Exhibit Hall | Forum 4
Purpose: To assess suitability of the 3D PRESAGE phantom for relative dose measurements in a high dose per pulse FLASH electron beam.
Methods: Irradiations were performed using a Varian 2100 C/D linear accelerator, converted to deliver ultrahigh-dose-rate 10 MeV electron beam. The LINAC delivered approximately 0.7 Gy/pulse for FLASH irradiations. Dose rate was varied from about 40 Gy/s to 240 Gy/s by changing the repetition rate. PRESAGE phantoms were irradiated en face at six FLASH dose rates: 40 Gy/s, 80 Gy/s, 120 Gy/s, 160 Gy/s, 200 Gy/s, and 240 Gy/s. For each irradiation, film and scintillator measurements were used to verify dose. The dose to the phantom was then evaluated using a novel broad-beam optical CT scanner with a fiber optic taper for collimated imaging. Optical density measurements were converted to dose using percent depth dose curves calculated by Monte Carlo.
Results: At depths past D90, optical density as a function of depth for six FLASH dose rates (240-40 Gy/s) are nearly identical, indicating the phantom to be dose rate independent. At depths near to and shallower than Dmax there was increased uncertainty in the results due to unevenness in the phantom surface and edge effects in the optical CT scan.
Conclusion: PRESAGE 3D phantoms show dose rate independence for a wide range of ultrahigh-dose-rate electron beams, indicating these phantoms may be useful for relative dose measurements in FLASH electron beams. Further improvements should be made to minimize uncertainties observed at shallow depths and to investigate PRESAGE for absolute dosimetry in FLASH.
3D, Radiation Dosimetry, Electron Therapy
TH- Radiation Dose Measurement Devices: 3D solid gel/plastic