KEY POINTS
- This clinical proof-of-concept study evaluated 4 fractions in 1 patient receiving proton therapy for recurrent inoperable pancreatic cancer, integrating prompt-gamma measurements, beam delivery logs, breathing signals, and control computed tomography.
- The treatment delivered 66 Gy relative biological effectiveness in 30 fractions to the high-risk clinical target volume and 51 Gy relative biological effectiveness to the low-risk volume, with respiratory motion suppressed to less than 3 mm.
- Control computed tomography–based simulations and prompt-gamma measurements showed median range shifts below 2.3 mm, supporting the technical feasibility of the four-dimensional verification workflow.
- Planning computed tomography–based evaluation showed small deviations during fractions 11 and 15, with absolute median shifts of 2.1 mm or less, but larger shifts of approximately 6 mm during fractions 23 and 25.
- The later range overshoot of 4–6 mm corresponded to a 5-kg weight loss and visible surface changes. Target coverage and organ-at-risk doses nevertheless remained clinically acceptable.
CLINICAL TAKEAWAY
Motion-aware prompt-gamma imaging may provide independent in vivo proton range verification for abdominal and other moving targets while detecting clinically relevant anatomical change without additional imaging dose. This remains an early technical proof of concept from one patient treated with breathing suppression, and larger studies under more varied motion conditions are required before routine clinical implementation.