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Dosimetric considerations of water-based bolus for irradiation of extremities
Medical Dosimetry, Vol. 23, No. 4, pp. 292–295, 1998 Copyright © 1998 American Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947/98/$–see front matter
PII S0958-3947(98)00033-8
● Original Contribution
DOSIMETRIC CONSIDERATIONS OF WATER-BASED BOLUS FOR IRRADIATION OF EXTREMITIES CHENG B. SAW, PH.D., B-CHEN WEN, M.D., K. ANDERSON, C.M.D., E. PENNINGTON, M.S., and DAVID H. HUSSEY, M.D. Division of Radiation Oncology, University of Iowa Hospitals & Clinics, Iowa City, IA 52242 Abstract—The dosimetry of high-energy photon beams in the treatment of superficial lesions occurring in extremities was examined. Large parallel-opposed fields with different photon beam energies were used. The extremity was immersed in water contained in a commercially available plastic wastebasket. The water bolus serves to even out the surface irregularities of the extremities and to remove the skin sparing effect. A polystyrene block was placed at the floor of the wastebasket to ensure that the extremity was encompassed in the radiation fields. The photon beam energies considered were 4 MV, 6 MV, 10 MV, and 24 MV. The results show that the dose distributions are more homogeneous with higher photon beam energies. The isodose lines are more constricted at mid-plane for low energy photon beams. Higher energy photon beams, 10 MV and up would be preferable for the treatment of superficial lesions of the extremities immersed in water bolus contained in a typical wastebasket size. © 1998 American Association of Medical Dosimetrists. Key Words: Photon beam, External beam, Dosimetry, Bolus.
INTRODUCTION
ity to be treated is immersed into the water as shown in Fig. 1. The setup illustrated in the figure is for the treatment of a lower extremity tumor in which the patient sits on a chair positioned on top of the treatment couch. Care should be exercised to minimize the possibility of the patient or chair falling from the treatment couch. The bucket that holds the water is a plastic wastebasket that can be purchased from any department store. The wastebasket is made of 3 mm thick plastic with an overall dimension of 24 cm 3 38 cm 3 43 cm. Due to the bulging effect when full of water, the wastebasket is reinforced with a 6 mm thick masonite sheet on either side of the wastebasket. Perforated polystyrene or acrylic blocks have been added to the base of the wastebasket so that the lower extent of the extremity is encompassed in the radiation field. The collimator of the linear accelerator can be opened to cover the size of the wastebasket and, if necessary, can be reduced to limit exposure to normal tissue. Radiation is delivered bilaterally through parallel-opposed fields. The dosimetry for this technique using parallelopposing fields was studied with different photon beam energies. The inter-field thickness includes both the thickness of the wastebasket and the thickness of the masonite. An isocentric technique was employed. A field size of 30 cm 3 30 cm was also used. The photon beam energies studied were 4 MV, 6 MV, 10 MV, and 24 MV.
Superficial skin tumors occurring in the extremities are generally treated with appositional electron or low-energy x-ray fields. The treatment of a large area requires the abutment of multiple fields because the field size for electron beams and low-energy x-ray beams is limited and this can result in hot and cold spots at junctions of these fields. An alternative technique would be to use megavoltage photon beams and a parallel-opposed field arrangement that deliver a homogenous dose throughout the extremity. The megavoltage photon beam may have too much skin sparing effect if the lesion is located superficially. In this case, bolus can be used to eliminate the skin sparing effect. Liquid bolus, like water, provides automated conformation to the curvature of the extremities that effectively eliminates the skin sparing effect. The use of water-based bolus with Cobalt-60 photon beams in the treatment of Kaposi’s sarcoma has been published.1 This study examined the dosimetric aspects of the treatment using water-based bolus and higher photon beam energies from 4 MV to 24 MV. MATERIALS AND METHODS The treatment setup consists of a bucket of water placed at the isocenter of linear accelerator. The extremReprint requests to: Cheng B. Saw, Ph.D., Division of Radiation Oncology, University of Iowa Hospitals & Clinics, 200 Hawkins Dr W189Z-GH, Iowa City, IA 52242. 292
Dosimetric considerations of water-based bolus for irradiation of extremities ● C. B. SAW et al.
293
Fig. 1. Clinical setup for the treatment of lower extremity with water bolus.
RESULTS The dose distributions of the large parallel-opposed fields for the four photon beam energies are shown in Fig. 2. The dose distributions were normalized to the isocenter. The maximum doses are 17% more than the isocenter dose for 4 MV photon beam, 10% more than the isocenter for 6 MV photon beam, and 7% more than the isocenter dose for both 10 MV and 24 MV photon beams. As such, the 10 MV or 24 MV photon beam produces the most homogeneous dose distribution. The lower energies photon beam also shows a distinct hourglass effect phenomenon with constriction of isodose lines in the middle of the treatment volume. The constriction is apparent at isodose lines greater than 95% isodose line for the 4 MV photon beam and at isodose lines greater that 96% for the 6 MV photon beam. The constrictions are not present at the 98% for 10 MV and 100% for 24 MV photon beams. Therefore, the best dose uniformity is achieved with higher photon beam energies. This study suggests that photon beam energies of 10 MV or higher is preferable for the treatment of superficial lesions of extremities using this water bolus size. Lower photon beam energies exhibit constriction of isodose lines. The isodose distribution also shows that the
dose varies slowly from the center to the edge of the phantom symmetrically. This suggest that uniform dose distribution can still be achieved using lower photon energies provided that the size of the extremity is small and positioned centrally within the water bolus. DISCUSSION Although this dosimetric study can be used for all superficial lesions of the extremities, the technique is often used in the treatment of Kaposi’s sarcoma. Kaposi’s sarcoma is an epidemic disease often associated with adult immunodeficient syndrome. It tends to arise from multiple foci in the skin with the clinical presentation of macules, papules, plaques, and ultimately fungating mass with ulceration and bleeding. If the lesion involves part of the leg, it tends to obstruct the flow of the lymphatic system causing edema without apparent sign of visible lesion or lymph node enlargement as the lesion progresses. Kaposi’s sarcoma is the first manifestation of acquired immune disease syndrome (AIDS) in 30%– 40% of the patients. Due to its multicentric and infiltrating/aggressive nature, Kaposi’s sarcoma often is presented with widely disseminated disease with extensive involvement of extremities and/or trunk. Radiation therapy remains the
294
Medical Dosimetry
Volume 23, Number 4, 1998
Fig. 2. Isodose distributions of parallel-opposed fields using: (a) 4 MV, (b) 6 MV, (c) 10 MV, and (d) 24 MV photon beams. The dose inhomogeneity is about 17% for 4 MV, 10% for 6 MV, and 7% for 10 and 24 MV photon beams.
Dosimetric considerations of water-based bolus for irradiation of extremities ● C. B. SAW et al.
treatment of choice for pain relief or to control bleeding in many of these patients. The response rate to radiation therapy is about 80%–90%.2–5. Irradiation of a single solitary Kaposi’s sarcoma generally includes the lesion and 2.0 to 4.0 cm of surrounding normal tissue. Electron beam with bolus or superficial x-ray beam are the preferred modes of radiation therapy since the disease is usually limited to dermis. However, for patients with extremity disease involving deeper tissues, electron beam treatment of the entire extremity is not an optimal solution. In this situation, parallel-opposed high-energy photon beam fields and bolus may be a better alternative because the dose distribution is more homogenous. In this paper we describe a simple technique of delivering a homogeneous dose distribution to the extremities with the appropriate photon beam energy. Excellent palliation can be achieved with doses of approximately 20 –30 Gy6 – 8 since Kaposi’s sarcoma is a radiation sensitive tumor. The use of a water-based bolus has several advantages and disadvantages. Fabrication of the water-based bolus is simple since the wastebasket can be purchased from most department stores. The thickness of the wastebasket is minimal so that attenuation correction is not necessary. The bolus is liquid and hence easily conforms to the shape of the extremities. However, the use of water-based bolus results in the loss of the skin sparing effects of high-energy photon beams although this effect is not needed. There is also the possibility of water spillage which can be inconvenient. Additional precaution may be taken by placing the patient extremity in a plastic bag prior to inserting into the water bath as shown in Fig. 1. This procedure would minimize contamination of the water with secretion and also keeps the patient extremity dry which is important if the extremity is the leg since it is used to dismount from the treatment couch. To summarize, this work shows that a water-based
295
bolus for the treatment of extremities can be easily fabricated with accessible material in any radiation facility. The water is contained within a typical wastebasket that can be purchased from any department store. Some form of material such as superflab, or polystyrene block may be needed to raise the foot above the floor of the wastebasket. This treatment technique avoids dose inhomogeneity, i.e. cold and hot spots that occur with abutting electron beam or superficial x-ray fields commonly used to treat superficial skin tumors. This dosimetric study shows that photon beams with 10 MV or higher would produce a more homogenous dose distribution than can be achieved with lower energy megavoltage beams. REFERENCES 1. Weshler, Z.; Loewinger, E.; Loewenthal, E.; Levinson, R.; Fuks, Z. Megavoltage radiotherapy using water bolus in the treatment of Kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 12:2029 –2032; 1986. 2. Harrison, M.; Harrington, K.J.; Tomlinson, D.R.; Stewart, J.S.W. Response and cosmetic outcome of two fractionation regimens for AIDS-related Kaposi’s sarcoma. Radiother. Oncol. 46:23–28; 1998. 3. Kirova, Y.M.; Belembaogo, E.; Frikha, H.; Haddad, E.; Calitchi, E.; Levy, E.; Piedbois, P.; Le Bourgeois, J.P. Radiotherapy in the management of epidemic Kaposi’s sarcoma: a retrospective study of 643 cases. Radiother. Oncol. 46:19 –22; 1998. 4. Cooper, J.S.; Fried, P.R.; Laubenstein, L.J. Initial observations of the effect of radiotherapy on epidemic kaposi’s sarcoma. JAMA 252:934 –935; 1984. 5. Nobler, M.P.; Leddy, M.E.; Huh, S.H. The impact of palliative irradiation on the management of patients with acquired immune deficiency syndrome. J. Clin. Oncol. 5:107–112; 1987. 6. Chak, L.Y.; Gill, P.S.; Levine, A.M.; Meyer, P.R.; Anselino, J.A.; Petrovich, Z. Radiation therapy for acquired immunodeficiency syndrome related kaposi’s sarcoma. J. Clin. Oncol. 6:863– 867; 1998. 7. Stelzer, K.J.; Griffin, T.W. A randomized prospective trial of radiation therapy for aids-associated kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 27:1057–1061; 1993. 8. Cooper, J.S.; Steinfeld, A.D.; Lerch, I. Intentions and outcomes in the radiotherapeutic management of epidemic kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 20:419 – 422; 1991.
PII S0958-3947(98)00033-8
● Original Contribution
DOSIMETRIC CONSIDERATIONS OF WATER-BASED BOLUS FOR IRRADIATION OF EXTREMITIES CHENG B. SAW, PH.D., B-CHEN WEN, M.D., K. ANDERSON, C.M.D., E. PENNINGTON, M.S., and DAVID H. HUSSEY, M.D. Division of Radiation Oncology, University of Iowa Hospitals & Clinics, Iowa City, IA 52242 Abstract—The dosimetry of high-energy photon beams in the treatment of superficial lesions occurring in extremities was examined. Large parallel-opposed fields with different photon beam energies were used. The extremity was immersed in water contained in a commercially available plastic wastebasket. The water bolus serves to even out the surface irregularities of the extremities and to remove the skin sparing effect. A polystyrene block was placed at the floor of the wastebasket to ensure that the extremity was encompassed in the radiation fields. The photon beam energies considered were 4 MV, 6 MV, 10 MV, and 24 MV. The results show that the dose distributions are more homogeneous with higher photon beam energies. The isodose lines are more constricted at mid-plane for low energy photon beams. Higher energy photon beams, 10 MV and up would be preferable for the treatment of superficial lesions of the extremities immersed in water bolus contained in a typical wastebasket size. © 1998 American Association of Medical Dosimetrists. Key Words: Photon beam, External beam, Dosimetry, Bolus.
INTRODUCTION
ity to be treated is immersed into the water as shown in Fig. 1. The setup illustrated in the figure is for the treatment of a lower extremity tumor in which the patient sits on a chair positioned on top of the treatment couch. Care should be exercised to minimize the possibility of the patient or chair falling from the treatment couch. The bucket that holds the water is a plastic wastebasket that can be purchased from any department store. The wastebasket is made of 3 mm thick plastic with an overall dimension of 24 cm 3 38 cm 3 43 cm. Due to the bulging effect when full of water, the wastebasket is reinforced with a 6 mm thick masonite sheet on either side of the wastebasket. Perforated polystyrene or acrylic blocks have been added to the base of the wastebasket so that the lower extent of the extremity is encompassed in the radiation field. The collimator of the linear accelerator can be opened to cover the size of the wastebasket and, if necessary, can be reduced to limit exposure to normal tissue. Radiation is delivered bilaterally through parallel-opposed fields. The dosimetry for this technique using parallelopposing fields was studied with different photon beam energies. The inter-field thickness includes both the thickness of the wastebasket and the thickness of the masonite. An isocentric technique was employed. A field size of 30 cm 3 30 cm was also used. The photon beam energies studied were 4 MV, 6 MV, 10 MV, and 24 MV.
Superficial skin tumors occurring in the extremities are generally treated with appositional electron or low-energy x-ray fields. The treatment of a large area requires the abutment of multiple fields because the field size for electron beams and low-energy x-ray beams is limited and this can result in hot and cold spots at junctions of these fields. An alternative technique would be to use megavoltage photon beams and a parallel-opposed field arrangement that deliver a homogenous dose throughout the extremity. The megavoltage photon beam may have too much skin sparing effect if the lesion is located superficially. In this case, bolus can be used to eliminate the skin sparing effect. Liquid bolus, like water, provides automated conformation to the curvature of the extremities that effectively eliminates the skin sparing effect. The use of water-based bolus with Cobalt-60 photon beams in the treatment of Kaposi’s sarcoma has been published.1 This study examined the dosimetric aspects of the treatment using water-based bolus and higher photon beam energies from 4 MV to 24 MV. MATERIALS AND METHODS The treatment setup consists of a bucket of water placed at the isocenter of linear accelerator. The extremReprint requests to: Cheng B. Saw, Ph.D., Division of Radiation Oncology, University of Iowa Hospitals & Clinics, 200 Hawkins Dr W189Z-GH, Iowa City, IA 52242. 292
Dosimetric considerations of water-based bolus for irradiation of extremities ● C. B. SAW et al.
293
Fig. 1. Clinical setup for the treatment of lower extremity with water bolus.
RESULTS The dose distributions of the large parallel-opposed fields for the four photon beam energies are shown in Fig. 2. The dose distributions were normalized to the isocenter. The maximum doses are 17% more than the isocenter dose for 4 MV photon beam, 10% more than the isocenter for 6 MV photon beam, and 7% more than the isocenter dose for both 10 MV and 24 MV photon beams. As such, the 10 MV or 24 MV photon beam produces the most homogeneous dose distribution. The lower energies photon beam also shows a distinct hourglass effect phenomenon with constriction of isodose lines in the middle of the treatment volume. The constriction is apparent at isodose lines greater than 95% isodose line for the 4 MV photon beam and at isodose lines greater that 96% for the 6 MV photon beam. The constrictions are not present at the 98% for 10 MV and 100% for 24 MV photon beams. Therefore, the best dose uniformity is achieved with higher photon beam energies. This study suggests that photon beam energies of 10 MV or higher is preferable for the treatment of superficial lesions of extremities using this water bolus size. Lower photon beam energies exhibit constriction of isodose lines. The isodose distribution also shows that the
dose varies slowly from the center to the edge of the phantom symmetrically. This suggest that uniform dose distribution can still be achieved using lower photon energies provided that the size of the extremity is small and positioned centrally within the water bolus. DISCUSSION Although this dosimetric study can be used for all superficial lesions of the extremities, the technique is often used in the treatment of Kaposi’s sarcoma. Kaposi’s sarcoma is an epidemic disease often associated with adult immunodeficient syndrome. It tends to arise from multiple foci in the skin with the clinical presentation of macules, papules, plaques, and ultimately fungating mass with ulceration and bleeding. If the lesion involves part of the leg, it tends to obstruct the flow of the lymphatic system causing edema without apparent sign of visible lesion or lymph node enlargement as the lesion progresses. Kaposi’s sarcoma is the first manifestation of acquired immune disease syndrome (AIDS) in 30%– 40% of the patients. Due to its multicentric and infiltrating/aggressive nature, Kaposi’s sarcoma often is presented with widely disseminated disease with extensive involvement of extremities and/or trunk. Radiation therapy remains the
294
Medical Dosimetry
Volume 23, Number 4, 1998
Fig. 2. Isodose distributions of parallel-opposed fields using: (a) 4 MV, (b) 6 MV, (c) 10 MV, and (d) 24 MV photon beams. The dose inhomogeneity is about 17% for 4 MV, 10% for 6 MV, and 7% for 10 and 24 MV photon beams.
Dosimetric considerations of water-based bolus for irradiation of extremities ● C. B. SAW et al.
treatment of choice for pain relief or to control bleeding in many of these patients. The response rate to radiation therapy is about 80%–90%.2–5. Irradiation of a single solitary Kaposi’s sarcoma generally includes the lesion and 2.0 to 4.0 cm of surrounding normal tissue. Electron beam with bolus or superficial x-ray beam are the preferred modes of radiation therapy since the disease is usually limited to dermis. However, for patients with extremity disease involving deeper tissues, electron beam treatment of the entire extremity is not an optimal solution. In this situation, parallel-opposed high-energy photon beam fields and bolus may be a better alternative because the dose distribution is more homogenous. In this paper we describe a simple technique of delivering a homogeneous dose distribution to the extremities with the appropriate photon beam energy. Excellent palliation can be achieved with doses of approximately 20 –30 Gy6 – 8 since Kaposi’s sarcoma is a radiation sensitive tumor. The use of a water-based bolus has several advantages and disadvantages. Fabrication of the water-based bolus is simple since the wastebasket can be purchased from most department stores. The thickness of the wastebasket is minimal so that attenuation correction is not necessary. The bolus is liquid and hence easily conforms to the shape of the extremities. However, the use of water-based bolus results in the loss of the skin sparing effects of high-energy photon beams although this effect is not needed. There is also the possibility of water spillage which can be inconvenient. Additional precaution may be taken by placing the patient extremity in a plastic bag prior to inserting into the water bath as shown in Fig. 1. This procedure would minimize contamination of the water with secretion and also keeps the patient extremity dry which is important if the extremity is the leg since it is used to dismount from the treatment couch. To summarize, this work shows that a water-based
295
bolus for the treatment of extremities can be easily fabricated with accessible material in any radiation facility. The water is contained within a typical wastebasket that can be purchased from any department store. Some form of material such as superflab, or polystyrene block may be needed to raise the foot above the floor of the wastebasket. This treatment technique avoids dose inhomogeneity, i.e. cold and hot spots that occur with abutting electron beam or superficial x-ray fields commonly used to treat superficial skin tumors. This dosimetric study shows that photon beams with 10 MV or higher would produce a more homogenous dose distribution than can be achieved with lower energy megavoltage beams. REFERENCES 1. Weshler, Z.; Loewinger, E.; Loewenthal, E.; Levinson, R.; Fuks, Z. Megavoltage radiotherapy using water bolus in the treatment of Kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 12:2029 –2032; 1986. 2. Harrison, M.; Harrington, K.J.; Tomlinson, D.R.; Stewart, J.S.W. Response and cosmetic outcome of two fractionation regimens for AIDS-related Kaposi’s sarcoma. Radiother. Oncol. 46:23–28; 1998. 3. Kirova, Y.M.; Belembaogo, E.; Frikha, H.; Haddad, E.; Calitchi, E.; Levy, E.; Piedbois, P.; Le Bourgeois, J.P. Radiotherapy in the management of epidemic Kaposi’s sarcoma: a retrospective study of 643 cases. Radiother. Oncol. 46:19 –22; 1998. 4. Cooper, J.S.; Fried, P.R.; Laubenstein, L.J. Initial observations of the effect of radiotherapy on epidemic kaposi’s sarcoma. JAMA 252:934 –935; 1984. 5. Nobler, M.P.; Leddy, M.E.; Huh, S.H. The impact of palliative irradiation on the management of patients with acquired immune deficiency syndrome. J. Clin. Oncol. 5:107–112; 1987. 6. Chak, L.Y.; Gill, P.S.; Levine, A.M.; Meyer, P.R.; Anselino, J.A.; Petrovich, Z. Radiation therapy for acquired immunodeficiency syndrome related kaposi’s sarcoma. J. Clin. Oncol. 6:863– 867; 1998. 7. Stelzer, K.J.; Griffin, T.W. A randomized prospective trial of radiation therapy for aids-associated kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 27:1057–1061; 1993. 8. Cooper, J.S.; Steinfeld, A.D.; Lerch, I. Intentions and outcomes in the radiotherapeutic management of epidemic kaposi’s sarcoma. Int. J. Radiat. Oncol. Biol. Phys. 20:419 – 422; 1991.