Volumetric scintillation dosimetry for scanned proton beams

Scanned beam proton therapy is a promising cancer treatment modality which is becoming more widely available with the increasing number of proton radiotherapy centers. Scanned proton beams can produce complex 3D dose distributions, presenting a challenge for adequate quality assurance testing. Because each scanned beam dose measurement requires the delivery of the entire field, multiple measurements can be time consuming. These quality assurance challenges limit the number of patients who can be treated with this modality. The overall objective of this project is to increase the safety and availability of complex proton therapy treatments by developing a fast volumetric scintillation detector. Volumetric scintillation dosimetry is a new technique with the potential to provide fast, high-resolution measurements of scanned proton beams. Initial studies using scintillation dosimetry for IMPT quality assurance have shown promise, despite quenching effects caused by the nonlinear response of the scintillator to low-energy protons. All previous studies have used a single camera to image a tank of scintillator. However, to obtain real-time 3D information, at least two cameras are required. The purpose of this study is to develop a dual-camera volumetric scintillation dosimetry system and test its capabilities for quality assurance of scanned proton beams. A prototype detector was built, consisting of a tank of LS imaged by two orthogonally-positioned CCD cameras. The optical response of the system was evaluated, and correction methods were developed for optical artifacts. Quenching correction methods were developed to preserve the linearity of dose measurement in the Bragg peak. The new detector was used to measure the range, lateral profile, and lateral position of scanned proton beams of multiple energies and lateral locations. A high level of accuracy was obtained with the range and lateral profile measurements. The lateral position measurements were precise but suffered from systematic errors related to uncertainties in the day-to-day setup of the detector. The new detector design shows the potential to significantly improve the efficiency and comprehensiveness of quality assurance measurements for scanned proton beam delivery systems. It provides the novel capability of measuring the proton beam range, lateral profile, and lateral position simultaneously and rapidly with high resolution. These capabilities will facilitate increased patient safety and an improved capacity to detect beam delivery errors