Gas-to-wall absorbed dose conversion factors for neutron energies of 25 to 250 MeV

Cavity chamber absorbed dose measurements do not usually strictly adhere to the conditions of the Fano theorem and therefore the differences in the gas and wall mass stopping powers must be taken into account. Values of gas-to-wall absorbed dose conversion factors rm,g were calculated for neutron energies of 25 to 250 MeV for detectors with walls of C, O, Mg, Al, Si, Fe, Zr, AlN, Al2O3, SiO2, ZrO2, and A-150 tissue-equivalent (TE) plastic and with gas cavities of acetylene, dry air, Ar, an Ar-CO2 mixture, CO2, isobutane, isobutane-based TE, methane, methane-based TE, propane, and propane-based TE. The rm,g calculations required initial spectral fluences of 1H, 2H, 3H, 3He, and 4He ions released by neutron reactions in the walls, and these were calculated with the Los Alamos High Energy Transport code. Mass-stopping-power data were taken from Ziegler and co-workers. Additional calculations were made in order to test the sensitivity of rm,g to input data from other sources, i.e., ion spectral fluences from the ALICE nuclear reaction code and mass-stopping powers from the recent ICRU evaluation. © 1997 Academic Press

Intercomparision of Monte Carlo radiation transport codes MCNPX, GEANT4, and FLUKA for simulating proton radiotherapy of the eye

Monte Carlo simulations of an ocular treatment beam- line consisting of a nozzle and a water phantom were carried out using MCNPX, GEANT4, and FLUKA to compare the dosimetric accuracy and the simulation efficiency of the codes. Simulated central axis percent depth- dose profiles and cross-field dose profiles were compared with experimentally measured data for the comparison. Simulation speed was evaluated by comparing the number of proton histories simulated per second using each code. The results indicate that all the Monte Carlo transport codes calculate sufficiently accurate proton dose distributions in the eye and that the FLUKA transport code has the highest simulation efficiency

The predicted relative risk of premature ovarian failure for three radiotherapy modalities in a girl receiving craniospinal irradiation

In girls and young women, irradiation of the ovaries can reduce the number of viable ovarian primordial follicles, which may lead to premature ovarian failure (POF) and subsequently to sterility. One strategy to minimize this late effect is to reduce the radiation dose to the ovaries. A primary means of reducing dose is to choose a radiotherapy technique that avoids irradiating nearby normal tissue; however, the relative risk of POF (RRPOF) due to the various therapeutic options has not been assessed. This study compared the predicted RRPOF after craniospinal proton radiotherapy, conventional photon radiotherapy (CRT) and intensity-modulated photon radiotherapy (IMRT). We calculated the equivalent dose delivered to the ovaries of an 11-year-old girl from therapeutic and stray radiation. We then predicted the percentage of ovarian primordial follicles killed by radiation and used this as a measure of the RRPOF; we also calculated the ratio of the relative risk of POF (RRRPOF) among the three radiotherapies. Proton radiotherapy had a lower RRPOF than either of the other two types. We also tested the sensitivity of the RRRPOF between photon and proton therapies to the anatomic position of the ovaries, i.e., proximity to the treatment field (2 ≤ RRRPOF ≤ 10). We found that CRT and IMRT have higher risks of POF than passive-scattering proton radiotherapy (PRT) does, regardless of uncertainties in the ovarian location. Overall, PRT represents a lower RRPOF over the two other modalities. © 2013 Institute of Physics and Engineering in Medicine

Neutron Interferometry Using a Single Modulated Phase Grating

Neutron grating interferometry provides information on phase and small-angle scatter in addition to attenuation. Previously, phase grating moir\'e interferometers (PGMI) with two- or three-phase gratings have been developed. These phase-grating systems use the moir\'e far-field technique to avoid the need for high-aspect absorption gratings used in Talbot-Lau interferometers (TLI) which reduce the neutron flux reaching the detector. We first demonstrate through theory and simulations a novel phase grating interferometer system for cold neutrons that requires a single modulated phase grating (MPG) for phase-contrast imaging, as opposed to the two- or three-phase gratings in previously employed PGMI systems. The MPG theory was compared to the full Sommerfeld-Rayleigh Diffraction integral simulator. Then we compared the MPG system to experiments in the literature that use a two-phase-grating-based PGMI with best-case visibility of around 39%. An MPG with a modulation period of 300 micron, pitch of 2 micron, and grating heights with a phase modulation of (pi,0), illuminated by a monochromatic beam, produces a visibility of 94.2% with comparable source-to-detector distance (SDD) as the two-phase-grating-based PGMI. Phase sensitivity, another important performance metric of the grating interferometer, was compared to values available in the literature, viz. the conventional TLI with phase sensitivity of 4.5 x 10E+3 for an SDD of 3.5 m and a beam wavelength of 0.44 nm. For a range of modulation periods, the MPG system provides comparable or greater theoretical maximum phase sensitivity of 4.1 x 10E+3 to 10.0 x 10E+3 for SDDs of up to 3.5 m. This proposed MPG system can provide high-performance PGMI that obviates the need to align two phase gratings.Comment: Manuscript accepted in Rev. Sci. Instrum. vol. 94, 045110, (2023), (Published Online: 17 April 2023

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

A scintillator‐based approach to monitor secondary neutron production during proton therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135048/1/mp3813.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135048/2/mp3813_am.pd

A GPU implementation of a track-repeating algorithm for proton radiotherapy dose calculations

An essential component in proton radiotherapy is the algorithm to calculate the radiation dose to be delivered to the patient. The most common dose algorithms are fast but they are approximate analytical approaches. However their level of accuracy is not always satisfactory, especially for heterogeneous anatomic areas, like the thorax. Monte Carlo techniques provide superior accuracy, however, they often require large computation resources, which render them impractical for routine clinical use. Track-repeating algorithms, for example the Fast Dose Calculator, have shown promise for achieving the accuracy of Monte Carlo simulations for proton radiotherapy dose calculations in a fraction of the computation time. We report on the implementation of the Fast Dose Calculator for proton radiotherapy on a card equipped with graphics processor units (GPU) rather than a central processing unit architecture. This implementation reproduces the full Monte Carlo and CPU-based track-repeating dose calculations within 2%, while achieving a statistical uncertainty of 2% in less than one minute utilizing one single GPU card, which should allow real-time accurate dose calculations