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Purpose: To evaluate the impact of beam quality in terms of distal fall‐off (DFO, 90%–10%) and lateral penumbra (LP, 80%–20%) of single beam ocular proton therapy (OPT) and to derive resulting ideal requirements for future systems. Methods: Nine different beam models with DFO varying between 1 and 4 mm and LP between 1 and 4 mm were created. Beam models were incorporated into the RayStation with RayOcular treatment planning system version 10 B (RaySearch Laboratories, Stockholm, Sweden). Each beam model was applied for eight typical clinical cases, covering different sizes and locations of uveal melanoma. Plans with and without an additional wedge were created, resulting in 117 plans with a total prescribed median dose of 60 Gy(RBE) to the clinical target volume. Treatment plans were analyzed in terms of V20–V80 penumbra volume, D1 (dose to 1% of the volume) for optic disc and macula, optic nerve V30 (volume receiving 30 Gy(RBE), i.e., 50% of prescription), as well as average dose to lens and ciliary body. An LP‐dependent aperture margin was based on estimated uncertainties, ranging from 1.7 to 4.0 mm. Results: V20–V80 showed a strong influence by LP, while DFO was less relevant. The optic disc D1 reached an extra dose of up to 3000 cGy(RBE), comparing the defined technical limit of DFO = LP = 1 mm with DFO = 3 mm/LP = 4 mm. The latter may result from a pencil‐beam scanning (PBS) system with static apertures. Plans employing a wedge showed an improvement for organs at risk sparing. Conclusion: Plan quality is strongly influenced by initial beam parameters. The impact of LP is more pronounced when compared to DFO. The latter becomes important in the treatment of posterior tumors near the macula, optic disc or optic nerve. The plan quality achieved by dedicated OPT nozzles in single‐ or double‐scattering design might not be achievable with modified PBS systems. [ABSTRACT FROM AUTHOR]

Purpose: Recent studies indicate that FLASH irradiation, which involves ultra‐high dose rates in a short time window (usually >40 Gy/s in <500 ms), might be equally efficient against tumors but less harmful to healthy tissues, compared to conventional irradiation with the same total dose. Aiming to verify the latter claim for ocular proton radiotherapy, in vivo experiments with mice are being carried out by Charité – Universitätsmedizin Berlin. This work presents the implemented setup for delivering FLASH proton radiation to a single eye of mice at the Helmholtz‐Zentrum Berlin für Materialien und Energie (HZB). Materials and methods: The HZB cyclotron is tuned to provide a high‐intensity 68 MeV focused proton beam. Outside the vacuum beamline, the protons hit a single scatterer, which also serves as range shifter, and a rotating modulator wheel, which produces a flat depth‐dose distribution. Two transmission ionization chambers in between, read out by fast electronics, are used as dose monitors for triggering an in‐vacuum beam shutter, which blocks the beam once the desired dose has been delivered. A collimating aperture shapes the radiation field at the isocenter, which is measured by a radioluminescent screen and a CCD camera. At the same position, a parallel‐plate ionization chamber of type Advanced Markus® is used for absolute dosimetry and characterization of the spread‐out Bragg peak inside a water phantom. A thin‐foil mirror of adjustable tilt in the beam path assists the correct alignment of the target through side illumination. Radiochromic films of type EBT3 are used to supplement the dosimetry and assist the alignment. Results: A dose rate of 75 Gy/s has been measured, delivering within 200 ms 15 Gy (RBE) with a reproducibility better than ±1%. A depth‐dose curve with a range of 5.2 mm in water, 0.9 mm distal fall‐off (90%–10%), and ±2.5% ripple has been demonstrated, with a PTV of 6.3 mm diameter, 1.7 mm lateral penumbra (90%–10%), 8% uniformity, and 3% symmetry. Conclusions: The implemented setup is able to accommodate ocular irradiation of narcotized mice with protons, targeting selectively the left or the right eye, under conventional and FLASH conditions. Switching between these two modes can be done within half an hour, including the calibration of the dose monitors and the verification of the dose delivery. Further upgrades are planned after the completion of the on‐going experiment. [ABSTRACT FROM AUTHOR]