BACKGROUND
Despite spinal metastases accounting for 10% to 30% of new tumors diagnoses annually, and radiation therapy is a standard treatment technique, the studies discussing the effects of small-size spinal prostheses on spinal radiation therapy are limited.
OBJECTIVE
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.
METHODS
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.
CONCLUSIONS
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.
A Monte Carlo approach to lung dose calculation in small fields used in intensity modulated radiation therapy and stereotactic body radiation therapy
