Megavolt Bremsstrahlung Measurements from Linear Induction Accelerators Demonstrate Possible Use as a FLASH Radiotherapy Source to Reduce Acute Toxicity

Abstract

Recent studies indicate better efficacy and healthy tissue sparing with high dose-rate FLASH radiotherapy (FLASH-RT) cancer treatment. This technique delivers a prompt high radiation dose rather than fractional doses over a longer period of time. The threshold is >40 Gy-s-1 with a maximal effect at >100 Gy-s-1 that must be maintained in the treatment volume. Mechanisms are still widely debated, but toxicity is minimized while inducing apoptosis in malignant tissue. Delivery technologies to date show that a capability gap exists with clinic scale, broad area, deep penetrating, high dose rate capability. Based on present trends, if FLASH-RT is adopted, it may become a dominant approach except in the least technologically advanced countries. The linear induction accelerator (LIA) developed for high current, high repetition rate, species independent charged particle acceleration, has yet to be considered for this application. We briefly review the status of LIA technology, explore the physics of bremsstrahlung-converter-target interactions and our work on stabilizing the electron beam. While the gradient of the LIA is low, we present our preliminary work to improve the gradient by an order of magnitude, presenting a point design for a multibeam FLASH-RT system using a single accelerator for application to conformal FLASH-RT.