Room: AAPM ePoster Library
Purpose: Accelerated Partial Breast Irradiation (APBI) commonly uses 3D-conformal radiation therapy (3D-CRT). Halcyon offer faster gantry rotation and MLC movement compared to Truebeam®. Utilizing Halcyon, we investigated whether VMAT will result in greater conformity index (CI), greater of sparing of normal breast tissue, and shorter treatment times relative to 3D-CRT for APBI treatment.
Methods: Ten APBI patients previously treated with 3D-CRT APBI with mixed beams (6-18MV) on Truebeam® had plans re-optimized in Eclipse treatment planning system via Photon Optimizer (Version 15.6) to simulate Halcyon treatments. Final dose calculations were performed with advanced AcurosXB algorithm. Halcyon plan angles were chosen to cover the planning target volume (PTV) and avoidance sectors were utilized to minimize dose to lung. RTOG-0413 guidelines were followed for PTV coverage and organs at risk (OAR) dose limits.
Results: Halcyon plans had greater conformity compared to the 3D-CRT plans with better CI (p<0.001). The average CI for Halcyon and 3D-CRT plans were 0.99±0.02 (0.96-1.02) and 1.39±0.23 (1.17-1.86), respectively.The normal breast V50%(p=0.002), V80%(p=0.001), and V100%(p=0.009) were significantly lower with all the Halcyon plans. Treatment time was shortened on Halcyon: 0.84±0.18 minutes (0.6-1.1 min) and 1.0±0.19 minutes (0.8-1.23 min). However, despite meeting RTOG-0413 guidelines, Halcyon had higher mean values of heart V5% [108.9±82.4 cc (3.9-224.2 cc) vs 12.4±9.1 cc (0-25.8 cc)] and ipsilateral lung V30%, [136.2±106.1 cc (20.4-367.4 cc) vs 106.9±95.9 cc (7.5-307.2 cc)], respectively.
Conclusion: Halcyon APBI plans produced more conformal PTV dose distributions and delivered less dose to normal ipsilateral breast, compared to 3D-CRT plans. Doses to the OAR increased slightly compared to the 3D-CRT plans but still met RTOG 0413 limits. This indicates Halcyon can deliver APBI with better CI and less dose to the normal breast resulting in potential greater cosmetic outcomes and can be offered treatment to APBI patients in the Halcyon Linac only clinic.