SU-E-T-749: Effect of Different Optimization Techniques on Interstitial Breast Brachytherapy

Abstract

Purpose: Purpose of this study is to compare the three doseoptimization techniques based on basal point, target dose point and inverse planning simulated annealing (IPSA) for flexible interstitial breast implant. Methods: Five carcinoma breast patients implanted with the flexible catheters (double plane, triangular geometry) were studied. After CT scan acquisition, clinical target volume (CTV), Organ at risks (OAR) such as lung and heart (in case of left breast) were delineated. Three plans were made for all the patients based on basal dose point, target dose point and IPSA using Nucletron Plato BPS (V3.5.1) planning system. All the plans were evaluated using following indices: Coverage Index (CI), External Volume Index (EI), Homogeneity Index (HI), Overdose Index (OI) and Conformity Index (COIN). For OAR lung and heart maximum dose(dose received by 1cc volume) was noted. Maximum dose to the skin was analyzed visually. Results: The CI (0.9049±0.024, 0.8920±0.015, and 0.96037±0.009), EI (0.1146±0.088, 0.1869±0.077, and 0.1985±0.064), HI (0.4128±0.079, 0.3482±0.080, and 0.3780±0.096), OI (0.2777±0.085, 0.3564±0.059, 0.2529±0.052) and COIN (0.8077±0.081, 0.7385±0.031, and 0.7969±0.041) were shown for basal dose point, target dose point and IPSA based plan respectively. The average of the maximum dose received by the ipsilateral lung is 892.8±378.8, 961.6±545.4 and 812.6±341.6 cGy for basal dose point, target dose point and IPSA based plan respectively. The average of the maximum dose received by heart 625.8±524.2, 687.2±712.8 and 580.0±391 cGy for basal dose point, target dose point and IPSA based plan respectively. Conclusions: IPSA plan showed better target coverage followed by basal dose point and target dose point based plans. Lesser doses of heart and lung volumes were observed for IPSA. For skindoses, no significant difference was found. Even though the classical basal dose point plan was slightly inferior to IPSA, it is easy to plan with the lesser resources.