Purpose: Radiation-induced lung injury is a dose limiting factor in thoracic radiotherapy. Ultra-high dose rate (FLASH) radiation holds promises for augmenting the therapeutic window for thoracic cancers. This study aimed to develop a platform for murine whole thoracic lung irradiation with electron FLASH radiotherapy at variable dose rates.
Methods: A FLASH-enabled Varian linear accelerator was used to provide the FLASH and conventional (CONV) electron beams at 16 MeV. A Cerrobend collimator with a 1.6 cm wide slit was created to collimate the electron beam, and was supported by a QFix Tilt-ProTM Tiling Base (QFix, Avondale, PA) attached to the treatment couch. Control of the FLASH dose rate and dose was realized by adjusting the couch vertical position and the number of monitor units (MUs), respectively. Achievable doses and dose rates were investigated at 1 cm depth in solid water phantoms, using the Gafchromic™ EBT-XD films (Ashland Inc, Bridgewater, NJ, USA). Percent depth dose (PDD) and dose profiles at variable FLASH and CONV dose rates were also measured at depths from 0 to 2 cm.
Results: This platform supported FLASH dose rates from 19 to 100 Gy.s⁻¹ following an inverse-square relationship with the distance from the virtual source. A linear relationship between dose and the number of MUs was established. Similar PDDs and dose profiles were observed under the CONV and FLASH modes. Scattering of electrons along the beam path widened the beam penumbra, with the 90% field width ranging from 1.5 cm at 0 cm depth to 1.1 cm at 1.5 cm depth.
Conclusion: Preliminary film dosimetry revealed the achievable FLASH dose rates and doses of the proposed platform, and demonstrated comparable dose distribution at CONV and FLASH modes. Thus, this platform offers a useful tool for investigation of the FLASH effect in murine lungs.
Not Applicable / None Entered.