Author: Petr Bruza, Rafael Carballeira, Megan Clark, David J. Gladstone, Austin Sloop, Roman Vasyltsiv, Kevin Jacob Willy 👨🔬
Affiliation: Dartmouth College, Thayer School of Engineering, Dartmouth College 🌍
Purpose: Develop an optical dosimetry system to accomplish standard of care on-patient dosimetry and pretreatment quality assurance for ultra-high dose rate (UHDR) electron therapy ahead of human trials of FLASH radiation therapy (FLASH-RT).
Methods: A modified treatment cone was developed to host a dual-camera mount with endoscopic lenses and fit into the treatment head of an Intraop Mobetron linear accelerator (LINAC). Optical dosimetry is employed via imaging at 90Hz, 0.4MP of green-emitting scintillators with two fast CMOS cameras gated to the LINAC pulses for an instantaneous beam’s-eye view of the field of dose for UHDR electrons. Two series of 8 normal and 8 asymmetrical 8 Gy irradiations at 170.9 Gy/s at surface were measured by optical dosimetry and gafchromic film to view flatness and symmetry of the field. Optical density of image frames were summed and compared to the dose captured by film.
Results: The scintillator signal captured with the cameras demonstrates strong agreement to radiochromic film(bias +/- .1%) in the normal field. In addition to spatial dose distributions, the camera enables per-pulse dose monitoring and instantaneous readout, which cannot be accomplished by comparable on-patient dosimetry (film, TLD, or OSLD).
Conclusion: With the use of optical dosimetry, electron FLASH-RT delivery can be monitored at standard of care. This brings the potential to pursue human clinical trials without sacrificing patient safety due to inadequate dosimetry. This system is a first-of-its-kind and demonstrates a streamlined option for pretreatment QA, as well as the option of on-patient scintillating dosimetry with the unique ability to monitor in-vivo dose-per-pulse of UHDR electron therapy. This development enables human clinical trials to be pursued under FDA regulation and guidelines for on-patient dosimetry.