Treatment of ocular tumors through a novel applicator on a conventional proton pencil beam scanning beamline

Abstract

Treatment of ocular tumors on dedicated scattering-based proton therapy systems is standard afforded due to sharp lateral and distal penumbras. However, most newer proton therapy centers provide pencil beam scanning treatments. In this paper, we present a pencil beam scanning (PBS)-based ocular treatment solution. The design, commissioning, and validation of an applicator mount for a conventional PBS snout to allow for ocular treatments are given. In contrast to scattering techniques, PBS-based ocular therapy allows for inverse planning, providing planners with additional flexibility to shape the radiation field, potentially sparing healthy tissues. PBS enables the use of commercial Monte Carlo algorithms resulting in accurate dose calculations in the presence of heterogeneities and fiducials. The validation consisted of small field dosimetry measurements of point doses, depth doses, and lateral profiles relevant to ocular therapy. A comparison of beam properties achieved through the applicator against published literature is presented. We successfully showed the feasibility of PBS-based ocular treatments.

Design and characterization of an aperture system and spot configuration for ocular treatments with a gantry‐based spot scanning proton beam

“…Recently, Regmi et al reported lateral penumbras at 1 mm depth ranging from 2.6-3.6 mm with their spot scanning system. 11 While a strict comparison is difficult since these parameters are dependent on factors such as target size and depth, the results obtained using the aperture developed in this work are firmly within these ranges.In a spot scanning system the distal penumbra is dominated by the highest energy layer used. As seen in Figure 3a, the highest energy expected to be used with this system is 121.0 MeV, which has a D80 of 61 mm and a 90%−10% distal fall-off of 2.4 mm.…”

“…The aperture system developed in this work was designed to treat ocular sites on a gantry-based spot scanning proton beam. While at least two institutions have previously reported the ability to treat ocular sites with a non-dedicated eyeline, 10,11 the majority of centers are treating ocular sites in fixed beam rooms with a dedicated eyeline. The aperture system presented here demonstrates the possibility of treating ocular sites on an existing clinical spot scanning proton gantry.…”

“…used a transversal spot spacing of 2 mm, 10 while Regmi et al. used a clinical treatment planning system to optimize spot placement 11 . The approach used in this work was chosen to minimize the number of spots to improve delivery efficiency, reduce leakage, reduce the lateral penumbra, and minimize the size of the aperture to improve compatibility with a gaze monitoring system.…”

“…10 In addition, a center in Seattle has developed a brass aperture mount to treat ocular sites with their universal pencil beam scanning beamline. 11 In order to improve the accessibility of proton therapy to ocular melanoma patients,continued work on using spot scanning proton beams to achieve the beam characteristics required to treat ocular sites is necessary. This allows ocular patients to be treated in the same setting as other patients receiving proton therapy and results in expanded access.…”

“…Since the OPTIC survey, an Italian center has used a raster scanning proton beam with a fixed horizontal beam line to treat ocular sites using a brass aperture 10 . In addition, a center in Seattle has developed a brass aperture mount to treat ocular sites with their universal pencil beam scanning beamline 11 . In order to improve the accessibility of proton therapy to ocular melanoma patients, continued work on using spot scanning proton beams to achieve the beam characteristics required to treat ocular sites is necessary.…”