SU‐E‐T‐475: Dynamic Conformal Sub‐Arc Vs 3D Planning for SBRT Lung Treatment

Abstract

Purpose: To introduce and compare dynamic conformal sub‐arc (DCSA) planning to static 3D planning for SBRT lung treatments. Methods: Discussions about standard dynamic conformal arcs revealed little control to adjust the dose cloud. This was especially relevant in areas such as a tumor in between the chest wall and lung. DCSA was devised to overcome this lack of adjustability. DCSA reduces an arc field into multiple conformal sub‐arcs, which can then be adjusted using field weights to alter dose contribution and shift the dose cloud. In this initial study, we investigated two DCSAs, where each sub‐arc covered 45°: 8‐field 360° DCSA and 6‐field 270° DCSA. The 360° plans used the fit and shield tool in Eclipse for any field that entered through the spine. The 270° partial arc plans were positioned to have no entry dose into the spine or contralateral lung. These DCSA plans were compared to static 3D SBRT plans for isodose and RTOG dosimetric measurements. Results: Results show minimal differences with the largest differences being a slight increase in volume of the 50% isodose coverage. 360° DCSA plans showed similar MU versus 3D, while 270° DCSA plans showed reduced MU. All organs‐of‐interest doses were significantly below RTOG criterion. The 3D plans incorporated 3 couch kicks, while the DCSA plans had none. Treatment time for the 3D plans was approximately 20–30 minutes because of the couch kicks and repeat imaging, while the DCSA plans can be treated in under 4 minutes at 600 MU/min and beam automation on a Varian Truebeam linac. Isodose comparisons are presented, as well. Conclusion: Full arc DCSA and partial arc DCSA offer comparable treatment plans to 3D planning but can be delivered much more efficiently. This reduces patient treatment time, alleviates the need for any second CBCT localization, removes couch kicks, and may reduce overall MU.