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Combining Dynamic Wave Arc and Tangential Arc for Breast Boost Irradiation with the Vero System

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M BULETEANU1,2*, T Reynders1, D Verellen1, T Depuydt1, T Gevaert1, K Poels1, M Duchateau1, H Van Parijs1, V Simon2, M Mark De Ridder1, (1) Universitair Ziekenhuis Brussel, Brussels, (2) Babes-Bolyai University, Cluj-Napoca,

SU-E-J-166 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 +/-185⁰. Unlike C-arm gantries it can also rotate around the vertical axis (+/-60⁰). 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.

Funding Support, Disclosures, and Conflict of Interest: 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.

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