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Purpose: X-PACT is an experimental cancer therapy where kV x-rays are used to photo-activate anti-cancer therapeutics through phosphor intermediaries (phosphors that absorb x-rays and re-radiate as UV light). Clinical trials in pet dogs are currently underway (NC State College of Veterinary Medicine) and an essential component is the ability to model the kV dose in these dogs. Here we report the commissioning and characterization of a Monte Carlo (MC) treatment planning simulation tool to calculate X-PACT radiation doses in canine trials. Methods: FLUKA multi-particle MC simulation package was used to simulate a standard X-PACT radiation treatment beam of 80kVp with the Varian OBI x-ray source geometry. The beam quality was verified by comparing measured and simulated attenuation of the beam by various thicknesses of aluminum (2–4.6 mm) under narrow beam conditions (HVL). The beam parameters at commissioning were then corroborated using MC, characterized and verified with empirically collected commissioning data, including: percent depth dose curves (PDD), back-scatter factors (BSF), collimator scatter factor(s), and heel effect, etc. All simulations were conducted for N=30M histories at M=100 iterations. Results: HVL and PDD simulation data agreed with an average percent error of 2.42%±0.33 and 6.03%±1.58, respectively. The mean square error (MSE) values for HVL and PDD (0.07% and 0.50%) were low, as expected; however, longer simulations are required to validate convergence to the expected values. Qualitatively, pre- and post-filtration source spectra matched well with 80kVp references generated via SPEKTR software. Further validation of commissioning data simulation is underway in preparation for first-time 3D dose calculations with canine CBCT data. Conclusion: We have prepared a Monte Carlo simulation capable of accurate dose calculation for use with ongoing X-PACT canine clinical trials. Preliminary results show good agreement with measured data and hold promise for accurate quantification of dose for this novel psoralen X-ray therapy. Funding Support, Disclosures, & Conflict of Interest: The Monte Carlo simulation work was not funded; Drs. Adamson & Oldham have received funding from Immunolight LLC for X-PACT research.

Purpose: Accurate dosimetry is essential when irradiating mice to ensure that functional and molecular endpoints are well understood for the radiation dose delivered. Conventional methods of prescribing dose in mice involve the use of a single dose rate measurement and assume a uniform average dose throughout all organs of the entire mouse. Here, the authors report the individual average organ dose values for the irradiation of a 12, 23, and 33 g mouse on a 320 kVp x-ray irradiator and calculate the resulting error from using conventional dose prescription methods. Methods: Organ doses were simulated in the Geant4 application for tomographic emission toolkit using the MOBY mouse whole-body phantom. Dosimetry was performed for three beams utilizing filters A (1.65 mm Al), B (2.0 mm Al), and C (0.1 mm Cu + 2.5 mm Al), respectively. In addition, simulated x-ray spectra were validated with physical half-value layer measurements. Results: Average doses in soft-tissue organs were found to vary by as much as 23%–32% depending on the filter. Compared to filters A and B, filter C provided the hardest beam and had the lowest variation in soft-tissue average organ doses across all mouse sizes, with a difference of 23% for the median mouse size of 23 g. Conclusions: This work suggests a new dose prescription method in small animal dosimetry: it presents a departure from the conventional approach of assigning a single dose value for irradiation of mice to a more comprehensive approach of characterizing individual organ doses to minimize the error and uncertainty. In human radiation therapy, clinical treatment planning establishes the target dose as well as the dose distribution, however, this has generally not been done in small animal research. These results suggest that organ dose errors will be minimized by calibrating the dose rates for all filters, and using different dose rates for different organs.

We developed a mouse dosimetry model for neutron beam, and compared the calculated and simulated neutron doses for a water target (mouse) exposed to a 10 MeV neutron beam. We also estimated the longitudinal neutron dose profile for the water target. A water bottle (a simulated mouse, 6 cm × 1.3 cm radius) was exposed to a flux of 10 MeV neutrons produced via the d( d, n)He reaction using the Tandem accelerator at Triangle Universities Nuclear Laboratory at Duke University. An estimation of the neutron flux was obtained by neutron activations of two sets of aluminum and gold activation foils. One foil of each type was placed at the front and back sides of the water target. The flux was then calculated based on gamma spectroscopy of the irradiated foils using HPGe detectors. A Monte Carlo(MC) simulation based on FLUKA2008 code , was also used to estimate the 10 MeV neutron dose for the same geometry. The highest neutron flux measured using the activation technique was (8.538×106 +/− 6.89×104) n.cm−2.s−1 at the front end of the target. Using neutron kerma factors from ICRU data tables, the calculated dose rate to a water target at the location of the foil was (1.890+/− 0.015) Gy.hr−1. Using the data from the MC simulation, the calculated neutron dose to the front end of the water target was (1.870 +/− 0.001) Gy.hr−1. The dose calculated using the foil activation technique was in good agreement with the MC results. The slight discrepancy in the measured flux was likely the result of the closer position of the activation foils to the neutron source than the water bottle target, and also absorption within the activation foils. Assuming these results are in good agreement, we estimated the dose profile for the simulated mouse.

The purpose of this paper is to estimate neutron doses using radiochromic XRQA films. Five radiochromic films, placed at varying distances from the neutron source and a water bottle, were exposed to a flux of 10 MeV neutrons produced via the d(d, n)He reaction using the Tandem accelerator at Triangle Universities Nuclear Laboratory at Duke University. An estimation of the neutron flux was obtained by neutron activations of two sets of aluminum and gold activation foils. One foil of each type was placed at the front and back sides of the water target. The flux calculation was based on gamma spectroscopy of the irradiated foils using HPGe detectors. A Monte Carlo(MC) simulation based on FLUKA2008 code was also used to estimate the 10 MeV neutron dose for the same geometry. The accuracy of the results from MC was verified by the comparison of dose on water target from MC with the dose calculated on the same target using flux and the ICRU data tables. Based on these results, a calibration curve was obtained for optical density of the film vs. absorbed neutron dose in the range of 0–20 Gy. We have demonstrated the potential application of radiochromic films for neutrondosimetry. This research was, in part, supported by National Institute of Allergy and Infectious Diseases Grant 5U19 AI067798‐03