A Modiri¹*, S Mossahebi¹, P Mohindra¹, A Sawant¹, S Chen¹, R Miller², B Zhang¹, B Yi¹, (1) University of Maryland School of Medicine, Baltimore, MD (2) University of Tennessee Medical Center, Knoxville, TN

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  A Modiri

WE-C930-IePD-F7-5 (Wednesday, 7/13/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: Compared to static field delivery, volumetric-modulated arc therapy reduces high-dose regions in organs at risk (OARs) while accelerating treatment delivery. Current proton therapy solutions employ static fields, which in the setting of multiple gantries result in long treatment times. We explore a novel high-efficiency volumetric-modulated proton arc therapy (HEV-PAT) method that uses a single-energy beam from the cyclotron. The proton beam emerges from a rotating gantry and, after passing through a fixed tertiary energy modulator, deposits its energy inside the target. We hypothesize that irradiating in an arc without requiring an energy change will achieve both clinically desirable dosimetric results and fast delivery.

Methods: We retrospectively analyzed four patient cases: female pelvis, prostate, lung, and brain, with clinical target volumes of 195 cc, 80 cc, 62 cc, and 54 cc, respectively. An arc was simulated out of an original 9–11 static field plan where single-field optimization was performed for each beam and then each beam was converted into sets of 1° gantry-spacing static fields delivering dose to various planar areas within the target. The energy requested from the cyclotron stayed the same for the entire arc and was varied by a modulator at the nozzle.

Results: HEV-PAT plans were comparable to their clinical counterparts in achieving target dose conformity, being robust to uncertainties, and meeting clinical dose-volume constraints. Cyclotron energies were within 159–220 MeV, and modulation was 69–100 MeV, equivalent to 13–19 cm of modulator water-equivalent thickness (WET). Plan delivery times were reduced from >10 min in our clinical practice to <3.5 min in HEV-PAT.

Conclusion: For the evaluated plans, the novel HEV-PAT approach achieved desirable sparing for OARs and shorter delivery times while maintaining target coverage comparable to clinical plans. HEV-PAT’s energy modulator had a WET implementable in a clinical setup.

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