SU-F-T-46: The Effect of Inter-Seed Attenuation and Tissue Composition in Prostate 125I Brachytherapy Dose Calculations

Authors


Abstract

Purpose:

To investigate the difference of dose distributions with/without the effect of inter-seed attenuation and tissue compositions in prostate 125I brachytherapy dose calculations, using Monte Carlo simulations of Particle and Heavy Ion Transport code System (PHITS).

Methods:

The dose distributions in 125I prostate brachytherapy were calculated using PHITS for non-simultaneous and simultaneous alignments of STM1251 sources in water or prostate phantom for six patients. The PHITS input file was created from DICOM-RT file which includes source coordinates and structures for clinical target volume (CTV) and organs at risk (OARs) of urethra and rectum, using in-house Matlab software. Photon and electron cutoff energies were set to 1 keV and 100 MeV, respectively. The dose distributions were calculated with the kerma approximation and the voxel size of 1 × 1 × 1 mm3. The number of incident photon was set to be the statistical uncertainty (1σ) of less than 1%. The effect of inter-seed attenuation and prostate tissue compositions was evaluated from dose volume histograms (DVHs) for each structure, by comparing to results of the AAPM TG-43 dose calculation (without the effect of inter-seed attenuation and prostate tissue compositions).

Results:

The dose reduction due to the inter-seed attenuation by source capsules was approximately 2% for CTV and OARs compared to those of TG-43. In additions, by considering prostate tissue composition, the D90 and V100 of CTV reduced by 6% and 1%, respectively.

Conclusion:

It needs to consider the dose reduction due to the inter-seed attenuation and tissue composition in prostate 125I brachytherapy dose calculations.

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