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Dynamic Conformal Sub-Arc Vs VMAT Planning for SBRT Lung Treatment

C Yount

C Yount1*, B Sintay1, D Wiant1, J Pursley1, J Terrell1, J Maurer1, A Baydush2, (1) Cone Health Cancer Center, Greensboro, NC, (2) Wake Forest Univ School of Medicine, Winston-salem, NC

SU-E-T-426 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Dynamic conformal arc (DCA) techniques offer many advantages for thoracic stereotactic body radiotherapy (SBRT) compared to VMAT, including the elimination of interplay effect between machine and target motion and increased treatment efficiency. Despite these advantages, DCA techniques are underutilized. One potential explanation for the limited DCA use is the perceived restricted user control on dose rate and conformality. We present a method for DCA planning that divides a full arc into sub-arcs to provide better dose optimization.

Methods: Thoracic SBRT patients were simulated free-breathing and a 4DCT was acquired and binned into ten phase-based scans to determine internal target volumes. Dynamic conformal sub-arc (DCSA) and VMAT plans were created on the free-breathing scan such that at least 95% of the planning target volume received the prescribed dose. For DCSA plans, IMRT-like dose modulation was achieved by varying field weights and angle ranges for each arc to optimize dose rate and conformality. Plans for five patients were created with DCSA and VMAT. Dose metrics including ratios of prescription dose and 50% isodose to PTV volume, volume of dose outside the PTV receiving >105% of the prescription, maximum dose at 2cm from the PTV and volume of lung receiving 20Gy were measured and compared to assess DCSA and VMAT plan quality.

Results: DCSA delivery offers reduced treatment time of up to a factor of 2. Although the conformity index was closer to the ideal value of 1 for all VMAT plans, conformity is also clinically acceptable with DCSA plans. Lung V20% is also comparable and in one case is lower for the DCSA technique.

Conclusion: DCSA delivery techniques are an excellent alternative to VMAT for thoracic stereotactic radiotherapy.

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