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.
Keywords
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Article info
Publication history
Published online: March 01, 2023
Accepted:
February 18,
2023
Received in revised form:
January 31,
2023
Received:
August 28,
2022
Identification
Copyright
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
