Arms Positioning Effect on Dose Distribution in Target and Organs at Risk in Breast Radiotherapy after Breast-Conserving Surgery

Purpose: Breast cancer is the second most common cancer in women. This study aims to evaluate the effect of the patient’s arm positioning on dose distribution in Planning Target Volume (PTV) and Organs At Risk (OARs) in radiotherapy after Breast-Conserving Surgery (BCS). Materials and Methods: Thirty patients were divided into two groups; each group included 15 patients, including those in the left arm-up position (group 1) and both arms-up positions (group 2). The patients were selected randomly, and both groups were planned based on 16-slice Computed Tomography (CT) with a 5 mm slice thickness. The patients had been treated with 6 MV photon beam energy at the prescribed dose of 50 Gy in 25 fractions, and planning was performed using the Monaco Treatment Planning System (TPS). The results of dose parameters for the PTV, such as minimum dose (Dmin), mean dose (Dmean), maximum dose (Dmax), Heterogeneity Index (HI), and Conformity Index (CI), were obtained. For OARs, dose parameters such as Dmin, Dmean, and Dmax were calculated. TCP for tumors and NTCP for OARs were also evaluated as radiobiological parameters. Results: There was no statistically significant difference between the two groups in terms of dose parameters in PTV, but there was a difference for the OARs, such as thyroid. Conclusion: The patient's arm position significantly affects the dose distribution for OARs such as the thyroid (p<0.05), and the position of both arms up (group 2) is relatively better than the left arm up (group 1) due to some clinical reasons.