Gantry-Based Pencil Beam Scanning (PBS) Proton Therapy for Uveal Melanoma: IMPT Versus Proton Arc Therapy

Document Type

Conference Proceeding

Publication Date

3-2025

Publication Title

International Journal of Particle Therapy

Abstract

Purpose: This study reports PBS-based multi-field IMPT for uveal melanoma in a standard gantry room. We hypothesize that PBS proton arc therapy(pArc) can offer superior or equivalent plan quality compared to IMPT. Methods: We treated 11 uveal melanoma patients with IMPT, delivering 50Gy in 5-fractions. A customized gaze-fixation device attached to the thermoplastic mask was employed for each patient to ensure consistent alignment. The IMPT plan was robustly optimized to account for 3mm setup and 3.5% range uncertainties using 3-4 fields without apertures. Each plan was reoptimized with the same robust settings using two non-coplanar arcs, purposely avoiding anterior beams to minimize dose to the anterior eye, eliminate the use of an eye retractor, and reduce potential range uncertainty induced by the eyelid. Plan delivery was evaluated based on the daily CBCTs. Plan quality was assessed with metrics including target coverage and mean/maximum doses (Dmean/Dmax) to the organsat-risk(OARs). Results: Both pArc and IMPT achieved similar target coverage, with D95% equal to 101.4%±0.4% and 101.1%±1.0%, respectively. The pArc provided a better conformity index(RTOG) of 0.95 ±0.23 compared to 0.88±0.18 with IMPT(p>0.05). Both plans consistently met the clinical objectives for OARs. Notably, pArc reduced the retina Dmax from 54.5±0.7 to 53.2±0.3Gy(p< 0.05). Treatment evaluation indicated that the delivered dose was consistent with the planned dose, with a relative difference of D95% within 3.5%(IMPT) and 3.1%(pArc), and actual delivery exceeding 98.7%(IMPT) and 98.2%(pArc). Conclusions: PBS-based IMPT for ocular cancer was successfully implemented. This study demonstrated that a two-field non-coplanar pArc plan can deliver comparable dosimetric metrics to IMPT plans.

Volume

15

Issue

Supple

First Page

100683

Last Page

100683

Comments

10th Annual Conference of the Particle Therapy Cooperative Group - North America (PTCOG_NA), November 14-16, 2024, New York City, NY

DOI

10.1016/j.ijpt.2024.100683

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