Dose calculations in heterogeneous volumes with the GATE Monte Carlo software for radiological protection

Abstract

Monte Carlo methods have become widespread in the field of radiation protection and in particular in medical physics where the use of voxelized volumes for the reconstruction of dosimetric quantities is increasing. Changing the resolution of a dose map can be useful to compare dosimetric results coming from voxelized volumes with different resolutions, or to reduce computation time. This can be done by superimposing a dosel grid with a different resolution than that of the voxelized volume. In this case, each dosel will cover several voxels, leading the Monte Carlo code to calculate the dose in heterogeneous volumes. Two algorithms are available in GATE to perform these calculations, the Volume-Weighting (V-W) and the Mass-Weighting (M-W) algorithms, the latter being the subject of this work. In a general way, the M-W algorithm tends to reconstruct a higher dose than that the V-W one. In dosels involving heavy and lightweight materials (air-skin, bone-tissue), the M-W reconstructed dose is better estimated than the V-W one (up to 10% better at the air-skin interface). Moreover, the statistical uncertainty of the M-W dose can be up to 80% lower than the V-W one at air-skin interfaces. These results show that the M-W algorithm is more suitable for radiological protection applications and must be preferentially used in GATE for dose calculations in heterogeneous volumes.

The GATE-RTion/IDEAL Independent Dose Calculation System for Light Ion Beam Therapy

“…: cut, step size) can be set-up as a compromise between speed and accuracy [5]. The dose scoring is handled by the so-called DoseActor attached to the cropped CT image, using the mass weighting algorithm, which is the most accurate method available in GATE for scoring the dose [25]. Depending on the settings, the dose to medium or the dose to water are scored using the resolution of the CT [26].…”

Technical note: A fast and accurate analytical dose calculation algorithm for 125I seed‐loaded stent applications

“…The digital voxelized phantoms were constructed from the postimplantation CTs using GATE 27 according to a correlation between HU value and mass density as well as elemental weights. The default volume weighting algorithm was adopted, which means that the dose inside a dose grid was computed as the sum of the absorbed dose of the volume voxels contained in that dose grid weighted by their respective volume fractions 28 . As the CT value of the seed is relatively high, the positions of the seeds were first automatically located in CT images.…”

“…The default volume weighting algorithm was adopted, which means that the dose inside a dose grid was computed as the sum of the absorbed dose of the volume voxels contained in that dose grid weighted by their respective volume fractions. 28 As the CT value of the seed is relatively high, the positions of the seeds were first automatically located in CT images. Then the position and orientation of the stent were determined from the location of the seeds.…”