Dosimetric investigation of high dose rate Ir-192 source with Monte Carlo method

Background: This study aims to calculate the air-kerma strength (SK), the dose rate constant (∧) and the dose rate profiles of a Gammamed 12i Ir-192 source by using the Monte Carlo technique and to compare the dose rate values with those calculated by the Abacus HDR treatment planning system (TPS). Materials and Methods: Air-kerma strength (in units of U; 1 U= μGy m2 h-1) and the dose rate constant (∧) of a Gammamed 12i Ir-192 source were computed with the Monte Carlo-based code MCNP. For a single dwell position, profiles of dose rate per air kerma rate strength (in unit of U) along the x axis were obtained with MCNP and compared with data from the Abacus TPS at y=0, 1, and 2 cm. Results: The air-kerma strength and the dose rate constant of the source were calculated to 9.98×10-8 U and 1.106 cGy h-1 U-1, respectively. The maximum dose differences between MCNP and TPS along the x axis were found to be 1.3, 3.7 and 5.4% at distances more than 1 cm away from the source center for y= 0, 1 and 2 cm planes, respectively. Conclusion: The dose rate profiles calculated with MCNP and by the TPS show good agreement except for points located beyond the tip of the source.