Background and Aims

We present the rigorous commissioning of a modified LINAC to deliver ultrahigh dose-rate (UHDR) electron beam and implementation of its model in a widely adopted treatment planning system (TPS) with minimal changes to the clinical setting.

Methods

A Varian Clinac 2100C/D was converted to deliver UHDR beams by withdrawing the target and scattering foil in 10MV x-ray mode. Beam characteristics and stability were quantified by film, Cherenkov, and scintillation imaging. The Geant4 generated beam model was validated with film and implemented in Varian Eclipse TPS. Electron FLASH radiotherapy (eFLASH-RT) plans were generated for representative mammal and human patient cases accounting for complex geometries and anatomical inhomogeneities.

Results

The surface mean-dose-rate at the isocenter was >230Gy/s for all measured fields with adequate long-term stability (deviations of output <7%, symmetry/flatness <2%, spatial shift and FWHM <2mm). The TPS model was validated to clinical accuracy (average error <1.5% for lateral profiles and <2% for percent-depth-dose profiles). Treatments plans were generated and accurately delivered to normal porcine skin surface tissue and a melanoma tumor in a canine’s posterior oral cavity. A human eFLASH-RT plan comparable to a conventional electron plan was achieved by utilizing routine accessories, oblique gantry angle and couch kick.

Conclusions

Treatment planning and accurate delivery of eFLASH-RT were feasible in minimally modified radiation oncology clinical settings. The modifications and open-source TPS model are readily transferable to facilitate clinical translation of eFLASH-RT.

Acknowledgment: This work was supported by the Norris Cotton Cancer Center (grant P30CA023108) and Thayer School of Engineering (seed funding and grant R01EB024498).