Verification of dose calculation accuracy of RTP systems by Monte Carlo simulation

High dose rate brachytherapy has attained the good local control for cervix cancer because radioactive source can be put close to tumors, resulting in increasing the dose delivery per one fraction. However, quality assurance must be accompanied to reduce severe complication. We verified the dose distribution around the source by comparing measured dose with calculated dose by Radiation Therapy Planning systems (RTPS) as well as Monte Carlo simulation. We found as much as 10-30 % differences around Ir-192 source between measured dose with TLD (BeO)/grass dosimeters and calculated dose. The differences of the calculation algorithm of dose distribution affect about 10% between PLATO and Buchler facts. The source structure considerably affects the dose distribution especially in the forward direction. These data suggest that the appropriate parameters such as anisotropy function, radial dose function etc must be verified by their calculation algorism and source structures in the clinical practice of quality assurance. (author)