Proton Therapy for Uveal Melanoma on a Pencil Beam Scanning Gantry

We present our experience treating ocular tumors in a standard pencil beam scanning (PBS) gantry room without apertures, which could broaden access to proton therapy for patients with ocular cancer globally. Besides, this study explores the dosimetric benefits of beam-specific apertures.

We retrospectively evaluated 11 consecutive patients with uveal melanoma treated in a clinic gantry room. The dose deviations between the planned and received by the patient were investigated by assessing the forward calculation of the treatment plan on the synthetic computed tomography of cone beam computed tomography. Each plan was forward calculated with a beam-specific brass aperture (BSA) using a Monte Carlo algorithm to explore dosimetric improvements. We compared the plan quality to the delivered plan (DP) using target coverage (D95%) and mean/maximum doses to the adjacent organs.

A close agreement between the planned and delivered dose was achieved, with D95% deviations within 3.6% for all treatments, maintaining dose constraints for critical organs. Similar target coverage was reached, with D95% at 101% ± 1.0% (DP) and 101% ± 3.2% (BSA). BSA was effective (P < .05) in reducing the mean [D _Mean (DP, BSA)Gy] and maximum [D _Max (DP, BSA)Gy] dose to organs: retina D _Mean (37.7, 29.5), cornea D _Mean (10.7, 2.4), conjunctiva D _Mean (13.6, 4.1), lacrimal gland D _Mean (25.5, 14.1), optic nerve D _Mean (19.6, 13.1), lens D _Max (22.4, 8.5), cornea D _Max (24.4, 10.2), eyebrow D _Max (15.3, 6.8). BSA lowered the mean dose to surrounding organs and significantly decreased the maximum dose to nonabutting organs (lens, cornea, eyebrow), but had little impact on the maximum dose to the abutting organs (retina, optic nerve).

We demonstrate the successful implementation of ocular proton treatment with a standard PBS gantry beamline without apertures. The beam-specific apertures effectively reduced doses to the organs adjacent to the target in the PBS proton treatment while maintaining similar target coverage. This approach offers an opportunity to expand access to ocular proton therapy widely.