Comparison of Reconstructed Prompt Gamma Emissions Using Maximum Likelihood Estimation and Origin Ensemble Algorithms for a Compton Camera System Tailored to Proton Range Monitoring

Compton-based prompt gamma (PG) imaging is being investigated by several groups as a potential solution for in vivo range monitoring in proton therapy. The performance of this technique depends on the detector system as well as the ability of the reconstruction method to obtain good spatial resolution to establish a quantitative correlation between the PG emission and the proton beam range in the patient. To evaluate the feasibility of PG imaging for range monitoring, we quantitatively evaluated the emission distributions reconstructed by a Maximum Likelihood Expectation Maximization (MLEM) and a Stochastic Origin Ensemble (SOE) algorithm. To this end, we exploit experimental and Monte Carlo (MC) simulation data acquired with the Polaris-J Compton Camera (CC) prototype. The differences between the proton beam range (

Assessment of the accuracy of an MCNPX-based Monte Carlo simulation model for predicting three-dimensional absorbed dose distributions

In recent years, the Monte Carlo method has been used in a large number of research studies in radiation therapy. For applications such as treatment planning, it is essential to validate the dosimetric accuracy of the Monte Carlo simulations in heterogeneous media. The AAPM Report no 105 addresses issues concerning clinical implementation of Monte Carlo based treatment planning for photon and electron beams, however for proton-therapy planning, such guidance is not yet available. Here we present the results of our validation of the Monte Carlo model of the double scattering system used at our Proton Therapy Center in Houston. In this study, we compared Monte Carlo simulated depth doses and lateral profiles to measured data for a magnitude of beam parameters. We varied simulated proton energies and widths of the spread-out Bragg peaks, and compared them to measurements obtained during the commissioning phase of the Proton Therapy Center in Houston. Of 191 simulated data sets, 189 agreed with measured data sets to within 3% of the maximum dose difference and within 3 mm of the maximum range or penumbra size difference. The two simulated data sets that did not agree with the measured data sets were in the distal falloff of the measured dose distribution, where large dose gradients potentially produce large differences on the basis of minute changes in the beam steering. Hence, the Monte Carlo models of medium- and large-size double scattering proton-therapy nozzles were valid for proton beams in the 100 MeV-250 MeV interval. © 2008 Institute of Physics and Engineering in Medicine

Radiation dosimetry using optically stimulated luminescence in fluoride phosphate optical fibres

Optically stimulated luminescence has been demonstrated within a fluoride phosphate glass optical fibre. These fibres have been used as the basis of a novel dosimeter architecture whereby the optical fibre acts as both the sensing and light guiding component. Fibres were fabricated from a commercially acquired glass and irradiated using a 90Sr/90Y source. Following optical stimulation with a 532 nm laser, optically stimulated luminescence of 483 ± 18 cnts/g/μJ was detected. In addition to OSL, scintillation of 6155 ± 78 cnts/s was also measured. A linear response between 0.16 - 2 Gy of irradiation was measured, after which the intensity was observed to plateau. These results indicate the potential suitability of fluoride phosphate optical fibres for radiation sensing applications.Christopher A. G. Kalnins, Heike Ebendorff-Heidepriem, Nigel A. Spooner and Tanya M. Monr

TH‐C‐T‐617‐02: Effect of Range Modulation On Neutron Dose Equivalent Exposures Around a Passive Scattering Proton Therapy Treatment Nozzle

Purpose: The purpose of our study was to examine the influence of range modulation on the neutron dose equivalent exposures outside the treatment volume around a large‐field passively scattered proton therapy treatment nozzle. Method and Materials: In this study, the neutron dose equivalent spectra per proton (H(E/p)) and total neutron dose equivalent per therapeutic absorbed dose (H/D) were calculated using Monte Carlo simulations of the neutron fluence and the energy dependent neutron fluence‐to‐dose equivalent conversion factor for NCRP 38. (H(E)/p) and H/D were calculated at 54 locations around a passively scattered proton therapy treatment nozzle for varying amounts of range modulation. Results: As the step thickness of the range modulator wheel increased from 1.0 to 12.0 cm, the peak values of H(E)/p increased from 1⋅10−17 to 2⋅10−17 mSv/Gy at 50 cm from isocenter along the beam\u27s central axis. In general, H/D increased with increasing range modulation at all locations studied, and the maximum H/D exposures shifted upstream of isocenter and away from the end of the nozzle. Conclusion: Several important findings can be summarized from the presented work. First, with increasing thickness of the RMW step, the high‐energy peak in the H(E)/p spectra shifted to higher energies. Second, at 90° with respect to the proton beam axis, the high‐energy peak occurs at substantially lower neutron energies. Also, the H/D values around the treatment nozzle increased as the modulation of the beam increased. Finally, the H/D values change significantly with distance from isocenter and angle with respect to the incident beam axis, due in part to the effects of the nozzle components on the neutron fluence downstream of the end of the nozzle. © 2005, American Association of Physicists in Medicine. All rights reserved