FLASH proton irradiation setup with a modulator wheel for a single mouse eye.

Area of Science:

• Medical Physics
• Radiation Oncology
• Preclinical Research

Background:

• FLASH irradiation, using ultra-high dose rates (>40 Gy/s), may offer similar tumor control to conventional radiotherapy with reduced healthy tissue toxicity.
• Ocular proton radiotherapy is an area of interest for treating eye tumors.
• Verifying the reduced toxicity of FLASH irradiation in the eye is crucial for clinical translation.

Purpose of the Study:

• To present the implemented experimental setup for delivering FLASH proton radiation to the eyes of mice.
• To enable in vivo verification of FLASH irradiation's potential benefits in ocular proton radiotherapy.
• To establish a preclinical model for studying FLASH effects on ocular tissues.

Main Methods:

• Utilized a 68 MeV proton beam from the HZB cyclotron.
• Employed a single scatterer, range shifter, and rotating modulator wheel for beam shaping.
• Used transmission ionization chambers for fast dose monitoring and a beam shutter for precise dose delivery.
• Incorporated a collimating aperture, radioluminescent screen, CCD camera, and Advanced Markus ionization chamber for dosimetry and alignment.
• Radiochromic films (EBT3) were used for supplementary dosimetry and alignment verification.

Main Results:

• Achieved a dose rate of 75 Gy/s, delivering 15 Gy (RBE) within 200 ms with <1% reproducibility.
• Demonstrated a depth-dose distribution with a 5.2 mm range and 0.9 mm distal fall-off.
• Characterized the radiation field with a 6.3 mm diameter PTV, 1.7 mm lateral penumbra, 8% uniformity, and 3% symmetry.

Conclusions:

• The developed setup successfully delivers FLASH proton irradiation to the eyes of anesthetized mice.
• The system allows for rapid switching between conventional and FLASH irradiation modes.
• This setup facilitates further in vivo research into the efficacy and safety of ocular FLASH proton radiotherapy.