Dosimetric accuracy of an HDR brachytherapy treatment planning system for different irradiation lengths with monte carlo simulation

OBJECTIVE The purpose of the present study was to verify calculated dose rate profiles of Ir-192 for four different irradiation lengths and various numbers of dwell positions by using treatment planning system (TPS) calculations and Monte Carlo (MC) simulations. METHODS Dose rate profiles per air-kerma strength in μGy m ² /h (abbreviated as U) were calculated on transverse axis for irradiation lengths of 2, 3, 4, and 5 cm by Nucletron Oncentra TPS. The same irradiation scenarios were simulated with Monte Carlo N-Particle (MCNP) Transport Code. The MC and TPS calculated dose rate profiles were compared for all settings. RESULTS The difference between the calculated dose rate profiles by MC and TPS was found within 2% at an interval of 2 mm–8 cm away from the source for all irradiation lengths. The largest discrepancy of 5.2% was computed at a distance of 10 cm from the source for 5 cm irradiation length. CONCLUSION There is a good consistency between the calculated dose rate profiles by MCNP and Oncentra TPS. The deviation between the calculated dose rate values slightly increases as the distance from the source center increases >5 cm from the source, and its quantity depends on the number of dwell positions.