A Study on Dose Distribution using Virtual Wedge in Breast Cancer

Kim, Sung Kyu; Yun, Sang Mo

Abstract

In the radiation therapy for breast cancer patients, wedge shaped compensators are essentially used to achieve appropriate dose distribution because of thickness difference according to breast shapes. Tangential irradiation technique has usually been applied to radiation therapy for breast cancer patients treated with breast conservative surgery. When a primary beam is incident on wedge shaped compensators from medial direction in tangential irradiation technique, low energy scattered radiation is generated and gives additional dose to the breast surface. As a method to reduced additional dose to breast surface, the use of virtual wedge shaped compensator is possible. Eclipse radiation treatment planning (RTP) systems installed at our institution have virtual wedge shaped compensator for radiation therapy treatment planning. The dose distributions of 15, 30, 45, 60 degree physical wedges and virtual wedges were measured and compared. Results showed that there was no significant differences in symmetry of 10 x 10 field among various wedge angles. When the transmission factor was compared, transmission factor increased linearly as the wedge angle increased. These results indicates that the application of virtual wedge in clinical use is appropriate.