Background and purpose Prompt-gamma imaging (PGI) can detect deviations between planned and delivered proton spots. To date, prompt-gamma imaging has been limited to body sites not influenced by regular motion or substantial intrafraction anatomical changes that can affect the proton range during treatment delivery. This study investigates the feasibility of time-resolved (4D) prompt-gamma imaging treatment verification with a PGI slit camera, incorporating breathing motion in a first patient application. Material and methods Synchronously acquired beam delivery (log files), breathing phase and prompt-gamma imaging data are evaluated in 3D and 4D for four fractions with control CTs of a pancreatic cancer patient. Results The first 4D PGI workflow was developed. The median range shifts between control CT-based simulation and PGI measurements were < 2.3 mm. Planning-CT-based interfraction PGI evaluations showed good agreement between planned and delivered spots for early fractions (median shift <2.1 mm), but larger deviations (median shift ~6 mm) for later fractions, related to progressive patient weight loss visible on the control CTs. Differences between 3D and 4D PGI were small, due to breathing suppression applied as part of the standard clinical protocol. Conclusions A 4D PGI workflow has been successfully developed and tested on a pancreatic-cancer patient, suggesting the feasibility of PGI-based treatment verification for patients with tumors affected by respiratory motion, even though the proof-of-concept measurements were done with breathing suppression.
Berthold et al. (Mon,) studied this question.
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