Radiotherapy dose calculations in high-Z materials: comprehensive comparison between experiment, Monte Carlo, and conventional planning algorithms.

PURPOSE To compare the accuracies of the AAA and AcurosXB dose calculation algorithms and to predict the change in the down-stream and lateral dose deposition of high energy photons in the presence of material with densities higher that commonly found in the body. METHOD Metal rods of titanium (d =4.5g/m2), stainless steel (d=8g/cm2) and tungsten (d=19.25 g/cm2) were positioned in a phantom. Film was position behind and laterally to the rods to measure the dose distribution for a 6 MV, 18 MV and 10 FFF photon beams. A DOSXYZnrc Monte Carlo simulation of the experimental setup was performed The AAA and AcurosXB dose calculation algorithms were used to predict the dose distributions. The dose from film and DOSXYZnrc were compared with the dose predicted by AAA and AcurosXB. RESULTS AAA overestimated the dose behind the rods by 15-25% and underestimated the dose laterally to the rods by 5-15% depending on the range of materials and energies investigated. AcurosXB overestimated the dose behind the rods by 1-18% and underestimated the dose laterally to the rods by up to 5% depending on the range of material and energies investigated. CONCLUSION AAA cannot deliver clinically acceptable dose calculation results at a distance less than 10 mm from metals, for a single field treatment. Acuros XB is able to handle metals of low atomic numbers (Z ≤ 26), but not tungsten (Z = 74). This can be due to the restriction of the CT-density table in EclipseTM TPS, which has an upper HU limit of 10501.