Development and application of in-vivo dose and time-resolved measurements for clinical application of ultra-high dose rate radiotherapy

Background and purpose: Ultra-high-dose-rate (UHDR) radiotherapy (RT) has emerged as a promising technique to widen the therapeutic window. However, clinical implementation is critically dependent on standardized dosimetry systems. This study reports on the integration of passive and active detectors for in-vivo dose monitoring in a clinical setting. Materials and methods: Four detector systems were evaluated for patient treatments with UHDR at a modified C-arm linear accelerator (linac) (9 MeV, dose per pulse 1.08 Gy, average dose rate 216 Gy/s): two passive systems − optically stimulated luminescence detectors (OSLDs) and radiochromic films − and two active systems − a scintillator and a diamond detector. The detectors were positioned on a dedicated 3D-printed mount or the patient’s skin to measure integral dose and time-resolved parameters. OSLDs were calibrated against a reference ion chamber and validated under varying conditions. Scintillator and diamond detectors recorded pulse-to-pulse and intra-pulse stability, respectively. Results: OSLDs provided reproducible dose reporting within ±5%, with precision improved through averaging multiple chips. The pulse-to-pulse stability measured with the scintillator was in agreement with the diamond detector measurements within ±1%. The diamond detector resolved intra-pulse stability and identified instabilities in case of poor beam tuning. Conclusions: The combined use of OSLDs, scintillator, diamond, and film detectors enabled robust and time-resolved recording of UHDR RT in a clinical trial setting. While resource-intensive, this approach ensured redundancy and precision, providing a feasible strategy for early clinical adoption.