Time-resolved diode dosimetry calibration through Monte Carlo modeling for in vivo passive scattered proton therapy range verification.

PURPOSE: Our group previously introduced an in vivo proton range verification methodology in which a silicon diode array system is used to correlate the dose rate profile per range modulation wheel cycle of the detector signal to the water-equivalent path length (WEPL) for passively scattered proton beam delivery. The implementation of this system requires a set of calibration data to establish a beam-specific response to WEPL fit for the selected 'scout' beam (a 1 cm overshoot of the predicted detector depth with a dose of 4 cGy) in water-equivalent plastic. This necessitates a separate set of measurements for every 'scout' beam that may be appropriate to the clinical case. The current study demonstrates the use of Monte Carlo simulations for calibration of the time-resolved diode dosimetry technique. METHODS: Measurements for three 'scout' beams were compared against simulated detector response with Monte Carlo methods using the Tool for Particle Simulation (TOPAS). The 'scout' beams were then applied in the simulation environment to simulated water-equivalent plastic, a CT of water-equivalent plastic, and a patient CT data set to assess uncertainty. RESULTS: Simulated detector response in water-equivalent plastic was validated against measurements for 'scout' spread out Bragg peaks of range 10 cm, 15 cm, and 21 cm (168 MeV, 177 MeV, and 210 MeV) to within 3.4 mm for all beams, and to within 1 mm in the region where the detector is expected to lie. CONCLUSION: Feasibility has been shown for performing the calibration of the detector response for three 'scout' beams through simulation for the time-resolved diode dosimetry technique in passive scattered proton delivery.

Late radiation toxicity in Hodgkin lymphoma patients: proton therapy's potential.

In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity-modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six-month consecutive period of 2010 were retrieved. Twenty-six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p > 0.05, p > 0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p < 0.001, p < 0.001) and breast cancers (p< 0.001, p< 0.001) as compared to 3D CRT.

Treatment of ocular tumors through a novel applicator on a conventional proton pencil beam scanning beamline.

Treatment of ocular tumors on dedicated scattering-based proton therapy systems is standard afforded due to sharp lateral and distal penumbras. However, most newer proton therapy centers provide pencil beam scanning treatments. In this paper, we present a pencil beam scanning (PBS)-based ocular treatment solution. The design, commissioning, and validation of an applicator mount for a conventional PBS snout to allow for ocular treatments are given. In contrast to scattering techniques, PBS-based ocular therapy allows for inverse planning, providing planners with additional flexibility to shape the radiation field, potentially sparing healthy tissues. PBS enables the use of commercial Monte Carlo algorithms resulting in accurate dose calculations in the presence of heterogeneities and fiducials. The validation consisted of small field dosimetry measurements of point doses, depth doses, and lateral profiles relevant to ocular therapy. A comparison of beam properties achieved through the applicator against published literature is presented. We successfully showed the feasibility of PBS-based ocular treatments.