Monte Carlo study of the relationship between skin dose and optically stimulated luminescence dosimeter dose in Pd-103 permanent breast seed implant brachytherapy.

PURPOSE

To establish a method for estimating skin dose for patients with permanent breast seed implant based on in vivo optically stimulated luminescence dosimeters (OSLDs) measurements.

METHODS AND MATERIALS

Monte Carlo simulations were performed in a simple breast phantom using the EGSnrc user code egs_brachy. Realistic models of the IsoAid Advantage Pd-103 brachytherapy source and Landauer nanoDot OSLD were created to model in vivo skin dose measurements where an OSLD would be placed on the skin of a patient with permanent breast seed implant following implantation. Doses to a 0.2 cm volume of skin beneath the OSLD and to the sensitive volume within the OSLD were calculated, and the ratio of these values was found for various seed positions inside the breast phantom. The maximum value of this ratio may be used as a conversion factor that would allow skin dose to be estimated from in vivo OSLD measurements.

RESULTS

Conversion factors of 0.5 and 1.44 are recommended for OSLDs calibrated to dose to AlO and water, respectively, at the point of measurement in the OSLD. These factors were not significantly affected by the addition of extra seeds in the dose calculations.

CONCLUSIONS

A method for estimating skin dose from OSLD measurements was proposed. Individual institutions should calibrate OSLDs to Pd-103 seeds to apply the results of this work clinically.