Mahbubur Rahman1, Petr Bruza2, Katja M Langen3, David J Gladstone4, Xu Cao2, Brian W Pogue2, Rongxiao Zhang5. 1. Thayer School of Engineering at Dartmouth, 14 Engineering Drive, Hanover, Hanover, New Hampshire, 03755-8001, UNITED STATES. 2. Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, UNITED STATES. 3. Radiation Oncology, Emory University, Atlanta, Georgia, UNITED STATES. 4. Thayer School of Engineering , Dartmouth College, Hanover, New Hampshire, UNITED STATES. 5. Dartmouth College Geisel School of Medicine, Hanover, New Hampshire, UNITED STATES.
Abstract
PURPOSE: The goal of this work was to create a technique that could measure all possible spatial and temporal delivery rates used in pencil-beam scanning (PBS) proton therapy. The proposed system used a fast scintillation screen for full-field imaging to resolve temporal and spatial patterns as it was delivered. METHODS AND MATERIALS: A fast intensified CMOS camera imaged used continuous mode 10 ms temporal frame rate and 1x1 mm^2 spatial resolution, imaging a scintillation screen during clinical proton PBS delivery. PBS plans with varying dose, dose rate, energy, field size, and spot-spacing were generated, delivered and imaged. The captured images were post processed to provide dose and dose rate values after background subtraction, perspective transformation, uniformity correction for the camera and the scintillation screen, and calibration into dose. RESULTS: The linearity in scintillation response with respect to varying dose rate, dose, and field size was within 2%. The quenching corrected response with varying energy was also within 2%. Large spatio-temporal variations in dose rate were observed, even for plans delivered with similar dose distributions. Dose and dose rate histograms and maximum dose rate maps were generated for quantitative evaluations. With the fastest PBS delivery on a clinical system, dose rates up to 26.0 Gy/s were resolved. CONCLUSIONS: The scintillation imaging technique was able to quantify proton PBS dose rate profiles with spot weight as low as 2 MU, with spot-spacing of 2.5 mm, having an ultimate 1x1 mm^2 spatial resolution. These dose rate temporal profiles, spatial maps, and cumulative dose rate histograms provide useful metrics for the potential evaluation and optimization of dose rate in treatment plans.
PURPOSE: The goal of this work was to create a technique that could measure all possible spatial and temporal delivery rates used in pencil-beam scanning (PBS) proton therapy. The proposed system used a fast scintillation screen for full-field imaging to resolve temporal and spatial patterns as it was delivered. METHODS AND MATERIALS: A fast intensified CMOS camera imaged used continuous mode 10 ms temporal frame rate and 1x1 mm^2 spatial resolution, imaging a scintillation screen during clinical proton PBS delivery. PBS plans with varying dose, dose rate, energy, field size, and spot-spacing were generated, delivered and imaged. The captured images were post processed to provide dose and dose rate values after background subtraction, perspective transformation, uniformity correction for the camera and the scintillation screen, and calibration into dose. RESULTS: The linearity in scintillation response with respect to varying dose rate, dose, and field size was within 2%. The quenching corrected response with varying energy was also within 2%. Large spatio-temporal variations in dose rate were observed, even for plans delivered with similar dose distributions. Dose and dose rate histograms and maximum dose rate maps were generated for quantitative evaluations. With the fastest PBS delivery on a clinical system, dose rates up to 26.0 Gy/s were resolved. CONCLUSIONS: The scintillation imaging technique was able to quantify proton PBS dose rate profiles with spot weight as low as 2 MU, with spot-spacing of 2.5 mm, having an ultimate 1x1 mm^2 spatial resolution. These dose rate temporal profiles, spatial maps, and cumulative dose rate histograms provide useful metrics for the potential evaluation and optimization of dose rate in treatment plans.