Modeling and understanding the doses around the neutron generator provides insightful data in regard to radiation safety and protection precautions. Published data can be used to predict doses, but realistic data for the Nuclear Engineering Teaching Laboratory’s Thermo MP 320 Neutron Generator helps health physicists more accurately predict dose rates and protect experimenters against exposure. The goal was to create a model inclusive of the entire setup and room where the neutron generator is housed. Monte Carlo N-Particle (MCNP) Code reigns as the preferred method for modeling radiation transport and was utilized to model the transport of neutrons within the current configuration of the 14 MeV neutron generator facility. This model took into account all shielding materials and their respective dimensions and locations within the concrete room. By utilizing tallies and tally modifiers, the model predicts dose rates that can be used with experimental factors such as irradiation time and flux to predict a dose in millirem. Validation experiments were performed in the current setup using Landauer Luxel®+ with Neutrak dosimeters placed in strategic locations to record the neutron dose vi received as well as a Ludlum Model 42-41 PRESCILA neutron probe to predict dose rates. The dosimeters and PRESCILA measurement locations matched the positions of the point detector tallies in MCNP. After laboratory analysis, a comparison was performed between the model output and the dosimeter and PRESCILA values to successfully validate the accuracy of the model. / text

Acuros External Beam (Acuros XB) is a new radiation dose calculation algorithm available as part of Varian Medical Systems' radiotherapy treatment planning system, ECLIPSE. Acuros XB calculates dose distributions by finding the deterministic solution to the linear Boltzmann transport equation which governs the transport of particles or radiation through matter. Among other things, Acuros XB claims an ability to accurately model dose perturbations due to increased photon and electron scatter within a high-density volume, such as a hip prosthesis. Until now, the only way to accurately model high-density scatter was with a Monte Carlo simulation which gives the stochastic solution to the same transport equation, but is time and computationally expensive. In contrast, Acuros XB solves the transport equation at time scales appropriate for clinical use. An evaluation of Acuros XB for radiation dose calculations involving high-density objects was undertaken using EGSnrc based Monte Carlo as the benchmark. Calculations were performed for geometrically ideal virtual phantoms, water tank phantoms containing cylindrical steel rods and hip prostheses, and for a clinical prostate treatment plan involving a unilateral prosthetic hip. The anisotropic analytical algorithm (AAA), a convolution-superposition algorithm used for treatment planning at the British Columbia Cancer Agency's Vancouver Island Center, was also used to illustrate the limitations of current radiotherapy planning tools. In addition, to verify the qualitative properties of dose perturbations due to high-density volumes, film measurements were taken and compared to Monte Carlo, Acuros XB and AAA data. Dose distributions calculated with Acuros XB agree very well with distributions calculated with Monte Carlo. Gamma-analyses performed at 2% and 2 mm using Monte Carlo as the reference dose were within tolerance for 92-99% of voxels considered. AAA, on the other hand, was within tolerance for 61-97% of voxels considered under the same gamma-constraints. For the clinical prostate plan, AAA produced localized dose underestimates that were absent when calculated by Acuros XB. As well, both Monte Carlo and Acuros XB showed very good agreement with the film measurements, while AAA showed large discrepancies at and beyond the location of measured dose perturbations. Acuros XB has been shown to handle does perturbations due to high-density volumes as well as Monte Carlo, at clinically appropriate time scales, and better than the current algorithm used for treatment planning at the Vancouver Island Center. / Graduate