MONOISOCENTRIC VERSUS DIISOCENTRIC HYPOFRACTIONATED ADJUVANT RADIOTHERAPY FOR BILATERAL BREAST CANCER: COMPARATIVE EVALUATION OF HEART AND LUNG DOSES

Abstract

Background: Among cancers that affect women, breast cancer is one of the most common types, comprising around 2% of all breast cancer patients as bilateral breast cancer (BBC). In the treatment of bilateral breast cancer, there is a high challenge in terms of the larger treatment volume and reducing the radiation to the healthy tissues adjacent to it. This makes radiation treatment in BBC challenging compared to treatment in unilateral breast cancer. Although VMAT technique provides precise dose delivery, it needs to be examined in various methods when applied in BBC treatment. Methods: In this research, there were ten bilateral breast cancer patients (BBC) who had modified radical mastectomy surgery (MRM). CT scans of all the patients were performed using GE Optima machine with a 5 mm slice thickness in a supine position and raised arms using active breathing coordinate (ABC). The planning target volume (PTV) and organs at risk (OARs) were delineated by clinicians according to the RTOG guidelines. Treatment plans were created by the Elekta Versa HD machine using the Monaco Treatment Planning System, version 6.00.01. In this research, 40 Gy in 15 fractions with 6 MV energy was used as a prescribed dose. The aim was to deliver the prescribed dose in such a way that at least 95% of the PTV would receive 95% of the prescribed dose with keeping the maximum dose to less than 107%. Dose constraints for the OARs according to the QUANTEC guidelines were taken into account for lung doses (Dmean, V5Gy, V20Gy) and heart doses (Dmean, V25Gy, V30Gy). The dosimetric plans were assessed using DVH, conformability index (CI), and homogeneity index (HI). Results: The coverage of targets (V95) for ISO2 and ISO1 was observed to be the same; however, ISO2 resulted in a significant decrease in hot spots (V105) with p = 0.0001. A reduced dose was given with ISO2 to the lungs and heart with p < 0.001, accompanied by improved conformity index (CI) and homogeneity index (HI). Monitor Units were increased only slightly using ISO2, which was statistically insignificant.