Sep 30

SS 34 - Radiation and Cancer Physics 5: In Vivo Dosimetry and Treatment Verification

296 - Recovering Dose Dynamics and Dose Rate Volume Histograms in UHDR PBS Proton Therapy Using Scintillation Array Dosimetry

08:20am - 08:30am PT

Room 307/308

Presenter(s)

Roman Vasyltsiv, BS - Dartmouth College, Hanover, NH

R. Vasyltsiv¹, J. Harms², M. Clark³, Y. Zhang⁴, Z. Xiao⁵, R. Zhang⁶, B. W. Pogue⁷, D. J. Gladstone⁸, A. E. Mascia⁹, and P. Bruza³; ¹Dartmouth College, Hanover, NH, ²Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, AL, ³Thayer School of Engineering, Dartmouth College, Hanover, NH, ⁴Department of Radiation Oncology, University of Cincinnati Medical Center, Cincinnati, OH, ⁵Cincinnati Children's Hospital, Cincinnati, OH, ⁶Department of Radiation Oncology, University of Missouri, Columbia, MO, ⁷DoseOptics, LLC, Lebanon, NH, ⁸Department of Medicine, Geisel School of Medicine, Dartmouth College, Hanover, NH, ⁹Varian, Milpitas, OH

Purpose/Objective(s):

Rapid integration of ultra-high dose rate (UHDR) pencil beam scanning proton therapy in FLASH clinical trials has created a need for advanced treatment verification tools. Current in vivo dosimetry systems are unable to provide the spatiotemporal resolution required to monitor and validate UHDR treatments, often being limited to 1D measurements or lacking sufficient temporal capability. Given that full field dose rate verification is of utmost importance in FLASH clinical trials, we developed a novel wide-area scintillation imaging system geared for surface-based monitoring of UHDR proton therapy in a clinical FLASH setting. This system is designed to monitor 2D surface dose and dose rate maps in patient coordinates with intra-pulse temporal resolution and integrate the surface measurements with the planning CT data to generate 3D dose and dose rate volume histograms (DVH/DRVH) directly from treatment data.

Materials/Methods:

We developed a high speed dosimetry system using a 2500 FPS intensified CMOS camera, stereovision positioning, and a 11×21 cm² deformable scintillator array. Array impact on beam structure was verified via water equivalent thickness at 160/220 MeV. Following irradiation, the scintillation images were geometrically corrected and translated to dose. To emulate the full clinical workflow the array was attached to the rib region of an anthropomorphic phantom, CT-imaged, and irradiated using a mock UHDR PBS plan (99 nA, 250 MeV). Dynamic surface dose measurements were registered to the CT and analytically projected through the volume to generate 3D DVH and DRVH for the lung, rib, and surrounding tissues. Dose and dose rate metrics derived from scintillation imaging were compared to log values to validate system performance. Setup time and material activation were investigated.

Results:

The array WET was measured as 1.1 mm for both energies, and post-irradiation surveys showed negligible material activation at 671 nSv/hr. A total of ~1 min of setup was added to the workflow for array positioning. The system demonstrated <0.5mm spatial and 0.4ms temporal resolution, resolving continuous dose gradients up to 8Gy/cm and local PBS dose rate variation exceeding 15000 Gy/s/cm. Analysis of the depth projected DVH showed agreement at isocenter (8.21 +/- 0.13Gy) with log-derived dose (8.1Gy). DRVH derived from scintillation imaging showed high agreement with <1% deviation in volume coverage at 48Gy/s.

Conclusion:

The scintillation imaging system presented in this work provides high resolution spatial and temporal monitoring of surface dose and dose rate for FLASH proton therapy with minimal impact on clinical workflow. Its ability to monitor surface dose dynamics and generate dose and dose rate volume histograms directly from treatment data presents a significant advancement for in vivo dosimetry, preparing it for translation to clinical trials.