Dosimetry in the vicinity of a 192Ir brachytherapy line source in air

Dose calculation in brachytherapy is based on the assumption that the radiation sources defining a matrix of dwell positions are point-like. The planning systems, however, do not sufficiently take into account the finite extension of the sources. The present study focused on the problem of dosimetry in the vicinity of a 192Ir brachytherapy line source, particularly for small source-target distances (< 1 cm). Distance-dependent dose measurements were performed using a diamond detector with high spatial resolution. The measured distributions were then compared with dose calculations based on the extended version of the Sievert's integral for line sources. The first approach utilizes the classical Sievert's formulation. The second approach takes into account the finite extension of the detector surface, resulting in improved agreement with the measured dose distribution. Finally, the effect of self-attenuation within the source is also included. This further reduces the deviation between dose calculations and measurements. (orig.)