Dosimetry and characterization of a 25 MeV proton beam line for pre-clinical radiobiology research.

Purpose With the increase in proton therapy centers, there is a growing need to make progress in preclinical proton radiation biology to give accessible data to medical physicists and practicing radiation oncologists. Methods A cyclotron usually producing radioisotopes with a proton beam at an energy of about 25 MeV after acceleration, was used for radiobiology studies. Depleted silicon surface barrier detectors were used for the beam energy measurement. A complementary metal oxide semiconductor (CMOS) sensor and a plastic scintillator detector were used for fluence measurement, and compared to Geant4 and an in-house analytical dose modeling developed for this purpose. Also, from the energy measurement of each attenuated beam, the dose-averaged linear energy transfer (LETd) was calculated with Geant4. Results The measured proton beam energy was 24.85 +/- 0.14 MeV with an energy straggling of 127 +/- 22 keV before scattering and extraction in air. The measured flatness was within +/- 2.1% over 9 mm in diameter. A wide range of LETd is achievable: constant between the entrance and the exit of the cancer cell sample ranging from 2.2 to 8 keV/mu m, beyond 20 keV/mu m, and an average of 2-5 keV/mu m in a scattering spread-out Bragg peak calculated for an example of a 6-mm-thick xenograft tumor. Conclusion The dosimetry and the characterization of a 25-MeV proton beam line for preclinical radiobiology research was performed by measurements and modeling, demonstrating the feasibility of delivering a proton beam for preclinical in vivo and in vitro studies with LETd of clinical interest.