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Location: Marriott Marquis
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PQA 02 - PQA 02 Physics Poster Q&A

2296 - Enhancing Organs-at-Risk Protection in Ocular SBRT with Bragg-Peak FLASH Biological Optimization

Sunday, September 29, 2024
4:45 PM – 6:00 PM ET
Location: Hall C

Screen: 11

M. Hamza1, B. Selvaraj2, G. Lattery1, C. Cheng3, X. Zhao2, T. Kaulfers1, A. Zhai2, F. Yu2, Z. Han2, I. J. Choi2,4, C. B. Simone II2,4, C. A. Barker4, J. Chang1,5, M. Kang2, and H. Lin2,4; 1Physics and Astronomy, Hofstra University, Hempstead, NY, 2New York Proton Center, New York, NY, 3Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, 4Memorial Sloan Kettering Cancer Center, New York, NY, 5Northwell, New Hyde Park, NY

Purpose/Objective(s): The treatment of ocular cancers presents a significant challenge: delivering sufficient doses to tumors while preserving the functions of the nearby critical organs-at-risk (OARs). This study investigates the efficacy of proton pencil beam scanning (PBS) combined with Bragg-peak FLASH (BP-FLASH) biological optimization (FBO) in ocular treatment. We hypothesize that BP-FLASH FBO can increase treatment dose while enhancing OAR protection. Materials/

Methods: The BP-FLASH technique can provide similar tumor control as conventional PBS(CONV) treatment with additional normal-tissue sparing due to FLASH effect. However, the FLASH sparing effect has not been incorporated into the treatment planning system for plan optimization. In this study, FLASH-sparing factors for various normal tissues around the eyes were derived from literature to model the FLASH-sparing effect and incorporated into the FBO module of an in-house treatment planning system (TPS). Ten consecutive ocular patients previously treated with CONV-SBRT to 50Gy in 5 fractions were included in this study. Each case was replanned using the single-energy BP-FLASH technique with non-aperture PBS. Dose metrics of the CONV-SBRT and BP-FLASH plans were compared, including the CTV coverage, and the mean and maximal dose to surrounding OARs: cornea, eye, optic nerves, retina, lacrimal gland, and conjunctiva. Dose escalation was also performed by increasing the prescription dose to 60Gy in 5 fractions for the BP-FLASH plans, and the plan quality was then evaluated to assess if all clinical constraints were met.
Results: All plans for both techniques met the clinical objectives for all OARs, although the clinical CONV-SBRT plans slightly outperformed the BP-FLASH plan for the regimen of 50Gy in 5 fractions. When planning using the FBO method, the maximum doses to the cornea, eye, optic nerves, retina, lacrimal gland, and conjunctiva of BP-FLASH plans were, on average 11.2%, 15.8%, 30.1%, 20.1%, 14.4% and 17.6% lower, respectively, than those of CONV-SBRT plans. In comparison to the CONV-SBRT 50Gy plans, the BP-FLASH 60Gy plan using FBO had achieved reduced maximum doses to the eye, optic nerves, retina, lacrimal gland, and conjunctiva by a mean of 16.1%, 28.9%, 22.3%, 15.0%, and 18.7%, respectively.
Conclusion: BP-FLASH is capable of producing treatment plans comparable in quality to those of CONV-PBS for the existing 10 Gy x 5 SBRT protocol. Through FBO, BP-FLASH can increase the dose to 60 Gy in 5 fractions, without an expected increase in toxicity relative to CONV-SBRT treatments using 50Gy, demonstrating BP-FLASH’s potential to reduce ORA doses for ocular treatment significantly.