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Evaluating the dose to the contralateral breast when using a dynamic wedge versus a regular wedge
Copyright
Perg~oN
Medical 0 I995
Dosimetry. American
Vol. 20, No. 4, pp. 287-293, 1995 Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947195 $9.50 + .oo
0958-3947(95)02011-X
EVALUATING WHEN USING CHRISTOPHER
THE DOSE TO THE CONT~LATE~L BRIEAST A DYNAMIC WEDGE VERSUS A REGULAR WEDGE
D. WEIDES,
EDWARD
C. ?vkx, WENDY C. CHANG, and CAROL A. SHOSTAK
DAVID
0. FINDLEY,
Stanford University School of Medicine, Department of Radiation Oncology. Stanford, California 94305-5 105 Abstract--The incidence of secondary cancersin the contralateral breast after primary breast irradiation is several times higher than the incidence of first time breast cancer. Studies have shown that the scatter radiation to the contralateral breast may pIay a huge part in the induction of secondary breast cancers. Factors that may contribute to the contralateral breast dosemay include the useof blocks, the orientation of the field, and wedges.Reports have shown that the use of regular wedges,particularly for the medial tangential field, gives a si~ifican~y higher doseto the contralateral breast compared to an openfield. This paper comparesthe peripheral doseoutsidethe field using a regular wedge,a dynamic wedge,and au open field technique. The data colbxted consistedof measurementstaken with patients, solid water and a Rando phantom using a Varian 2300CDlinear accelerator. ion chambers,thermoluminescentdosimeters(TLD) , diodes,and Almswere the primary meansfor collecting the data. The measurementsshowthat the peripheral doseoutside the field using a dynamic wedgeis close to that of open fields, and signiiicantly lower than that of regular wedges.This isolation indicatesthat when usinga medial wedge,a dynamic wedgeshould be used. Key Words:Contralateral,Breast, Dynamic wedge, Dose.
dealt with removing the wedge from the medial tangent field. Other studies also show that the majority of the contralateral breast dose is produced by the medial tangent beam, whereas, the dose from the lateral tangent beam has to transverse through several centimeters of tissue before it reaches the contralateral breast.7.X.‘,‘0 The isodose distribution, with only the lateral wedge, does give an acceptable treatment plan most of the time, but there are still times when a medial wedge would improve the isodose dis~bution throughout the treatment volume. Advances in technology have provided the necessary means to accompIish the goal of reducing the radiation dose to the contralateral breast. A device known as a dynamic wedge should prove to be useful in decreasing the dose and yet maintaining a medial wedge. The dynamic wedge uses the primary collimator jaws to create the wedge effect as it moves across the field in a computer controlled fashion.” Since the jaws are located in the gantry head, the scatter dose is significantly reduced. In this study, we look at the differences in dose variation to the contralateral breast when using dyna~c wedges in the medial tangent field compared to an open field and a regular wedged field. What we hope to prove is that the contralateral breast
INTRODUCTION Several studies have shown that breast irradiation following surgical removal of a tumor is not only successful in treating localized breast cancer, it is also equal to surgery in survival and local control rates.‘.2 What is uncertain is the chronic effects that irradiation might have on the tissues surrounding the treatment field, such as the con~~ateral breast.” Studies have shown an increased incidence in secondary cancers in patients who have had radiation treatment to the breast, compared to those who have not had radiation.435 But, these same studies do not show an increased incidence of development of cancers in the contralateral breast. Nevertheless, it has been reported that patients that were irradiated in the chest region at a young age will have a higher incidence of developing breast cancer later in life.4,5*6 This is, among other reasons, because the induction of breast cancer is age and dose dependent.4.5.h.7Since we cannot control the age of the patient, we need to look at reducing the dose outside the treatment field as much as possible. Fraass et al., ’ demonstrated, dough various techniques, different methods to reduce the radiation peripheral dose during treatment. One of these techniques 287
288
Medical Dosimetry
will receive approximately the same amount of dose from the medial tangent field using a dynamic wedge versus an open field. MATERIALS
Volume 20, Number 4, 1995
Tabie 1. Ratio of the peripheral dose for a regular and dynamic wedged field verses an open field Distance from field edge
2.0 cm
10.0 cm
20.0 cm
Dynamic Wedge Regular Wedge
117.8 168.5
120.0 286.9
110.4 297.5
AND METHODS
The study is divided into three phases. First, we measure the peripheral dose outside the treatment field in a tissue equivalent phantom (solid water) ; Second, we use a humanoid phantom to measure the dose received by the con~lateral breast, and third we take measurements on patients. Using a 6 MV linear accelerator, * a fast feedback electrometer with a digital readout,’ a Markus parallel plate chamber, and solid water, we are able to measure the dose to the periphery of the radiation field. The measurements for each treatment technique are taken at perpendicular distances up to 20 cm away from the field edge, and at depths of 0 cm, 1.5 cm, 3.0 cm, and 6.0 cm using a 20 x 10 cm2 (L X W) field size. The measurements are made along the width of the field utilizing 45” regular and dynamic wedges. After taking several readings for each treatment technique, we are able to obtain the percentage of isocentric dose deposited outside the treatment field. In the second phase of the study, we use an anthropomo~hic ph~tom~ fitted with wax breasts. The contralateral breast is designed to hold 38 Thermoluminescent Dosimeters (TLD) which are placed in 3 transverse planes 2 cm apart at depths ranging from O-3.0 cm. There are also 27 TLDs placed inside the phantom itself, the depths here being dependent on the contour of the phantom. The treated breast is designed to hold 2-3 TLDs, which are used to determine the percentage of the isocentric dose at each calculation point. The TLDs that are used in this study contain lithium fluoride (LiF) 100 powder. We estimate the measurement precision of the TLDs to be approximately 55%. At Stanford, we routinely use the National Cancer Institute (N.C.I.) isocentric treatment technique where the medial edge is usually positioned at the mid sagittal plane. The deep edge of the tangents are aligned to be coincident with one another. This technique has been described extensively by Lichter et a1.‘2 The average field size of the tangents are 18 X 8.5 cm2 (L X W) with approximately 1.5 cm of lung tissue within the irradiated field. A transverse CT scan is done to verify the mechanical outline and to provide a means to develop a three dimensional (3D) treatment plan. In this phase of the study, a 30” wedge is used to obtain a better dose distribution than a 45“ wedge. The third phase of the study deals with actual patient measurements which are also ob~ned by using
* Varian 2300CD Linear Accelerator i CNMC-Keithley Electrometer. Model K602 * Alderson Rando Phantom
The values represent the percentage of dose delivered to isocenter at a depth of dmax (1.5 cm)
TLDs. The patients are treated with 6 MV photons utilizing the same t~atment technique as in the phantom study. They are immobilized in an Alpha Cradle@ and setup with or without supraclavicular fields. The treatment plans are designed to have wedging only on the lateral tangent field, thus providing us limited information as to the contralateral breast dose received by wedging the medial tangent field. RESULTS
AND DISCUSSION
As reported in previous studies,8,‘“.14 the most consequential distance in measuring the contralateral breast dose is the perpendicular distance from the field edge. With this distance the gantry angle and the distance following the contour of the breast become less important.x,‘4 Table 1 shows the ratio of the peripheral dose at the depth of m~imum buildup (dmax) using a 45” dynamic and regular wedge compared to the peripheral dose of the open field at distances of 2.0 cm, 10.0 cm, and 20.0 cm from the edge of the field. The signi~cant feature of this table is that the dynamic wedge gives about 20% more dose to the contralateral breast than the open field, but the regular wedge gives approximately 200% to 300% more dose compared to the open field. Figures l-4 show the percentage of dose at various distances from the field edge at depths ranging from 0 cm to 6.0 cm. This dose is normalized at the depth of dmax for each treatment technique, and by normalizing at this depth, the data are independent of the wedge factor, thus providing a fair comparison. Figs. l-4 also show three important features. First, that the surface doses for all three techniques are higher than the doses at depth. Second, as depth increases the contribution of dose to the phantom by the regular wedge will decrease (this is likely to occur because the low energy electrons are being filtered out), although the dose from the dynamic wedge and/or open field does not change significantly. And third, when the perpendicular distance reaches approximately 6.0 cm the dose for each treatment technique remains relatively constant. The contralateral measurements done on the phantom were performed utilizing 30 degree regular and dynamic wedges. Instead of optimizing the isodose
Evaluating
the
Dose
to the Contra
Lateral
Peripheral
dose
Breast
e C. D. WEIDES
289
et nl.
at surface
-e-
45 d%g~ dynamic wedge
x
45 d%g. physical
wedge
16 Distance
(cm) from the field edge (thin end of the wedge)
Fig. 1. The peripheraldoseat the surfaceusinga tissueequivalentphantom(solid water).
0
2
i
lb Distancst
(cm)from
-e-
45
deg.dynamicwedge
-n-
45
deg. regularwedge
Ii
the field edge (thin end of the wedge)
Fig. 2. The peripherat
dose at dmax ( 13 cm).
19
290
Volume 20, Number 4, 1995
PerMetal
dose at 6.0 cm deep
-
+
Open fietd
-a-
46
deg. dynamic wedge c
: t I-
I
4
I , 1
6 lXstance
, 1 8
, , IO
I “I
12
/
14 (cm) from the field edge (thin end of the wedge)
Fig. 4. The peripheratdoseat 6.0 cm in depth.
”
I I
16
”
I 1 “?
18
Evaluating
the Dose to the Contra
Lateral
Breast 0 C. D. WEIDES et al.
Fig. 5. Shows the isodose distribution for a tangential field where the medial field is open, and the lateral field has a 30” dynamic wedge.
Fig. 6. Shows the isodose distribution for a tangential field utilizing a 30” dynamic wedge in both the medial and lateral fields.
292
Medical Dosimetry
Fig. 7. Shows the isodose distribution
for a tangential field utilizing a medial 30” regular wedge and a 30” dynamic wedge on the lateral field.
curve distribution we chose to use the same weighting and isocentric dose for all three techniques, and to allow the comp~son to be ~de~ndent of the wedge factor. The perpendicular distance from the edge of the beam is obtained from the CT scan and ranged from 2.7 cm-12.0 cm. Figures 5-7 show the isodose distribution for the contralateral breast and are normalized to the dose at isocenter. The figures show that for the regular wedge, the con~alater~ breast is receiving about 26% of the dose at isocenter whereas the dynamic wedge gives approximately l-5% with an average dose of about 2.5%. At this time, our clinic policy is to treat breast patients with an open medial field, and a wedged lateral field. Because of this policy we have not performed any in vivo dosimetry to compare with the data from the humanoid phantom study. However the phantom study does indicate that using a dynamic wedge on the medial field would be comparable to an open field technique, but further measurements on patients are needed to confirm this. CONCLUSION Even though dose received to breast i~ad~ation still cases where
Volume 20, Number 4, 1995
there is no data establishing that the the contralateral breast via primary causes secondary cancers, there are a small number of cancers arise in
the contralateral breast.“,5 Several studies have shown that by implementing relatively simple procedures the amount of dose received by the contr~at~ral breast can be significantly reduced during primary breast irradiation.’ Our study shows that if a medial wedge is needed in a treatment plan, using a dynamic wedge would only slightly increase the scatter dose to the opposite breast, compared to the use of a lateral wedge only. Further studies need to be done in regard to patient me~~ements~ and the use of different wedge angles. If the patient and wedge data turn out to resemble the findings from the phantom study, then using the dynamic wedge will be a feasible treatment option.
1. Clark, R.M.; Wilkinson, R.H.; Mahoney, L.J.; Reid, J.G.; MacDonald, W.D. Breast Cancer: a 21 Year Experience with Conservative Surgery and Radiation. ht. J. Radiat. Oncol. Biol. Phys. 8:967-975; 1982. 2. Levitt, S.H.; Potish, R.A. The RoIe of Radiation Therapy in the Treatment of Breast Cancer: Tbe use and abuse of Clinical Trials, Statistics and Unproven Hypotheses. ht. J. Radiat. Oncol. Biol. Phys. 6:791-798; 1980. 3. Kase, K.R.; Svensson. G.K.; Wolbarst, A.B.; Marks, M.A. Measurements of Dose from Secondary Radiation Outside a Treatment Field. ht. J. Rapt. Oncol. Biol. Phys. 9: !177- 1183; 1983. 4. Barat, E.; Larsson, L.E.; Mattsson, B. Breast Cancer following Jrradiation of the Breast. Cancer. 40:2905-2910; 1977. 5. Svensson, G.K.; Kase. K.R.; Chin, L.M.; Harris, J.R. Dose to the Opposite Breast as a ResuIt of Primary Radiation Therapy for Carcinoma of the Breast. ht. J. Radiaf. Oneof. Bid. Phys. 7:1209, 1981. Cancer Institute. 84~124% 1249; 1992.
Evaluating
the Dose to the Contra
6. Boice, J.D. Jr.; Land, C.E.; Shore, R.E.; Norman, J.E.; Tokunaga. M. Risk of Breast Cancer following low-dose Radiation Exposure.’ Radiology. 131:589-597; 1979. 7. Muller-Runkel, R.; Kalokhe, U.P. Method of Reducing Scatter Radiation Dose to the Contralateral Breast during Tangential Breast Irradiation Therapy. Radiology. 191:853-855; 1994. 8. Fraass, B.A.; Robinson, P.L.; Lichter, AS. Dose to the contralatera1 breast due to primary breast irradiation. Int. J. Radiat. Oncol. Biol. Phys. 11:485-497; 1985. 9. Cross, P.; Joseph, D.J.; Cant, J.; Cooper, S.G.; Denham, J.W. Tangential Breast Irradiation: Simple Improvements. Inf. J. Radiat. Oncol. Biol. Phys. 23:433-442; 1992. 0. Leavitt, D.D.; Moeller, J.H.; Stone, A. Reduction of Peripheral Dose by Dynamic Wedge Techniques. Medical Physics. 20:877; 1993.
Lateral
Breast 0 C. D. WEIDES
et al.
293
11. Kijewski, P.K.; Chin, L.M.; Bjamgard, B.E. Wedge-shaped dose distributions by computer-controlled collimator motion. Medical Physics. 5427-429; 1978. 12. Lichter, A.S.; Fraass, B.A.; Geijn, J.; Padikal, T.N. A Technique for Field Matching in Primary Breast Irradiation. Int. .I. Radiar. Oncol. Biol. Ph.ys. 9:263-270; 1983. 13. Fraass, B.A.; Van de Geijn, J. Peripheral dose from megavolt beams. Medical Physics 10(6):809-818; 1983. 14. McParland, B.J. The effect of a Dynamic Wedge in the Medial Tangential Field upon the Contralateral Breast Dose. Inf. J. Radia?. Oncol. Biol. Phys. 19: 15 15- 1520; 1990. 15. Storm, H.H.; Anderson, M.; Boice, J.D.; Blettner, M.; Stovall, M.; Mouridsen, H.T. adjuvant Radiotherapy and Risk of Contralateral Breast Cancer. Journal of the National Cancer Institute. 84:1245-1249: 1992.
Perg~oN
Medical 0 I995
Dosimetry. American
Vol. 20, No. 4, pp. 287-293, 1995 Association of Medical Dosimetrists Printed in the USA. All rights reserved 0958-3947195 $9.50 + .oo
0958-3947(95)02011-X
EVALUATING WHEN USING CHRISTOPHER
THE DOSE TO THE CONT~LATE~L BRIEAST A DYNAMIC WEDGE VERSUS A REGULAR WEDGE
D. WEIDES,
EDWARD
C. ?vkx, WENDY C. CHANG, and CAROL A. SHOSTAK
DAVID
0. FINDLEY,
Stanford University School of Medicine, Department of Radiation Oncology. Stanford, California 94305-5 105 Abstract--The incidence of secondary cancersin the contralateral breast after primary breast irradiation is several times higher than the incidence of first time breast cancer. Studies have shown that the scatter radiation to the contralateral breast may pIay a huge part in the induction of secondary breast cancers. Factors that may contribute to the contralateral breast dosemay include the useof blocks, the orientation of the field, and wedges.Reports have shown that the use of regular wedges,particularly for the medial tangential field, gives a si~ifican~y higher doseto the contralateral breast compared to an openfield. This paper comparesthe peripheral doseoutsidethe field using a regular wedge,a dynamic wedge,and au open field technique. The data colbxted consistedof measurementstaken with patients, solid water and a Rando phantom using a Varian 2300CDlinear accelerator. ion chambers,thermoluminescentdosimeters(TLD) , diodes,and Almswere the primary meansfor collecting the data. The measurementsshowthat the peripheral doseoutside the field using a dynamic wedgeis close to that of open fields, and signiiicantly lower than that of regular wedges.This isolation indicatesthat when usinga medial wedge,a dynamic wedgeshould be used. Key Words:Contralateral,Breast, Dynamic wedge, Dose.
dealt with removing the wedge from the medial tangent field. Other studies also show that the majority of the contralateral breast dose is produced by the medial tangent beam, whereas, the dose from the lateral tangent beam has to transverse through several centimeters of tissue before it reaches the contralateral breast.7.X.‘,‘0 The isodose distribution, with only the lateral wedge, does give an acceptable treatment plan most of the time, but there are still times when a medial wedge would improve the isodose dis~bution throughout the treatment volume. Advances in technology have provided the necessary means to accompIish the goal of reducing the radiation dose to the contralateral breast. A device known as a dynamic wedge should prove to be useful in decreasing the dose and yet maintaining a medial wedge. The dynamic wedge uses the primary collimator jaws to create the wedge effect as it moves across the field in a computer controlled fashion.” Since the jaws are located in the gantry head, the scatter dose is significantly reduced. In this study, we look at the differences in dose variation to the contralateral breast when using dyna~c wedges in the medial tangent field compared to an open field and a regular wedged field. What we hope to prove is that the contralateral breast
INTRODUCTION Several studies have shown that breast irradiation following surgical removal of a tumor is not only successful in treating localized breast cancer, it is also equal to surgery in survival and local control rates.‘.2 What is uncertain is the chronic effects that irradiation might have on the tissues surrounding the treatment field, such as the con~~ateral breast.” Studies have shown an increased incidence in secondary cancers in patients who have had radiation treatment to the breast, compared to those who have not had radiation.435 But, these same studies do not show an increased incidence of development of cancers in the contralateral breast. Nevertheless, it has been reported that patients that were irradiated in the chest region at a young age will have a higher incidence of developing breast cancer later in life.4,5*6 This is, among other reasons, because the induction of breast cancer is age and dose dependent.4.5.h.7Since we cannot control the age of the patient, we need to look at reducing the dose outside the treatment field as much as possible. Fraass et al., ’ demonstrated, dough various techniques, different methods to reduce the radiation peripheral dose during treatment. One of these techniques 287
288
Medical Dosimetry
will receive approximately the same amount of dose from the medial tangent field using a dynamic wedge versus an open field. MATERIALS
Volume 20, Number 4, 1995
Tabie 1. Ratio of the peripheral dose for a regular and dynamic wedged field verses an open field Distance from field edge
2.0 cm
10.0 cm
20.0 cm
Dynamic Wedge Regular Wedge
117.8 168.5
120.0 286.9
110.4 297.5
AND METHODS
The study is divided into three phases. First, we measure the peripheral dose outside the treatment field in a tissue equivalent phantom (solid water) ; Second, we use a humanoid phantom to measure the dose received by the con~lateral breast, and third we take measurements on patients. Using a 6 MV linear accelerator, * a fast feedback electrometer with a digital readout,’ a Markus parallel plate chamber, and solid water, we are able to measure the dose to the periphery of the radiation field. The measurements for each treatment technique are taken at perpendicular distances up to 20 cm away from the field edge, and at depths of 0 cm, 1.5 cm, 3.0 cm, and 6.0 cm using a 20 x 10 cm2 (L X W) field size. The measurements are made along the width of the field utilizing 45” regular and dynamic wedges. After taking several readings for each treatment technique, we are able to obtain the percentage of isocentric dose deposited outside the treatment field. In the second phase of the study, we use an anthropomo~hic ph~tom~ fitted with wax breasts. The contralateral breast is designed to hold 38 Thermoluminescent Dosimeters (TLD) which are placed in 3 transverse planes 2 cm apart at depths ranging from O-3.0 cm. There are also 27 TLDs placed inside the phantom itself, the depths here being dependent on the contour of the phantom. The treated breast is designed to hold 2-3 TLDs, which are used to determine the percentage of the isocentric dose at each calculation point. The TLDs that are used in this study contain lithium fluoride (LiF) 100 powder. We estimate the measurement precision of the TLDs to be approximately 55%. At Stanford, we routinely use the National Cancer Institute (N.C.I.) isocentric treatment technique where the medial edge is usually positioned at the mid sagittal plane. The deep edge of the tangents are aligned to be coincident with one another. This technique has been described extensively by Lichter et a1.‘2 The average field size of the tangents are 18 X 8.5 cm2 (L X W) with approximately 1.5 cm of lung tissue within the irradiated field. A transverse CT scan is done to verify the mechanical outline and to provide a means to develop a three dimensional (3D) treatment plan. In this phase of the study, a 30” wedge is used to obtain a better dose distribution than a 45“ wedge. The third phase of the study deals with actual patient measurements which are also ob~ned by using
* Varian 2300CD Linear Accelerator i CNMC-Keithley Electrometer. Model K602 * Alderson Rando Phantom
The values represent the percentage of dose delivered to isocenter at a depth of dmax (1.5 cm)
TLDs. The patients are treated with 6 MV photons utilizing the same t~atment technique as in the phantom study. They are immobilized in an Alpha Cradle@ and setup with or without supraclavicular fields. The treatment plans are designed to have wedging only on the lateral tangent field, thus providing us limited information as to the contralateral breast dose received by wedging the medial tangent field. RESULTS
AND DISCUSSION
As reported in previous studies,8,‘“.14 the most consequential distance in measuring the contralateral breast dose is the perpendicular distance from the field edge. With this distance the gantry angle and the distance following the contour of the breast become less important.x,‘4 Table 1 shows the ratio of the peripheral dose at the depth of m~imum buildup (dmax) using a 45” dynamic and regular wedge compared to the peripheral dose of the open field at distances of 2.0 cm, 10.0 cm, and 20.0 cm from the edge of the field. The signi~cant feature of this table is that the dynamic wedge gives about 20% more dose to the contralateral breast than the open field, but the regular wedge gives approximately 200% to 300% more dose compared to the open field. Figures l-4 show the percentage of dose at various distances from the field edge at depths ranging from 0 cm to 6.0 cm. This dose is normalized at the depth of dmax for each treatment technique, and by normalizing at this depth, the data are independent of the wedge factor, thus providing a fair comparison. Figs. l-4 also show three important features. First, that the surface doses for all three techniques are higher than the doses at depth. Second, as depth increases the contribution of dose to the phantom by the regular wedge will decrease (this is likely to occur because the low energy electrons are being filtered out), although the dose from the dynamic wedge and/or open field does not change significantly. And third, when the perpendicular distance reaches approximately 6.0 cm the dose for each treatment technique remains relatively constant. The contralateral measurements done on the phantom were performed utilizing 30 degree regular and dynamic wedges. Instead of optimizing the isodose
Evaluating
the
Dose
to the Contra
Lateral
Peripheral
dose
Breast
e C. D. WEIDES
289
et nl.
at surface
-e-
45 d%g~ dynamic wedge
x
45 d%g. physical
wedge
16 Distance
(cm) from the field edge (thin end of the wedge)
Fig. 1. The peripheraldoseat the surfaceusinga tissueequivalentphantom(solid water).
0
2
i
lb Distancst
(cm)from
-e-
45
deg.dynamicwedge
-n-
45
deg. regularwedge
Ii
the field edge (thin end of the wedge)
Fig. 2. The peripherat
dose at dmax ( 13 cm).
19
290
Volume 20, Number 4, 1995
PerMetal
dose at 6.0 cm deep
-
+
Open fietd
-a-
46
deg. dynamic wedge c
: t I-
I
4
I , 1
6 lXstance
, 1 8
, , IO
I “I
12
/
14 (cm) from the field edge (thin end of the wedge)
Fig. 4. The peripheratdoseat 6.0 cm in depth.
”
I I
16
”
I 1 “?
18
Evaluating
the Dose to the Contra
Lateral
Breast 0 C. D. WEIDES et al.
Fig. 5. Shows the isodose distribution for a tangential field where the medial field is open, and the lateral field has a 30” dynamic wedge.
Fig. 6. Shows the isodose distribution for a tangential field utilizing a 30” dynamic wedge in both the medial and lateral fields.
292
Medical Dosimetry
Fig. 7. Shows the isodose distribution
for a tangential field utilizing a medial 30” regular wedge and a 30” dynamic wedge on the lateral field.
curve distribution we chose to use the same weighting and isocentric dose for all three techniques, and to allow the comp~son to be ~de~ndent of the wedge factor. The perpendicular distance from the edge of the beam is obtained from the CT scan and ranged from 2.7 cm-12.0 cm. Figures 5-7 show the isodose distribution for the contralateral breast and are normalized to the dose at isocenter. The figures show that for the regular wedge, the con~alater~ breast is receiving about 26% of the dose at isocenter whereas the dynamic wedge gives approximately l-5% with an average dose of about 2.5%. At this time, our clinic policy is to treat breast patients with an open medial field, and a wedged lateral field. Because of this policy we have not performed any in vivo dosimetry to compare with the data from the humanoid phantom study. However the phantom study does indicate that using a dynamic wedge on the medial field would be comparable to an open field technique, but further measurements on patients are needed to confirm this. CONCLUSION Even though dose received to breast i~ad~ation still cases where
Volume 20, Number 4, 1995
there is no data establishing that the the contralateral breast via primary causes secondary cancers, there are a small number of cancers arise in
the contralateral breast.“,5 Several studies have shown that by implementing relatively simple procedures the amount of dose received by the contr~at~ral breast can be significantly reduced during primary breast irradiation.’ Our study shows that if a medial wedge is needed in a treatment plan, using a dynamic wedge would only slightly increase the scatter dose to the opposite breast, compared to the use of a lateral wedge only. Further studies need to be done in regard to patient me~~ements~ and the use of different wedge angles. If the patient and wedge data turn out to resemble the findings from the phantom study, then using the dynamic wedge will be a feasible treatment option.
1. Clark, R.M.; Wilkinson, R.H.; Mahoney, L.J.; Reid, J.G.; MacDonald, W.D. Breast Cancer: a 21 Year Experience with Conservative Surgery and Radiation. ht. J. Radiat. Oncol. Biol. Phys. 8:967-975; 1982. 2. Levitt, S.H.; Potish, R.A. The RoIe of Radiation Therapy in the Treatment of Breast Cancer: Tbe use and abuse of Clinical Trials, Statistics and Unproven Hypotheses. ht. J. Radiat. Oncol. Biol. Phys. 6:791-798; 1980. 3. Kase, K.R.; Svensson. G.K.; Wolbarst, A.B.; Marks, M.A. Measurements of Dose from Secondary Radiation Outside a Treatment Field. ht. J. Rapt. Oncol. Biol. Phys. 9: !177- 1183; 1983. 4. Barat, E.; Larsson, L.E.; Mattsson, B. Breast Cancer following Jrradiation of the Breast. Cancer. 40:2905-2910; 1977. 5. Svensson, G.K.; Kase. K.R.; Chin, L.M.; Harris, J.R. Dose to the Opposite Breast as a ResuIt of Primary Radiation Therapy for Carcinoma of the Breast. ht. J. Radiaf. Oneof. Bid. Phys. 7:1209, 1981. Cancer Institute. 84~124% 1249; 1992.
Evaluating
the Dose to the Contra
6. Boice, J.D. Jr.; Land, C.E.; Shore, R.E.; Norman, J.E.; Tokunaga. M. Risk of Breast Cancer following low-dose Radiation Exposure.’ Radiology. 131:589-597; 1979. 7. Muller-Runkel, R.; Kalokhe, U.P. Method of Reducing Scatter Radiation Dose to the Contralateral Breast during Tangential Breast Irradiation Therapy. Radiology. 191:853-855; 1994. 8. Fraass, B.A.; Robinson, P.L.; Lichter, AS. Dose to the contralatera1 breast due to primary breast irradiation. Int. J. Radiat. Oncol. Biol. Phys. 11:485-497; 1985. 9. Cross, P.; Joseph, D.J.; Cant, J.; Cooper, S.G.; Denham, J.W. Tangential Breast Irradiation: Simple Improvements. Inf. J. Radiat. Oncol. Biol. Phys. 23:433-442; 1992. 0. Leavitt, D.D.; Moeller, J.H.; Stone, A. Reduction of Peripheral Dose by Dynamic Wedge Techniques. Medical Physics. 20:877; 1993.
Lateral
Breast 0 C. D. WEIDES
et al.
293
11. Kijewski, P.K.; Chin, L.M.; Bjamgard, B.E. Wedge-shaped dose distributions by computer-controlled collimator motion. Medical Physics. 5427-429; 1978. 12. Lichter, A.S.; Fraass, B.A.; Geijn, J.; Padikal, T.N. A Technique for Field Matching in Primary Breast Irradiation. Int. .I. Radiar. Oncol. Biol. Ph.ys. 9:263-270; 1983. 13. Fraass, B.A.; Van de Geijn, J. Peripheral dose from megavolt beams. Medical Physics 10(6):809-818; 1983. 14. McParland, B.J. The effect of a Dynamic Wedge in the Medial Tangential Field upon the Contralateral Breast Dose. Inf. J. Radia?. Oncol. Biol. Phys. 19: 15 15- 1520; 1990. 15. Storm, H.H.; Anderson, M.; Boice, J.D.; Blettner, M.; Stovall, M.; Mouridsen, H.T. adjuvant Radiotherapy and Risk of Contralateral Breast Cancer. Journal of the National Cancer Institute. 84:1245-1249: 1992.