SU‐E‐T‐433: Field‐In‐Field Irradiation for Breast Cancer with VERO‐4DRT System: A Feasibility Study

Abstract

Purpose:The Vero‐4DRT system is a dedicated system for high precision radiation therapy. However, the field size is limited at 15 cm × 15 cm and shapes by using multi‐leaf collimator (MLC) without X‐Jaw and Y‐Jaw. Therefore VERO‐4DRT system is not available to simple wedged irradiation for breast cancer. In this study, we suppose FIF with ring and/or tilt/pan angles whole breast irradiation (FIFWBI). The purpose of this study is to verify the feasibility of FIFWBI with VERO‐4DRT system.Methods:As fundamental evaluation, we performed commissioning test with phantom. The absorbed dose evaluation at several reference points and dose distribution including split area were performed. We planned 10 demonstrative shapes in phantom for measuring these contents with i‐plan workstation (BrainLAB). As clinical evaluation, the dose distribution and dose indexes were evaluated with actual patient data. Five patients with breast cancer were designed FIFWBI radiotherapy plan with split fields. Then, the dose distribution and dose indexes (including Dmax, Dmin, D95, D5 and Homogeneity index) were evaluated in these plans.Results:As the results of fundamental evaluation, all absorbed dose errors between calculated and measured doses were within 2%. The gamma passing rates with 2 mm/3% criteria in all cases were 96±2%. As the results of clinical evaluation, the values of Dmax, D95, D50, D5, and Homogeneity Index were 41.7±0.90 Gy, 49.4±0.34 Gy, 52.26±0.24 Gy, and 1.39±0.03, respectively. For Japanese breast cancer patients, this technique was feasible. However, the large split region was happened in FIFWBI in case of patient with large breast.Conclusion:We evaluated the FIFWBI technique with VERO‐4DRT system. This technique is feasible for Japanese patients, but the patient with large breast should be disagreed with this technique.