The effect of rib and lung heterogeneities on the computed dose to lung in Ir-192 high-dose-rate breast brachytherapy: Monte Carlo versus a treatment planning system

A Monte Carlo study on dose distribution evaluation of Flexisource (192)Ir brachytherapy source

AIM

The aim of this study is to evaluate the dose distribution of the Flexisource (192)Ir source.

BACKGROUND

Dosimetric evaluation of brachytherapy sources is recommended by task group number 43 (TG. 43) of American Association of Physicists in Medicine (AAPM).

MATERIALS AND METHODS

MCNPX code was used to simulate Flexisource (192)Ir source. Dose rate constant and radial dose function were obtained for water and soft tissue phantoms and compared with previous data on this source. Furthermore, dose rate along the transverse axis was obtained by simulation of the Flexisource and a point source and the obtained data were compared with those from Flexiplan treatment planning system (TPS).

RESULTS

The values of dose rate constant obtained for water and soft tissue phantoms were equal to 1.108 and 1.106, respectively. The values of the radial dose function are listed in the form of tabulated data. The values of dose rate (cGy/s) obtained are shown in the form of tabulated data and figures. The maximum difference between TPS and Monte Carlo (MC) dose rate values was 11% in a water phantom at 6.0 cm from the source.

CONCLUSION

Based on dosimetric parameter comparisons with values previously published, the accuracy of our simulation of Flexisource (192)Ir was verified. The results of dose rate constant and radial dose function in water and soft tissue phantoms were the same for Flexisource and point sources. For Flexisource (192)Ir source, the results of TPS calculations in a water phantom were in agreement with the simulations within the calculation uncertainties. Furthermore, the results from the TPS calculation for Flexisource and MC calculation for a point source were practically equal within the calculation uncertainties.