Development of a Technique to Simultaneously Verify Linear Energy Transfer and Absorbed Dose in Therapeutic Proton Beams

The biological response resulting from proton radiotherapy depends on both the absorbed dose in the irradiated tissue and the linear energy transfer (LET) of the beam. Currently, the optimization of proton therapy treatment plans is based only on absorbed dose. However, recent advances in proton therapy delivery have made it possible to vary the LET distribution for a potential therapeutic gain. As a result, researchers and clinicians have investigated the use of LET as an additional parameter in proton therapy treatment optimization. To safely deliver such treatment plans, it would be ideal to have a method in place to measure and verify both absorbed dose and LET as part of a quality assurance program. While absorbed dose is readily measured using a variety of detectors, there is no device available for the routine measurement and verification of LET.In this thesis, optically stimulated luminescence (OSL) techniques are investigated for simultaneous measurements of absorbed dose and LET. A Monte Carlo infrastructure to simulate LET distributions in a proton therapy beamline is first developed. Using the simulated LET values, the LET dependence of OSL detectors is thoroughly characterized. Two parameters of the OSL signal, representing the OSL curve shape and the ratio of UV to blue emission intensities, are used to generate LET calibration curves. These curves facilitate the measurement of LET using OSL detectors. Additionally, a new OSL technique is developed to measure absorbed dose in therapeutic proton beams of varying LET.The potential of the OSL techniques is demonstrated by using them to measure LET and absorbed dose under new irradiation conditions, including real patient-specific proton therapy treatment plans. In the beams investigated, OSL techniques are found to measure dose-weighted LET within 7.9% of the MC simulated values, and absorbed dose within 2.5% of ionization chamber measurements.