Improved lateral penumbra for proton ocular treatments on a general-purpose spot scanning beamline. (March 2023)

• Record Type: Journal Article
• Authors: Saini, Jatinder; Maes, Dominic; Regmi, Rajesh; Fung, Angela; Bloch, Charles; Schwarz, Marco; Stacey, Andrew; Chen, Jonathan; Rengan, Ramesh; Halasz, Lia
• Is Part Of: Physica medica. Volume 107(2023)
• Publication Date: 2023-03
• Subjects: Ocular proton therapy -- Pencil beam scanning -- General-purpose beamline -- Lateral penumbra; Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2023.102551
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Our solution converts a commercial IBA high energy scanning beamline to allow for ocular proton therapy. Abstract: Purpose: An ocular applicator that fits a commercial proton snout with an upstream range shifter to allow for treatments with sharp lateral penumbra is described. Materials and Methods: The validation of the ocular applicator consisted of a comparison of range, depth doses (Bragg peaks and spread out Bragg peaks), point doses, and 2-D lateral profiles. Measurements were made for three field sizes, 1.5, 2, and 3 cm, resulting in 15 beams. Distal and lateral penumbras were simulated in the treatment planning system for seven range-modulation combinations for beams typical of ocular treatments and a field size of 1.5 cm, and penumbra values were compared to published literature. Results: All the range errors were within 0.5 mm. The maximum averaged local dose differences for Bragg peaks and SOBPs were 2.6% and 1.1%, respectively. All the 30 measured point doses were within +/-3% of the calculated. The measured lateral profiles, analyzed through gamma index analysis and compared to the simulated, had pass rates greater than 96% for all the planes. The lateral penumbra increased linearly with depth, from 1.4 mm at 1 cm depth to 2.5 mm at 4 cm depth. The distal penumbra ranged from 3.6 to 4.4 mm and increased linearly with the range. The treatment time for a single 10 Gy (RBE) fractional dose ranged from 30 to 120 s, depending on the shape and size of the target. Conclusions: The ocular applicator's modified design allows lateral penumbra similar to dedicated ocular beamlines while enabling planners to use modern treatment tools such as Monte Carlo and full CT-based planning with increased flexibility in beam placement.