Room: ePoster Forums
Purpose: Recent studies using ultra-high-dose-rate (â€œFLASHâ€?; 40-100 Gy/s) electron radiotherapy point to a reduced radiotoxicity in lung, brain, and intestine. The purpose of this work was to develop methods for preclinical testing of proton FLASH radiotherapy.
Methods: A clinical proton facility was used to deliver scanned-beam proton irradiations to mouse lung at conventional and FLASH dose rates, to examine differences in radiotoxicity. Prior to animal irradiations, dosimetric testing was carried out using a plane-parallel ionization chamber (PPIC), a Faraday Cup dosimeter, and radiochromic films. An acrylic platform was constructed to allow x-ray imaging, positioning with uncertainty of Â±2 mm, and proton irradiation for 10 mice at once.
Results: Dosimetric comparison between the PPIC and the Faraday Cup revealed agreement in measurement in the range of nozzle proton currents from 0.65 nA to 80 nA at 245 MeV. The primary beam monitor did not agree with the PPIC or Faraday Cup at proton currents higher than 16 nA, leading up to a 400% difference in beam output at 80 nA, requiring correction. For a scanned 245-MeV proton rectangular lung field, a proton current of 52 nA at the nozzle corresponded to a FLASH dose rate of 40 Gy/s. We used 0.65 nA, corresponding to 0.5 Gy/s, as our conventional dose-rate control. Measured lung doses were 15.2 Â± 0.2 Gy and 14.9 Â± 0.2 Gy for conventional and FLASH irradiations, respectively. Regarding timing, the irradiation of 10 mice with 15 Gy required 300 s and 3.75 s, respectively.
Conclusion: Our experimental platform allowed for efficient use of proton beamtime, precise animal positioning, and corrected for the non-linear response of the beam control system seen at FLASH dose rates. Proton FLASH therapy might be quickly translated to human trials, likely requiring relatively minor modification of the primary beam monitor and nozzle electronics.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by a Research Grant from Varian Medical Systems (Palo Alto, CA).