Purpose: To characterize scatter dose, as a function of depth and off‐axis distance, on the contralateral breast (CB), during treatment of ipsilateral breast cancer using 6 and 18MV photon beams, utilizing wedge techniques and IMRT. Method and Materials: A 30×30×30 solid water phantom was utilized to simulate dose delivery to a right ipsilateral breast. Both surface dose measurements and planar dose distributions at depths (d = 1cm and d = 2cm) were analyzed, as well as dose distributions along the transverse axis of the phantom perpendicular to the beam. Data was taken using EDR2 film, thermal‐luminescent dosimeters, and MOSFET detectors. A Varian 2100CD linear accelerator was used. Measurements were performed for the following arrangements: open field (8×18cm2), 30 and 45° physical wedge, 30 and 45° Enhanced Dynamic Wedge (EDW), and control points (CP) used in IMRT. Results: Analysis of the data shows that for the hard wedges used, a significant increase in scatter dose to the CB during treatment by 5–7% and 12–15% for the 6MV and 18MV respectively is present. At a depth of 1 cm (6MV), data indicates that for a position in the CB, scatter dose is approximately 7% of the central axis dose of the open beam. The relative increase of 2% occurred with the use of EDW. No increase in scatter dose was measured for the CP case. Conclusion: This study seems to indicate that it may be possible to quantify scatter dose through a mathematical function, based on beam energy, depth of treatment, and treatment modality. Application of such a function may be of benefit in improving treatment plans and providing guidelines with regard to dose delivery and potential shielding of CB during whole or partial breast radiotherapy.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging