194 Radiation therapy of breast carcinoma: Confirmation of prescription dose

Abstract

The purpose of this study is quantitation of dose delivered during tangential breast radiation therapy and measurement of scatter dose to the contralateral breast for three different breast set-up techniques. A commercial semi-conductor diode system is used for dose measurements. In-vivo dose measurements on 11 patients undergoing tangential breast radiation therapy with 6 MV photons were performed. Scatter doses to the contralateral breast for three breast set-up techniques were measured and documented as a function of distance from the field edge and various beam modifiers commonly used in breast radiation therapy. The in-phantom measurements resulted in dose accuracy within ± 1.5%. Dose measurements on patients resulted in standard deviations of 1.2%, 2.3% for the medial entrance exit doses and 1.7%, 2.2% respectively for the lateral entrance, exit doses. In patients, the scatter doses to the opposite breast at a 5 cm perpendicular distance from the medial field edge resulted in cumulative scatter doses of 247 cGy to 530 cGy from the tangential fields and an additional 50 cGy from the supraclavicular or axillary field if included. Quantitative verification of the prescribed daily dose is important in breast radiation therapy to ensure precision in patient set-up and accuracy in dose delivery.