Effect of Breathing on Contralateral Breast Doses in Patients with Breast Carcinoma Receiving Radiotherapy

Abstract

ABSTRACT Objectives: Radiotherapy (RT) for breast cancer results in scattered radiation doses to the contralateral breast (CB) which is found to be associated with an increased risk of secondary malignancy. This study investigates the dosimetric and volumetric changes in CB as a consequence of changes during the breathing cycle. Patients- Methods: Ten patients with breast carcinoma underwent breast conservative surgery or mastectomy receiving RT are included. For this study, planning CT (computerized tomography) images were obtained during deep inspiration (I) and end of expiration (E), as well as free breathing (FB) in order to simulate respiratory cycle. I and E images were registered to FB. Targets and CB were contoured by the same Radiation Oncologist on 3 image series. Three dimensional conformal or IMRT planning was done to obtain dose - volume information. Treatment plans and dose calculations were constructed using CT images taken during FB. Then, plan was exported to I and E image series. The significance of dose and volume changes was investigated. Results: Mean breast doses changed marginally between FB and I (p=0,057) while not significant between FB and E (p=0.58). There was a significant variation between I and F, and I and E for 1% of CB volume receiving maximum dose (p=0.008 and p=0.03) while it was not significant between FB and E (p=0.35). Intended dose constrains for CB were achieved for all patients as mean CB doses were less than 1 Gy and max CB doses were less than 3.5 Gy. However, these limitations exceeded during I phase in 6 out of 10 patients regarding maximum CB doses and 1 out of 10 patients for mean CB dose. Conclusion: Contralateral breast dose changes should be considered together with heart and lung dose changes during the different phases of respiratory cycle because maximum CB dose could exceed the upper limit in 60% of patients during I.