Range verification by prompt gamma-ray imaging and timing: Activities at OncoRay

The promise of particle therapy at ultimate precision can only be fulfilled once the particle range can be controlled and verified with millimeter precision. In spite of considerable efforts made by research groups and commercial enterprises throughout the world, means or devices for routinely measuring the particle range in situ and in real time during treatments are still missing. On the one hand, prompt gamma-ray imaging (proposed almost 15 years ago) has become widely accepted as the most promising strategy for online range verification. On the other hand, none of the Compton camera concepts pursued by several groups (including our group at HZDR/OncoRay) could prove to be applicable under treatment conditions. The only prototype system ever used in a clinical trial is the passively collimated knife-edge slit camera by IBA. This “camera” cannot provide 3D images, but measures one-dimensional prompt gamma-ray intensity profiles that allow quantifying possible shifts of the distal edge of high-weighted single pencil beam spots. Alternative, potentially less expensive approaches have been proposed by MGH (prompt gamma spectroscopy) and OncoRay (prompt gamma timing). Efforts to translate these ideas in applicable technologies are underway.
The talk will review the state-of-the art in prompt-gamma based range verification, with a focus on contributions of OncoRay: (1) the development and exploration of the prompt gamma-ray timing technique, and (2) the preparation and execution of first-in-man prompt gamma-ray imaging with the IBA knife-edge slit camera.