Room: AAPM ePoster Library
Purpose: To investigate the feasibility and the clinical benefit of using a 2-beams approach in ocular clipless proton therapy with a fixed horizontal eye line using a 4Pi optimization based on beam-eye-view overlap of tumor and organs-at-risk (OARs).
Methods: An in-house developed ocular melanoma proton treatment planning system (TPS) was used to calculate dose distributions on 3D MRI-based reconstructed eyes. Five uveal melanoma patients were included in the study. High-resolution 3D MRI images were acquired on a 7T Philips Achieva MRI (Best, The Netherlands). Target volume and OARs were semi-automatically delineated, including optic nerve, ciliary body, lens and sclera ring. The macula was geometrically defined as it is not visible on MRI. A previously published 4Pi beam angle optimization algorithm was modified for the purposes of ocular proton therapy to determine optimal gazing angles. This optimizer, based on beams-eye-view overlap between tumor and OARs, calculated two optimal gazing angles within a clinically feasible space (±30° upward/downward, ±30° left/right). Dose calculations were performed for the gazing angles optimally selected by 4Pi, resulting in a two equally-weighted beams plan vs. two individual beam plans. Dosimetric outcomes were extracted from each plan to evaluate which approach was more favorable for OARs sparing.
Results: Among the patients of our cohort, the mean dose to OARs was reduced by 8.3% on average by using a 2-beams approach. An overall mean dose to OARs decrease of 6.3% and 10.3% was achieved on average with the 2-beams configuration vs. the single beam 1 and single beam 2 configuration, respectively.
Conclusion: This work confirms that using more than one beam in ocular proton therapy yields a better trade-off in OARs sparing. It also shows the usefulness of an automated and objective method applied to gaze angle selection using a 4Pi beam angle optimization approach.
Funding Support, Disclosures, and Conflict of Interest: This research was co-founded by the research program PROTONS4Vision (Grant NWO 14654), which is financed by the Netherlands Organization for Scientific Research (NWO), Technology Foundation STW, the Top consortium for Knowledge & Innovation (TKI-HTSM) and Varian Medical Systems, Inc., Palo Alto.