A comparison of contralateral breast dose due to breast cancer radiotherapy using two different treatment machines in a radiotherapy center

Background: The radiation dose received by contralateral breast (CLB) is one of the concerns of breast radiotherapy, because it may lead to the induction of secondary breast cancer. The aim of this study was to evaluate the CLB surface dose in the breast treatment in Yazd radiotherapy center. Materials and Methods: The surface dose of CLB was measured using TLD dosimetry in 50 cancer breast patients. The TLD chips were placed at four points on the each of CLBs. The patients were treated by 6MV photon beams of Oncor (physical wedge) and Compact (motorized wedge) LINAC. The TLD chips were placed on the surfaces of CLB during the medial and lateral tangent radiation fields in one of radiotherapy fractions. Results: The mean percent of prescription dose of the CLB surface doses on the point 1 in the two Linac (Oncor & Compact) were significantly different. The mean of CLB surface doses of point 1 in the physical and the motorized wedge techniques were 5.78 and 7.84 percent of prescription dose of breast cancer, respectively. The medial and lateral fields' contribution from 7.4% surface dose of CLB were 5.8% and 1.6%, respectively. Conclusion: In Shahid Ramezanzadeh radiotherapy center, the CLB surface dose due to breast cancer radiotherapy by the Compact machine (7.84 %) was significantly more than the allowable value (6% prescription dose). The CLB does due to the medial field beam was more than the lateral field.