Organ at risk dose measurements following radiotherapy treatment for breast cancer patients

Abstract

Radiotherapy technologies are one of the most common treatments for cancer, they have been successfully used to damage cancer cells, with as little harm as possible to nearby healthy cells, however Secondary cancer risk following radiotherapy is an increasingly important topic in clinical oncology with impact on treatment decision making and on patient management. The objective of this study is to measure the skin radiation dose received by the treated breast as well as the dose to the lungs in cancer patients undergoing breast radiotherapy and estimate the probability for radiation-induced cancer, i.e. secondary cancer and the probability of lung cancer. Usage of RANDO phantoms and GafChromic dosimetry films to do dose measurements during breast radiotherapy. Measured dose and calculated organ dose from patients were compared. The calculated doses were done using the effective dose formula. Measured point doses of both lungs were compared to those calculated by TPS (treatment planning system). Relative Risk (RR) and Probability of Causation (PC) of lungs- probability of cancer- were calculated from patient’s mean doses to the organs (right lung and left lung) using the model described in BEIR V report. RR mean values were 1.278 and 1.032 for ipsilateral and contralateral lungs respectively. In addition, PC mean values were 20.93 % and 3.099% for ipsilateral and contralateral lungs respectively. Breast cancer patients are susceptible to an increased risk of secondary cancer of ipsilateral lungs more than in the contralateral ones.