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Technical note| Volume 107, 102551, March 2023

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Improved lateral penumbra for proton ocular treatments on a general-purpose spot scanning beamline

  • Jatinder Saini
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Dominic Maes
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Rajesh Regmi
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Angela Fung
    Affiliations
    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Charles Bloch
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Marco Schwarz
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Andrew Stacey
    Affiliations
    Department of Ophthalmology, University of Washington School of Medicine, 750 Republican St, Seattle, WA 98109, USA
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  • Jonathan Chen
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Ramesh Rengan
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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  • Lia Halasz
    Affiliations
    Department of Radiation Oncology, University of Washington School of Medicine, 1959 NE Pacific St., Seattle, WA 98195, USA

    Fred Hutchinson Cancer Center, 1570 N 115th St., Seattle, WA 98133, USA
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Published:March 01, 2023DOI:https://doi.org/10.1016/j.ejmp.2023.102551

      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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