Monte Carlo dosimetry for a new 32P brachytherapy source using FLUKA code

Purpose
Dosimetric characterization of a new 32P brachytherapy source was studied and the validity of the FLUKA code to reproduce the dosimetric parameters in a water phantom was evaluated. In addition, dose rate distributions around the 32P source sheathed by a catheter and unsheathed source were investigated in different tissue phantoms.

Material and methods
The new 32P source was modeled using FLUKA Monte Carlo code. According to the AAPM TG-60 recommendations, reference of absorbed dose rate, radial dose function, anisotropy function, and an away-along table for quality assurance purposes inside water phantom were calculated. Moreover, the results of the radial dose function and dose rate were obtained for the sheathed source and unsheathed sources at radial distances in different tissue phantoms: liver, fat tissue, 9-component soft tissue, and 4-component soft tissue.

Results
The calculated dosimetric parameters of the new 32P source by FLUKA code in water phantom agreed well with that of the GEANT4 calculation. The 2D away-along dose results were similar to the GEANT4 simulation for distances less than 0.25 cm, small differences were apparent at long distances from the source. Dose rate evaluation for the sheathed source shows that the presence of a catheter increases the dose values up to 2.11% in comparison with the unsheathed source in water phantom. Our results show that the radial dose function calculated in water, as generalized by AAPM TG-60, differed in tissue, especially at large distances from the source.

Conclusions
This work fully characterizes dosimetric parameters of the sheathed and unsheathed new 32P brachytherapy sources in water and different tissue phantoms by using FLUKA code. The results demonstrate that the dose distribution in water differed from the calculated ones in tissue phantoms due to the densities and atomic composition for tissues that are not taken account by the TG-60 formalism.