficulty climbing on to the platform and lying prone as do older women. Obese individuals may also have excess nonmammary soft tissue that hangs in the treatment portal when the aperture is not properly optimized and at times requiring additional immobilization with aquaplast* or alpha-cradle’ material.
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angle,
’ Varian Clinac 6OOC, Palo Alto, CA. * Aqua-plast Corp., Wyckoff, NJ.
Fig. 2. Lateral simulation radiograph of a patient in the prone breast treatment position. The posterior field edge includes chestwall and the remainder of the breast hangs dependently through a slit aperture in the treatment platform.
RESULTS Representative isodose distributions are presented for a patient simulated in the supine and prone positions (Fig. 3). These isodose distributions are calculated for the transverse contours of the breast through the isocenter. The uniformity of the isodose distribution has been optimized in the transverse plane for both techniques through the use of field wedges. In the case of the supine treatment, the field wedges consist of mixture of 15” and 30” wedges. A combination of 15” and 30” wedges would be exchanged during the treatment course. The prone treatment requires only the use of half-field wedges which remain throughout the course of treatment. The supine isodose distribution, normalized to the chest wall interface, is characterized by a high-dose region at the apex of the breast (104% isodose) and at the periphery of the breast (116% isodose). Treatment in the prone position results in high dose regions at the apex (104%) and base (103%) that are considerable less than those of the supine position. In addition, the dose gradient across the breast is substantially reduced. We have found in general that the high dose region at the base of the breast ranges from 116- 118% for large breasted women treated in the supine position to 102- 103% for the same women treated in the prone position. Normalization of the isodose distribution is generally performed at the chest wall interface. If corrections are actually made for the volume of lung appearing in the treatment portal ofthe supine technique, the percent isodose of the high-dose regions is increased. In Figure 3 an example of corrected and uncorrected
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Fig. 3. Isodose distributions for breast treatments carried out in the prone and supine positions with transverse contours taken at the center of the treatment field. The prone position isodose
distribution (top), supine position isodose distribution (bottom) are presented with a supine position isodose distribution (right) corrected for lung transverse by the treatment field.
isodose distributions in the supine position are presented. Correction for lung within the treatment portal with normalization at the same point results in a 10% increase in the peripheral high-dose region. For breasts treated in the prone position, the selection of a reference point for normalization becomes critical in determining the magnitude of the high-dose regions. In the case of the isodose distributions presented in Figure 3, the breast-chest wall interface was selected for normalization based upon radiographic verification of the breast-chest wall interface.
Can radiation physics
DISCUSSION Although the present methods used to deliver radiation therapy to the breast result in excellent local control and cosmesis in a majority of patients, further optimization of breast radiotherapy may be possible by improving dose uniformity and reducing the dose received by normal tissues. The technique of prone position breast irradiation offers a simple and effective alternative to irradiation of the breast in the supine position when the supine position treatment is likely to result in substantial isodose nonuniformities or significant doses to the lung or heart. While the size of the breast, location of the primary tumor, and the volume of tissue removed at the time of surgery play an important role in predicting cosmetic outcome (7, 18,26) patients with large, pendulous breasts or large separations, are less likely to achieve an excellent cosmetic outcome and are more likely to suffer the side effects of dose inhomogeneities. Thus, patients with large breasts are among the group of patients most likely to gain from efforts to improve the dose distribution within the breast.
qfthe breast be improved?
There are a number of techniques that can be used to shape the distribution of dose within the breast. Slessinger et al. (24) investigated the use of a Lucite beam spoiler or layer bolus to achieve the dose buildup characteristics of 6-MV tangential photon beams for patients with large breasts treated with 18-MV photons. Using a Lucite beam spoiler suspended 13.5 cm proximal to the isocenter, a surface dose with 18-MV photons was achieved which. was within 8% of that obtained with 6-MV photons. At a depth of 3.5 mm, however, the dose with 18-MV photons was 16% lower than that obtained with 6-MV photons. At greater depths, the dose with 18-MV photons differed, on average, 10% with the dose obtained using 6MV photons. In a separate experiment, these authors found that the use of 5 mm super flab layer bolus with 18-MV photons increased the surface dose by 23% compared with 6-MV photons, however, from depths of 3.512.5 mm, the dose was within 7% of that obtained with 6-MV photons. Muller-Runkel et al. (17) investigated the use of 18-MV photons or mixed beams of 6- and 18MV photons to improve the dose homogeneity within the breast. Although the homogeneity was improved with this method, treatment breaks were required in a number of patients. Wedges are the most common beam modifier used to improve dose uniformity. The improvement in the isodose distribution, however, can only be analyzed in the plane from which a contour has been taken and contours are generally limited to the isocenter in the transverse plane. This practice neglects the assessment of dose inhomogeneities in other planes. It also accounts for the limitation of wedges that stems from the need to have the beam modified in additional planes to compensate for surface
Breast irradiation 0 T. E.
slope and other tissue irregularities. Wedges are often used only for a portion of the treatment and, unless used in a dynamic fashion, may lead to additional uncertainties in the estimated isodose distribution. From our limited experience with the prone position technique, and through the comparison of isodose distributions determined from the contours of large breasted women simulated in both the supine and prone positions, an improvement in dose uniformity and a reduction in the dose to normal tissues has been achieved (Fig. 3). The gradient of dose at the base of the breast is reduced in the prone position. The dose gradient from the apex of the breast to its base at the chest wall interface is also reduced in the prone position. The dose gradients calculated from contours of breasts in the supine position are actually underestimated since corrections for lung, normally present in the radiation portal at the base of the breast, are not included in the isodose calculations. When a patient is treated in the prone positia’n, the volume of lung included in the radiation portal is either nonexistent or too small to require a correction. This claim requires verification using computed tomography. If the lung volume in the prone position is small or nonexistent, the isodose gradients, described for the breast treated in the prone position, are a realistic representation of dose deposited in an approximate cylinder ‘of tissue. Ordinarily, the dose distribution for any patient treated in the supine position is depicted using a contour of the patient’s axial anatomy at the center of the breast. This practice ignores the patient’s axial contours at the most extreme cranial and caudal levels, as well as prone the sagittal dose distribution which, through the center, would include the extreme cranial and caudal aspects of the breast. When the breast is treated in the prone position, as the breast hangs dependently to form an imperfect cylinder, the axial contour and dose distribution, like those presented in this study, are more representative elf the dose distribution in the sagittal plane. This is especially true when pendulous breasts with large inframammary folds are encountered. The same approximate cylindrical symmetry for the isodose distribution cannoi. be achieved for breasts treated in the supine position since the breast can take many forms in the sagittal plane. The marked difference between transverse and sagittal dose distributions was previously described by Svensson et al. (25).
What are the implications
qf improved dose uniformity
Good to excellent cosmetic results can be achieved in SO-90% of patients treated with meticulous surgery and radiotherapy techniques. Even with careful radiotherapy, which limits whole-breast and boost doses to those levels known to result in excellent cosmesis and local control, the risk of breast fibrosis, soft tissue necrosis and rib fractures remain measurable (19, 26). With the use of concurrent chemotherapy, there is an increased incidence of acute skin toxicity (7, 20). The risks of side effects are
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further amplified in women with large or pendulous breasts who are less likely to achieve excellent cosmetic results because of nonuniformities in the dose distribution. Pierce et al. ( 19) evaluated the long-term complications of radiation therapy in patients with early stage breast cancer treated with breast conserving surgery. In their analysis of 1624 patients followed for a median of 79 months, the incidence of rib fractures differed significantly between 4 and 6- or 8-MV accelerators (0.4 vs. 2.2%) and whole breast dose of 45 Gy or less and 45-50 Gy (1.4% vs. 5.7%) treated using 4-MV photons. They noted an 0.18% rate of soft tissue necrosis requiring surgical correction. Although these authors did not mention the rate incidence of poor cosmetic outcome due to fibrosis, Van the influence of total Limbergen et al. (26) investigated dose, fractionation and surgery on cosmetic outcome in 142 patients analyzed for cosmetic outcome, asymmetry and retraction due to fibrosis. They discovered that when the dose to the breast exceeded 75 Gy, the incidence of poor cosmetic outcome exceeded 30%. They quantified fibrosis and determined that a dose response occurred for total doses between 40 and 86 Gy when the fraction sizes exceeded 2 Gy. For each additional 1 Gy above 50 Gy, a linear displacement in the nipple and loss of breast contour could be measured. Their findings also revealed that segmentectomy compared to tumorectomy, en bloc compared to separate incisions and nodal irradiation compared to the use of tangents only, were associated with a significantly high risk of poor cosmetic outcome. Treatment complications such as fibrosis, rib fractures, and soft tissue necrosis result from areas of dose inhomogeneity that result in high-dose regions or gradients. In the acute setting, dose inhomogeneities lead to the skin reactions that are noted in the periphery of the breast when the patient, treated in the supine position, approaches the completion of whole breast radiotherapy.
What are the implications volumes?
qf reduced normal tissue
There are a number of reported experiences that assess the risks associated with the irradiation of normal tissue structures as a part of breast conserving surgery and adjuvant radiation therapy. There is also a body of evidence that implicates radiation therapy to the breast as less than innocuous. This makes optimization of radiotherapy techniques and the reduction in dose to normal tissue volumes even more important (22). Roberson et al. (2 1) calculated dose-volume curves using anatomic data derived from CT scans of the chest with patients in the supine treatment position. Their curves show that 22% of the ipsilateral lung receives at least 85% of the total dose using standard tangents (medial entrance 3 cm beyond midline and lateral entrance point 1 cm below palpable breast marked clinically) and approximately 38% of the ipsilateral lung receives at least 85% of the total dose when using deep tangents (fields
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moved parallel to standard tangents until the entire sternum is in the field). The risk of symptomatic pneumonitis, pericarditis and second primary tumors as a result of radiation therapy have been determined by a number of groups. According to Lingos et al. (19) when tangential fields are used alone, pneumonitis occurs in 1.0% of patients. They also described pneumonitis as being correlated with the use of chemotherapy and occurring independent of the volume of lung treated, although their range of volumes was limited and not directly measured. Pierce et al. (19) also showed that pericarditis occurred in 0.4% (3/831) of women treated with left breast irradiation and that chest wall sarcomas developed in 0.18% (3/ 1624) of women treated with breast radiotherapy. Boice et al. ( 1) concluded that the risk of radiationinduced contralateral breast cancer is small and not a consideration for selecting treatment. Curtis et al. (5) stated that the relative risk of leukemia following breast irradiation was 2.4% and depended on the volume of bone marrow irradiated. Techniques which further reduce the volume of chest wall irradiated as a part of adjuvant breast radiotherapy may have an impact on these statistics (6). The prone position method reduces the volume of lung, heart, and chest wall in the radiation therapy portal. Furthermore, the prone position breast treatment reduces the dose to the contralateral breast by several mechanisms as described by Frass et al. (10): (a) When the breast hangs in a dependent fashion away from the chest wall, the volume of chest wall that requires treatment with tangential fields is reduced and subsequently, a substantial amount of internal scatter; (b) The prone position treatment does not require the use of blocking material which can result in a nonalignment of beam edges and increase the dose to the opposite breast; (c) The treatment platform can be designed to include additional shielding materials and reduce the perpendicular distance of the contralateral breast from the field edge; (d) Wedges are either not required or their angle is reduced with the prone technique, therefore, fewer monitor units are necessary to overcome beam attenuation by the wedges. In spite of the fact that considerable work has been performed to determine ways to minimize the dose to normal structures and to determine the symptomatic acute and long-term side effects of treatment, the asymptomatic functional deficits, which may manifest themselves clinically in other forms of morbidity, await evaluation using functional imaging techniques such as SPECT to measure flow in irradiated lung ( 14).
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What are the negative ramifications of prone position breast irradiation? From a technological standpoint, it is apparent that nodal irradiation is not practical with this technique. This does not diminish the value of the technique since there are many large breasted women with node-negative invasive breast cancer or ductal carcinoma in situ who could benefit from the use of the prone technique. From an oncologic point of view, a smaller amount of chest wall is irradiated when compared to the supine position. The location of breast tissue with respect to the chest wall, with the patient in the supine position, has been verified by magnetic resonance imaging (MRI) studies (15, 16) performed in the prone position. Magnetic resonance imaging has been used to improve breast surgery treatment planning ( 15) and may help to select patients for the prone position treatment and define a subset of patients in whom irradiation of the entire chest wall using the horizontally opposed tangential fields is required. Fowble et al. (9) show that there was no difference in the patterns of failure, or 5-year actuarial, relapse-free and NED survival in 886 patients with Stage I and II breast cancer analyzed according to the site of the primary disease in the breast. Although patients were treated in the supine position for that series, the experience of the Curie Institute, using breast conserving surgery and adjuvant radiation therapy performed in the decubitus position, supports the use of the prone position as an alternative technique for breast irradiation. Calle et al. (2, 3) reported the IO-year results from the Curie Institute as 90% (290/324) NED survival at 5 years and 8 1% ( 140/ 173) NED survival at 10 years. Mammary and axillary recurrences were reported to be 8% at 5 years and 10% at 10 years with the majority of recurrences occurring at the tumorectomy site. Prone position irradiation of the breast is a feasible alternative to supine position treatment for patients with large medial to lateral separations or other morphological aspects that result in nonuniform isodose distributions when treated in the supine position. Improving the dose distribution throughout the breast may prove beneficial in increasing the tolerability of concomitant chemotherapy by reducing the risk of acute and long-term side effects. The reduction in the volume of normal tissue irradiated with this technique has the potential to benefit women with preexisting pulmonary or cardiac diseases undergoing breast conserving therapy. Large breasted women appear to benefit most from this treatment, although women of all sizes may benefit once additional verification of the technique and a comparison of normal tissue volumes is carried out using computed tomography.
REFERENCES 1. Boice, J. D.; Harvey, E. B.; Blettner, M. Cancer in the breast after radiotherapy for breast cancer. N. Engl. J. Med. 326: 781-785; 1992. 2. Calle, R. Primary breast cancer: European radiotherapy trials. Clin. Trials Cancer Med. 8: 123-l 36; 1985.
3. Calle, R.; Pilleron, J. P.; Schlienger, P.; Vilcoq, J. R. Conservative management of operable breast cancer. Ten years experience at the foundation curie. Cancer 42:2045-2053; 1978. 4. Cross, M. A.; Elson, H. R.; Aron, B. S. Breast conservation
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radiation therapy technique for women with large breasts. Int. J. Radiat. Oncol. Biol. Phys. 17: 199-203; 1989. Curtis, R. E.; Boice, J. D.; Stovall, M. Risk of leukemia after chemotherapy and radiation treatment for breast cancer. N. Engl. J. Med. 326: 174.5-175 1; 1992. DeLaney, T. F.; Pierce, Id. J. Cancer in the contralateral breast after radiotherapy for breast cancer. N. Eng. J. Med. 327:430; 1992. de la Rochfordiere, A.; Abner, A. L.; Silver, B.; Vicini, F.; Recht, A.; Harris, J. R. Are cosmetic results following conservative surgery and radiation therapy for early breast cancer dependent on technique? Int. J. Radiat. Oncol. Biol. Phys. 23:925-93 1; 1992. Fleck, R.; McNeese, M. D.; Ellerbroek, N. A.; Hunter, T. A.; Holmes, F. A. Consequences of breast irradiation in patients with preexisting collagen vascular diseases. Int. J. Radiat. Oncol. Biol. Phys. 17829-833; 1989. Fowble, B.; Solin, L. J.; Schultz, D. J.; Weiss, M. C. Breast recurrence and survival related to primary tumor location in patients undergoing conservative surgery and radiation for early stage breast cancer. Int. J. Radiat. Oncol. Biol. Phys. 23:933-939; 1992. Frass, B. A.; Roberson, F’. L.; Lichter, A. S. Dose to the contralateral breast due to primary breast irradiation. Int. J. Radiat. Oncol. Biol. Phys. 11:485-497; 1985. Gray, J. R.; McCormick, 13.;Cox, L.; Yahalom, J. Primary breast irradiation in large-breasted or heavy women: Analysis of cosmetic outcome. Int. J. Radiat. Oncol. Biol. Phys. 21: 347-354; 1991. Hunt, M. A.; Kutcher, G. J.; Martel, M. K. Matchline dosimetry of a three field technique for breast treatment using cobalt or 6-MV X rays. Int. J. Radiat. Oncol. Biol. Phys. 13:1099-l 106; 1987. Lingos, T. I.; Recht, A.; Vicini, F.; Abner, A.; Silver, B.; Harris, J. R. Radiation pneumonitis in breast cancer patients treated with conservative surgery and radiation therapy. Int. J. Radiat. Oncol. Biol. Phys. 21:355-360; 1991. Marks, L; Sontag, M; Spencer, D.; Ray, S; Antoine, P; Sherouse, G; Bentel, G; Coleman, R. E.; Jasczak, R.; Tapson, V.; Prosnitz, L. Three dimensional SPECT lung perfusion scans in designing radiation beams and in predicting and assessing the physiological consequences of thoracic irradiation (Abstract 191). Int. J. Radiat. Oncol. Biol. Phys. 24: 238; 1992. Merchant, T. E.; Obertop, H.; de Graaf, P. W. Advantages of magnetic resonance imaging in breast surgery treatment planning. Breast Cancer Res. Treat. 25:257-264; 1993. Merchant, T. E.; Thelissen, G. R. P.; Kievit, H. C. E.; Oosterwaal, L. J. M. P.; Bakker, C. J. G.; de Graaf, P. W. Breast disease evaluation with fat-suppressed magnetic resonance imaging. Magn. Reson. Imag. 10:335-340; 1992.
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17. Muller-Runkel, R.; Kalokhe, U. P.; Schreiber, G. Radiation therapy of unusually large breasts: Using higer energy photons with or without bolus for all or part of the treatment course. Poster 1070, ASTRO 1991. 18. Olivotto, I. A.; Rose, M. A.; Osteen, R. T.; Love, S.; Cady, B.; Silver, B.; Recht, A.; Harris, J. R. Late cosmetic outcome after conservative surgery and radiotherapy: Analysis of causes of cosmetic failure. Int. J. Radiat. Oncol. Biol. Phys. 171747-753; 1989. 19. Pierce, S. M.; Recht, A.; Lingos, T. I.; Abner, A.; Vicini, F.; Silver, B.; Herzog, A.; Harris, J. R. Long-term radiation complications following conservative surgery (CS) and radition therapy in patients with early stage breast cancer. Int. J. Radiat. Oncol. Biol. Phys. 23:915-923; 1992. 20. Ray, G. R.; Fish, V. J.; Marmor, J. B.; Rogoway, W.; KushIan, P.; Arnold, C.; Lee, R. H.; Marzoni, F. Impact of adjuvant chemotherapy on cosmesis and complications in Stages I and II carcinoma of the breast treated by biopsy and radiation therapy. Int. J. Radiat. Oncol. Biol. Phys. 10: 837-841; 1984. 21. Roberson, P. L.; Lichter, A. S.; Bodner, A.; Fredrickson, H. A.; Padikal, T. N.; Kelly, B. A.; van de Geijn, J. Dose to lung in primary irradiation. Int. J. Radiat. Oncol. Biol. Phys. 9:97-102; 1982. 22. Rotstein, S; Lax, 1.; Svane, G. Influence of radiation therapy on the lung tissue in breast cancer patients: CT-assessed density changes and associated symptoms. Int. J. Radiat. Oncol. Biol. Phys. 18:173-180; 1990. 23. Siddon, R. L.; Buck, B. A.; Harris, J. R.; Svensson, G. K. Three-field technique for breast irradiation using tangential corner blocks. Int. J. Radiat. Oncol. Biol. Phys. 9:583-588; 1983. 24. Slessinger, E. D.; Devineni, V. R.; Lewis, P. Early breast cancer: Duplication of 6-MV dose buildup with 18-MV X rays in patients with large separations (Abstract 1095). Int. J. Radiat. Oncol. Biol. Phys. 24:295; 1992. 25. Svensson, G. K.; Siddon, R. L.; Chin, L. M.; Harris, J. R. Breast treatment techniques at the Joint Center for Radiation Therapy. In: Harris, J. R., Hellman, S., Silen, W., eds. Conservative management of breast cancer. 239-257. 26. Van Limbergen, E.; Rijnders, A.; van der Schueren, E.; Lerut, T.; Christiaens, R. Cosmetic evaluation of breast conserving treatment for mammary cancer. 2. A quantitative analysis of the influence of radiation dose, fractionation schedules and surgical treatment techniques on cosmetic results. Radiother. Oncol. 16:253-267; 1989. 27. Vilcoq, J. R.; Calle, R.; Schlienger, P. Irradiation techniques for conservative treatment of localized breast cancer. In: Harris, J. R., Hellman, S., Silen, W., eds. Conservative management of breast cancer. 2 13-224.
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Biol. Phys.. Vol. 30, No. I, pp. 197-203. 1994 Copyright 0 1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0360-3016/94 $6.00 + .OO
0360-3016(94)E0225-9
??Technical Innovations and Notes
PRONE POSITION BREAST IRRADIATION THOMAS E. MERCHANT, Department
of Radiation
Oncology,
Memorial
D.O.,
PH.D.
Sloan-Kettering
AND BERYL MCCORMICK, Cancer Center,
M.D.
1275 York Ave., New York, NY 1002 1
Purpose: An alternative technique for irradiating the breast following breast conserving surgery is described. Methods and Materials: The technique utilizes the prone position and has been developed to improve the dose distribution within the breast and reduce the volume of normal tissues irradiated during whole breast treatment. Improvements in the dosimetry of breast irradiation are obtained through the optimization of the shape of the breast and result in a reduction in the magnitude of high-dose regions and isodose gradients at the base of the breast. Results: The high dose region at the base of the breast, without lung correction, generally ranges from 116-l 18% for large breasted women treated in the supine position. These high dose regions are reduced to 102-103% for the same women treated1 in the prone position. Irradiation of the heart, lungs, chest wall and contralateral breast are minimized with this technique. The improvements appear to benefit women with large breasts, pendulous breasts, large separations and/or irregularly shaped chest contours. Conclusion: The prone position technique takes advantage of the reproducibility characteristics of the supine position technique and combines them with the homogeneity and normal tissue-sparing characteristics of the lateral decubitus position technique. Prone position breast irradiation appears to be a simple and effective alternative to irradiation of the breast in the conventional supine position when the supine position is likely to result in unacceptable dose inhomogeneity or significant doses to normal tissues. Breast irradiation, Breast cancer, Radiation therapy, Breast, Radiotherapy.
INTRODUCTION
Optimal radiotherapy technique is described as 45-50 Gy to the whole breast over a period of 4.5-5 weeks, followed by a boost to the excisional biopsy site with an additional lo- 15 Gy. The technical aspects of delivering radiation therapy as a part of breast conserving therapy are less well-defined and have evolved as a function of technical innovation and studies examining the patterns of failure. Improvements in methods for field matching ( 12, 23), the abandonment of routine regional nodal irradiation, and controversies concerning the necessity and method for boost treatment, sequencing of chemotherapy, and indications for radiation therapy, appear to distract the radiation oncologist from attempting technical improvements in the delivery of radiation therapy. Treatment simulation and set-up are carried out primarily with the patient in the supine position, although certain centers continue to use the decubitus position as their standard treatment position. When patients with large breasts are encountered, the decubitus position is sometimes used as an alternative. While the supine position is considered more reproducible, it irradiates more lung and requires the use of wedge filters to overcome nonhomogeneous dose distributions. The decubitus tech-
The acute toxicity, long-term side effects, and cosmetic outcome observed in patients treated with radiation therapy following breast conserving surgery can be attributed to a number factors. These factors include the technical aspects of surgery (7, IS), preexisting collagen vascular disease that may be a contraindication for radiation therapy (8). the use of specific chemotherapeutic agents and their administration relative to the delivery of radiation therapy (7,20), radiation therapy treatment technique (7, 13, 18, 19) and patient morphology (I 1). While the radiation oncologist can influence the sequencing of chemotherapy and optimize the delivery of radiation therapy, certain factors, namely surgical and patient morphology related, known to be responsible for increasing the toxicity of treatment and the likelthood of a poor cosmetic outcome, are beyond the influence of the radiation oncologist. The technical aspects of surgery rely solely on the experience of the surgeon and patient morphology. Large or irregular patient shape is a factor in radiation therapy treatment planning and one which results in a less favorable cosmetic outcome.
Accepted
Reprint requests to: Thomas E. Merchant, D.O., Ph.D. ilLknoMJk~d~ements_The authors wish to acknowledge the technical contributions of Ricardo Govantes and Karl Pfaff. 197
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nique is performed with the breast tissue compressed to an even thickness of 6-8 cm and results in a more homogenous dose distribution. The decubitus technique requires meticulous positioning and protection of the contralateral breast; it is, however, considered less reproducible and lacks the flexibility of supine position treatment, especially when nodal irradiation is considered (27). For these reasons, the decubitus technique is seldom used and has dropped from favor (4). Women with large, pendulous breasts, or women with abnormal chest wall contours can have large medial to lateral separations exceeding 23 cm; these women require a modification or alternative to the traditional treatment techniques. When treatment is carried out in the supine position, the transverse displacement of breast tissue over the anterior chest wall creates a large separation resulting in nonuniformity in the dose distribution and the irradiation of large volumes of lung and heart. A number of technical modifications have been proposed to improve the dose distribution in women with large separations. These modifications include the use of wedge filters, highenergy photon beams, beam-spoilers, and bolus (17, 24, 25). We propose using the prone position and a prototype platform to overcome the limitations of treating women with large breast separations. This technique combines the advantages of decubitus position treatment and the reproducibility of supine position treatment with the several notable advantages. The technical aspects of the prone position treatment will be described and discussed along with the indications for this type of treatment technique.
METHODS
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MATERIALS
The objectives of the prone technique are to orient the patient in a position for breast irradiation using lateralopposed tangential photon beams, optimize the shape of the breast with regard to the chest wall for treatment, and minimize the volume of normal tissue within the radiation therapy portal. Treatment of the breast only is described in the present report. The patient lies prone on a platform (Fig. 1). This platform can be mounted on both a simulator couch and an accelerator treatment table; our prototypes consist of a flat or curved bed containing an aperture through which the breast hangs in a dependent fashion. The aperture may consist of a hole in the platform or a slot, allowing the entire breast and a portion of the chest wall to hang away from the thorax. The medial and lateral borders of the breast tissue, determined clinically, must be included within the field of the tangential parallel-opposed photon beams. Arm position is important as it can enhance patient comfort and assure reproducibility and treatment of the entire breast. The ipsilateral arm may be placed either at the side or above the head. The contralateral arm position depends more on the type of platform used. Simulation and treatment planning involve many of
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Fig. 1. Patient positioned for breast irradiation in the prone position. The platform used in this example consists of an opening in the platform top through which the treated breast hangs dependently along with a portion of the ipsilateral chest wall.
the steps normally required for the simulation of a patient for supine breast treatment. These steps include patient immobilization, selection of the optimal aperture size to allow for the breast and chest wall to hang below the level of the platform, the simulation of tangential beams with isocentric techniques, and tattoos placed at the field edges on the chest wall laterally and medially. A transverse contour is taken at the level of the medial and lateral field centers with the patient in the treatment position. With the patient in the prone position, calculating the angle of divergence (6) for the tangent fields, whose edge of intersection is horizontal, requires only knowledge of the field width. The divergence and medial and lateral angles of the tangential fields are calculated as follows: 6 = arctan (W/200), where W = field width; left breast: medial angle = 270 - 6, lateral angle = 90 + 6; right breast: medial angle = 90 + 6, lateral angle = 270 - 6. The value of 6 is approximately 6” for field sizes of 20 X
Breast irradiation ?? T.E. MERCHANT
20 cm. It is not necessary to determine the breast bridge a maneuver normally used to calculate the medial and lateral angles. The treatment platform itself is relatively simple; however, certain design specifications are critical. The vertical specifications of the platform, that is, the elevation of the platform above the treatment table, depend on the maximal distance that a large or pendulous breast might hang. We have determined that a clearance of 30 cm is sufficient for the majority of patients. It should be noted that the top of the treatment table c’n most linear accelerators cannot be elevated sufficiently lo cover the entire breast. Thus, modification of the existing accelerator treatment table may not allow the patient to be treated in this position without an elevated platform. A number of prototype platforms have been used for this study to date. In general, they involve a flat or curved surface and an adjustable circular, ovoid or slit aperture for the breast and chest wall. The initial prototype platform limited our ability to image the chest wall at the base of the breast and verify the treatment position with plain film radiographs. These problems with vertical positioning have been overcome with the development of a second prototype whose aperture consists of a simple slit that can be opened or closed to accommodate the patient’s breast size, and allows the treated breast to be comfortably positioned, palpated, radiographed, and tattooed. It should be noted that stairs are required to assist the patient in climbing onto the platform since the platform substantially elevates the treatment surface. The width of the treatment platform is determined by the width of the accelerator treatment table. In this study, to obtain an isocenter at 100 cm, the block tray accessory of the accelerator head had to be removed for treatment on our linear accelerator.’ The cranial-caudal dimensions of the breast require that the aperture and supportive elements of the platform allow for a variable field size of 1530 cm. Verification of treatment requires that portal films be taken and compared with plain films taken at the time of simulation (Fig. 2). The ribs are the most reliable radiographic landmark and provide the radiation oncologist with knowledge of the amount of chest wall, lung, and heart that fall within the treatment portals. Limitations of the prone position treatment are patient related. Large breasted women are often obese and have difficulty climbing on to the platform and lying prone as do older women. Obese individuals may also have excess nonmammary soft tissue that hangs in the treatment portal when the aperture is not properly optimized and at times requiring additional immobilization with aquaplast* or alpha-cradle’ material.
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’ Varian Clinac 6OOC, Palo Alto, CA. * Aqua-plast Corp., Wyckoff, NJ.
Fig. 2. Lateral simulation radiograph of a patient in the prone breast treatment position. The posterior field edge includes chestwall and the remainder of the breast hangs dependently through a slit aperture in the treatment platform.
RESULTS Representative isodose distributions are presented for a patient simulated in the supine and prone positions (Fig. 3). These isodose distributions are calculated for the transverse contours of the breast through the isocenter. The uniformity of the isodose distribution has been optimized in the transverse plane for both techniques through the use of field wedges. In the case of the supine treatment, the field wedges consist of mixture of 15” and 30” wedges. A combination of 15” and 30” wedges would be exchanged during the treatment course. The prone treatment requires only the use of half-field wedges which remain throughout the course of treatment. The supine isodose distribution, normalized to the chest wall interface, is characterized by a high-dose region at the apex of the breast (104% isodose) and at the periphery of the breast (116% isodose). Treatment in the prone position results in high dose regions at the apex (104%) and base (103%) that are considerable less than those of the supine position. In addition, the dose gradient across the breast is substantially reduced. We have found in general that the high dose region at the base of the breast ranges from 116- 118% for large breasted women treated in the supine position to 102- 103% for the same women treated in the prone position. Normalization of the isodose distribution is generally performed at the chest wall interface. If corrections are actually made for the volume of lung appearing in the treatment portal ofthe supine technique, the percent isodose of the high-dose regions is increased. In Figure 3 an example of corrected and uncorrected
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Fig. 3. Isodose distributions for breast treatments carried out in the prone and supine positions with transverse contours taken at the center of the treatment field. The prone position isodose
distribution (top), supine position isodose distribution (bottom) are presented with a supine position isodose distribution (right) corrected for lung transverse by the treatment field.
isodose distributions in the supine position are presented. Correction for lung within the treatment portal with normalization at the same point results in a 10% increase in the peripheral high-dose region. For breasts treated in the prone position, the selection of a reference point for normalization becomes critical in determining the magnitude of the high-dose regions. In the case of the isodose distributions presented in Figure 3, the breast-chest wall interface was selected for normalization based upon radiographic verification of the breast-chest wall interface.
Can radiation physics
DISCUSSION Although the present methods used to deliver radiation therapy to the breast result in excellent local control and cosmesis in a majority of patients, further optimization of breast radiotherapy may be possible by improving dose uniformity and reducing the dose received by normal tissues. The technique of prone position breast irradiation offers a simple and effective alternative to irradiation of the breast in the supine position when the supine position treatment is likely to result in substantial isodose nonuniformities or significant doses to the lung or heart. While the size of the breast, location of the primary tumor, and the volume of tissue removed at the time of surgery play an important role in predicting cosmetic outcome (7, 18,26) patients with large, pendulous breasts or large separations, are less likely to achieve an excellent cosmetic outcome and are more likely to suffer the side effects of dose inhomogeneities. Thus, patients with large breasts are among the group of patients most likely to gain from efforts to improve the dose distribution within the breast.
qfthe breast be improved?
There are a number of techniques that can be used to shape the distribution of dose within the breast. Slessinger et al. (24) investigated the use of a Lucite beam spoiler or layer bolus to achieve the dose buildup characteristics of 6-MV tangential photon beams for patients with large breasts treated with 18-MV photons. Using a Lucite beam spoiler suspended 13.5 cm proximal to the isocenter, a surface dose with 18-MV photons was achieved which. was within 8% of that obtained with 6-MV photons. At a depth of 3.5 mm, however, the dose with 18-MV photons was 16% lower than that obtained with 6-MV photons. At greater depths, the dose with 18-MV photons differed, on average, 10% with the dose obtained using 6MV photons. In a separate experiment, these authors found that the use of 5 mm super flab layer bolus with 18-MV photons increased the surface dose by 23% compared with 6-MV photons, however, from depths of 3.512.5 mm, the dose was within 7% of that obtained with 6-MV photons. Muller-Runkel et al. (17) investigated the use of 18-MV photons or mixed beams of 6- and 18MV photons to improve the dose homogeneity within the breast. Although the homogeneity was improved with this method, treatment breaks were required in a number of patients. Wedges are the most common beam modifier used to improve dose uniformity. The improvement in the isodose distribution, however, can only be analyzed in the plane from which a contour has been taken and contours are generally limited to the isocenter in the transverse plane. This practice neglects the assessment of dose inhomogeneities in other planes. It also accounts for the limitation of wedges that stems from the need to have the beam modified in additional planes to compensate for surface
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slope and other tissue irregularities. Wedges are often used only for a portion of the treatment and, unless used in a dynamic fashion, may lead to additional uncertainties in the estimated isodose distribution. From our limited experience with the prone position technique, and through the comparison of isodose distributions determined from the contours of large breasted women simulated in both the supine and prone positions, an improvement in dose uniformity and a reduction in the dose to normal tissues has been achieved (Fig. 3). The gradient of dose at the base of the breast is reduced in the prone position. The dose gradient from the apex of the breast to its base at the chest wall interface is also reduced in the prone position. The dose gradients calculated from contours of breasts in the supine position are actually underestimated since corrections for lung, normally present in the radiation portal at the base of the breast, are not included in the isodose calculations. When a patient is treated in the prone positia’n, the volume of lung included in the radiation portal is either nonexistent or too small to require a correction. This claim requires verification using computed tomography. If the lung volume in the prone position is small or nonexistent, the isodose gradients, described for the breast treated in the prone position, are a realistic representation of dose deposited in an approximate cylinder ‘of tissue. Ordinarily, the dose distribution for any patient treated in the supine position is depicted using a contour of the patient’s axial anatomy at the center of the breast. This practice ignores the patient’s axial contours at the most extreme cranial and caudal levels, as well as prone the sagittal dose distribution which, through the center, would include the extreme cranial and caudal aspects of the breast. When the breast is treated in the prone position, as the breast hangs dependently to form an imperfect cylinder, the axial contour and dose distribution, like those presented in this study, are more representative elf the dose distribution in the sagittal plane. This is especially true when pendulous breasts with large inframammary folds are encountered. The same approximate cylindrical symmetry for the isodose distribution cannoi. be achieved for breasts treated in the supine position since the breast can take many forms in the sagittal plane. The marked difference between transverse and sagittal dose distributions was previously described by Svensson et al. (25).
What are the implications
qf improved dose uniformity
Good to excellent cosmetic results can be achieved in SO-90% of patients treated with meticulous surgery and radiotherapy techniques. Even with careful radiotherapy, which limits whole-breast and boost doses to those levels known to result in excellent cosmesis and local control, the risk of breast fibrosis, soft tissue necrosis and rib fractures remain measurable (19, 26). With the use of concurrent chemotherapy, there is an increased incidence of acute skin toxicity (7, 20). The risks of side effects are
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further amplified in women with large or pendulous breasts who are less likely to achieve excellent cosmetic results because of nonuniformities in the dose distribution. Pierce et al. ( 19) evaluated the long-term complications of radiation therapy in patients with early stage breast cancer treated with breast conserving surgery. In their analysis of 1624 patients followed for a median of 79 months, the incidence of rib fractures differed significantly between 4 and 6- or 8-MV accelerators (0.4 vs. 2.2%) and whole breast dose of 45 Gy or less and 45-50 Gy (1.4% vs. 5.7%) treated using 4-MV photons. They noted an 0.18% rate of soft tissue necrosis requiring surgical correction. Although these authors did not mention the rate incidence of poor cosmetic outcome due to fibrosis, Van the influence of total Limbergen et al. (26) investigated dose, fractionation and surgery on cosmetic outcome in 142 patients analyzed for cosmetic outcome, asymmetry and retraction due to fibrosis. They discovered that when the dose to the breast exceeded 75 Gy, the incidence of poor cosmetic outcome exceeded 30%. They quantified fibrosis and determined that a dose response occurred for total doses between 40 and 86 Gy when the fraction sizes exceeded 2 Gy. For each additional 1 Gy above 50 Gy, a linear displacement in the nipple and loss of breast contour could be measured. Their findings also revealed that segmentectomy compared to tumorectomy, en bloc compared to separate incisions and nodal irradiation compared to the use of tangents only, were associated with a significantly high risk of poor cosmetic outcome. Treatment complications such as fibrosis, rib fractures, and soft tissue necrosis result from areas of dose inhomogeneity that result in high-dose regions or gradients. In the acute setting, dose inhomogeneities lead to the skin reactions that are noted in the periphery of the breast when the patient, treated in the supine position, approaches the completion of whole breast radiotherapy.
What are the implications volumes?
qf reduced normal tissue
There are a number of reported experiences that assess the risks associated with the irradiation of normal tissue structures as a part of breast conserving surgery and adjuvant radiation therapy. There is also a body of evidence that implicates radiation therapy to the breast as less than innocuous. This makes optimization of radiotherapy techniques and the reduction in dose to normal tissue volumes even more important (22). Roberson et al. (2 1) calculated dose-volume curves using anatomic data derived from CT scans of the chest with patients in the supine treatment position. Their curves show that 22% of the ipsilateral lung receives at least 85% of the total dose using standard tangents (medial entrance 3 cm beyond midline and lateral entrance point 1 cm below palpable breast marked clinically) and approximately 38% of the ipsilateral lung receives at least 85% of the total dose when using deep tangents (fields
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moved parallel to standard tangents until the entire sternum is in the field). The risk of symptomatic pneumonitis, pericarditis and second primary tumors as a result of radiation therapy have been determined by a number of groups. According to Lingos et al. (19) when tangential fields are used alone, pneumonitis occurs in 1.0% of patients. They also described pneumonitis as being correlated with the use of chemotherapy and occurring independent of the volume of lung treated, although their range of volumes was limited and not directly measured. Pierce et al. (19) also showed that pericarditis occurred in 0.4% (3/831) of women treated with left breast irradiation and that chest wall sarcomas developed in 0.18% (3/ 1624) of women treated with breast radiotherapy. Boice et al. ( 1) concluded that the risk of radiationinduced contralateral breast cancer is small and not a consideration for selecting treatment. Curtis et al. (5) stated that the relative risk of leukemia following breast irradiation was 2.4% and depended on the volume of bone marrow irradiated. Techniques which further reduce the volume of chest wall irradiated as a part of adjuvant breast radiotherapy may have an impact on these statistics (6). The prone position method reduces the volume of lung, heart, and chest wall in the radiation therapy portal. Furthermore, the prone position breast treatment reduces the dose to the contralateral breast by several mechanisms as described by Frass et al. (10): (a) When the breast hangs in a dependent fashion away from the chest wall, the volume of chest wall that requires treatment with tangential fields is reduced and subsequently, a substantial amount of internal scatter; (b) The prone position treatment does not require the use of blocking material which can result in a nonalignment of beam edges and increase the dose to the opposite breast; (c) The treatment platform can be designed to include additional shielding materials and reduce the perpendicular distance of the contralateral breast from the field edge; (d) Wedges are either not required or their angle is reduced with the prone technique, therefore, fewer monitor units are necessary to overcome beam attenuation by the wedges. In spite of the fact that considerable work has been performed to determine ways to minimize the dose to normal structures and to determine the symptomatic acute and long-term side effects of treatment, the asymptomatic functional deficits, which may manifest themselves clinically in other forms of morbidity, await evaluation using functional imaging techniques such as SPECT to measure flow in irradiated lung ( 14).
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What are the negative ramifications of prone position breast irradiation? From a technological standpoint, it is apparent that nodal irradiation is not practical with this technique. This does not diminish the value of the technique since there are many large breasted women with node-negative invasive breast cancer or ductal carcinoma in situ who could benefit from the use of the prone technique. From an oncologic point of view, a smaller amount of chest wall is irradiated when compared to the supine position. The location of breast tissue with respect to the chest wall, with the patient in the supine position, has been verified by magnetic resonance imaging (MRI) studies (15, 16) performed in the prone position. Magnetic resonance imaging has been used to improve breast surgery treatment planning ( 15) and may help to select patients for the prone position treatment and define a subset of patients in whom irradiation of the entire chest wall using the horizontally opposed tangential fields is required. Fowble et al. (9) show that there was no difference in the patterns of failure, or 5-year actuarial, relapse-free and NED survival in 886 patients with Stage I and II breast cancer analyzed according to the site of the primary disease in the breast. Although patients were treated in the supine position for that series, the experience of the Curie Institute, using breast conserving surgery and adjuvant radiation therapy performed in the decubitus position, supports the use of the prone position as an alternative technique for breast irradiation. Calle et al. (2, 3) reported the IO-year results from the Curie Institute as 90% (290/324) NED survival at 5 years and 8 1% ( 140/ 173) NED survival at 10 years. Mammary and axillary recurrences were reported to be 8% at 5 years and 10% at 10 years with the majority of recurrences occurring at the tumorectomy site. Prone position irradiation of the breast is a feasible alternative to supine position treatment for patients with large medial to lateral separations or other morphological aspects that result in nonuniform isodose distributions when treated in the supine position. Improving the dose distribution throughout the breast may prove beneficial in increasing the tolerability of concomitant chemotherapy by reducing the risk of acute and long-term side effects. The reduction in the volume of normal tissue irradiated with this technique has the potential to benefit women with preexisting pulmonary or cardiac diseases undergoing breast conserving therapy. Large breasted women appear to benefit most from this treatment, although women of all sizes may benefit once additional verification of the technique and a comparison of normal tissue volumes is carried out using computed tomography.
REFERENCES 1. Boice, J. D.; Harvey, E. B.; Blettner, M. Cancer in the breast after radiotherapy for breast cancer. N. Engl. J. Med. 326: 781-785; 1992. 2. Calle, R. Primary breast cancer: European radiotherapy trials. Clin. Trials Cancer Med. 8: 123-l 36; 1985.
3. Calle, R.; Pilleron, J. P.; Schlienger, P.; Vilcoq, J. R. Conservative management of operable breast cancer. Ten years experience at the foundation curie. Cancer 42:2045-2053; 1978. 4. Cross, M. A.; Elson, H. R.; Aron, B. S. Breast conservation
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radiation therapy technique for women with large breasts. Int. J. Radiat. Oncol. Biol. Phys. 17: 199-203; 1989. Curtis, R. E.; Boice, J. D.; Stovall, M. Risk of leukemia after chemotherapy and radiation treatment for breast cancer. N. Engl. J. Med. 326: 174.5-175 1; 1992. DeLaney, T. F.; Pierce, Id. J. Cancer in the contralateral breast after radiotherapy for breast cancer. N. Eng. J. Med. 327:430; 1992. de la Rochfordiere, A.; Abner, A. L.; Silver, B.; Vicini, F.; Recht, A.; Harris, J. R. Are cosmetic results following conservative surgery and radiation therapy for early breast cancer dependent on technique? Int. J. Radiat. Oncol. Biol. Phys. 23:925-93 1; 1992. Fleck, R.; McNeese, M. D.; Ellerbroek, N. A.; Hunter, T. A.; Holmes, F. A. Consequences of breast irradiation in patients with preexisting collagen vascular diseases. Int. J. Radiat. Oncol. Biol. Phys. 17829-833; 1989. Fowble, B.; Solin, L. J.; Schultz, D. J.; Weiss, M. C. Breast recurrence and survival related to primary tumor location in patients undergoing conservative surgery and radiation for early stage breast cancer. Int. J. Radiat. Oncol. Biol. Phys. 23:933-939; 1992. Frass, B. A.; Roberson, F’. L.; Lichter, A. S. Dose to the contralateral breast due to primary breast irradiation. Int. J. Radiat. Oncol. Biol. Phys. 11:485-497; 1985. Gray, J. R.; McCormick, 13.;Cox, L.; Yahalom, J. Primary breast irradiation in large-breasted or heavy women: Analysis of cosmetic outcome. Int. J. Radiat. Oncol. Biol. Phys. 21: 347-354; 1991. Hunt, M. A.; Kutcher, G. J.; Martel, M. K. Matchline dosimetry of a three field technique for breast treatment using cobalt or 6-MV X rays. Int. J. Radiat. Oncol. Biol. Phys. 13:1099-l 106; 1987. Lingos, T. I.; Recht, A.; Vicini, F.; Abner, A.; Silver, B.; Harris, J. R. Radiation pneumonitis in breast cancer patients treated with conservative surgery and radiation therapy. Int. J. Radiat. Oncol. Biol. Phys. 21:355-360; 1991. Marks, L; Sontag, M; Spencer, D.; Ray, S; Antoine, P; Sherouse, G; Bentel, G; Coleman, R. E.; Jasczak, R.; Tapson, V.; Prosnitz, L. Three dimensional SPECT lung perfusion scans in designing radiation beams and in predicting and assessing the physiological consequences of thoracic irradiation (Abstract 191). Int. J. Radiat. Oncol. Biol. Phys. 24: 238; 1992. Merchant, T. E.; Obertop, H.; de Graaf, P. W. Advantages of magnetic resonance imaging in breast surgery treatment planning. Breast Cancer Res. Treat. 25:257-264; 1993. Merchant, T. E.; Thelissen, G. R. P.; Kievit, H. C. E.; Oosterwaal, L. J. M. P.; Bakker, C. J. G.; de Graaf, P. W. Breast disease evaluation with fat-suppressed magnetic resonance imaging. Magn. Reson. Imag. 10:335-340; 1992.
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17. Muller-Runkel, R.; Kalokhe, U. P.; Schreiber, G. Radiation therapy of unusually large breasts: Using higer energy photons with or without bolus for all or part of the treatment course. Poster 1070, ASTRO 1991. 18. Olivotto, I. A.; Rose, M. A.; Osteen, R. T.; Love, S.; Cady, B.; Silver, B.; Recht, A.; Harris, J. R. Late cosmetic outcome after conservative surgery and radiotherapy: Analysis of causes of cosmetic failure. Int. J. Radiat. Oncol. Biol. Phys. 171747-753; 1989. 19. Pierce, S. M.; Recht, A.; Lingos, T. I.; Abner, A.; Vicini, F.; Silver, B.; Herzog, A.; Harris, J. R. Long-term radiation complications following conservative surgery (CS) and radition therapy in patients with early stage breast cancer. Int. J. Radiat. Oncol. Biol. Phys. 23:915-923; 1992. 20. Ray, G. R.; Fish, V. J.; Marmor, J. B.; Rogoway, W.; KushIan, P.; Arnold, C.; Lee, R. H.; Marzoni, F. Impact of adjuvant chemotherapy on cosmesis and complications in Stages I and II carcinoma of the breast treated by biopsy and radiation therapy. Int. J. Radiat. Oncol. Biol. Phys. 10: 837-841; 1984. 21. Roberson, P. L.; Lichter, A. S.; Bodner, A.; Fredrickson, H. A.; Padikal, T. N.; Kelly, B. A.; van de Geijn, J. Dose to lung in primary irradiation. Int. J. Radiat. Oncol. Biol. Phys. 9:97-102; 1982. 22. Rotstein, S; Lax, 1.; Svane, G. Influence of radiation therapy on the lung tissue in breast cancer patients: CT-assessed density changes and associated symptoms. Int. J. Radiat. Oncol. Biol. Phys. 18:173-180; 1990. 23. Siddon, R. L.; Buck, B. A.; Harris, J. R.; Svensson, G. K. Three-field technique for breast irradiation using tangential corner blocks. Int. J. Radiat. Oncol. Biol. Phys. 9:583-588; 1983. 24. Slessinger, E. D.; Devineni, V. R.; Lewis, P. Early breast cancer: Duplication of 6-MV dose buildup with 18-MV X rays in patients with large separations (Abstract 1095). Int. J. Radiat. Oncol. Biol. Phys. 24:295; 1992. 25. Svensson, G. K.; Siddon, R. L.; Chin, L. M.; Harris, J. R. Breast treatment techniques at the Joint Center for Radiation Therapy. In: Harris, J. R., Hellman, S., Silen, W., eds. Conservative management of breast cancer. 239-257. 26. Van Limbergen, E.; Rijnders, A.; van der Schueren, E.; Lerut, T.; Christiaens, R. Cosmetic evaluation of breast conserving treatment for mammary cancer. 2. A quantitative analysis of the influence of radiation dose, fractionation schedules and surgical treatment techniques on cosmetic results. Radiother. Oncol. 16:253-267; 1989. 27. Vilcoq, J. R.; Calle, R.; Schlienger, P. Irradiation techniques for conservative treatment of localized breast cancer. In: Harris, J. R., Hellman, S., Silen, W., eds. Conservative management of breast cancer. 2 13-224.