Program Information
The Effect of Inter-Seed Attenuation and Tissue Composition in Prostate 125I Brachytherapy Dose Calculations
K Tamura1*, F Araki2 , T Ohno2 , (1) Kumamoto University, Kumamoto, Kumamoto, (2) Kumamoto University, Kumamoto, Kumamoto,
Presentations
SU-F-T-46 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
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 x 1 x 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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