SU-E-J-166: Combining Dynamic Wave Arc and Tangential Arc for Breast Boost Irradiation with the Vero System

Purpose: To present two novel treatment planning techniques developed for breast boost irradiation on the Vero system and investigate possible dosimetric advantages. Methods: The Vero system consists of a 6MV LINAC mounted on an O‐ring gantry that rotates around the patients by +/− 185°. Unlike C‐arm gantries it can also rotate around the vertical axis (+/− 60°). A preliminary version iPlan RT (Brainlab AG, Feldkirchen, Germany) was used to plan, optimize and investigate two arc‐based approaches. The Dynamic Wave Arc (DWA) combines simultaneously gantry and ring rotation, offering additional range of treatment orientation without involving patient/couch motion. The Tangential Arc (TGA), static gantry position with continuous ring rotation makes the most of the tangential benefits within the non‐coplanar delivery. Ten patients previously treated for breast boost (7–10 non‐coplanar static beams on Vero) were selected for breast boost comparison. All patients were replanned using two TGA combined with a DWA to achieve a sculpted dose around the thorax wall. The dosimetric parameters were calculated to evaluate the plan quality. Results: The combination of 2TGA and DWA proved to be a feasible technique for breast boost irradiation. In contrast with 3D‐CRT, it presented a better low dose reduction for the V5% and V15% ipsilateral lung. For the left side localizations, the TGA&DWA significantly reduced the heart doses (0.19+/− 0.5 vs. 8.4+/−17.73), the V5% being outside the heart in all cases. A better conformity index was also achieved (0.74 +/−0.03 for TGA&DWA versus 0.67 +/−0.04 for 3D‐CRT). The mean total number of Monitor Units was comparable for both planning approaches. Conclusion: TGA and DWA are two promising techniques that highlight the advantages of the unique design of the Vero system. Combining TGA&DWA already presented good results for breast boost. The dosimetric and clinical gains are to be further investigated for other sites. M. Buleteanu is a PhD student financially supported by Brainlab AG (Feldkirchen, Germany) during the entire period of the doctoral thesis. The other authors have no conflict of interest.