Evaluation of dosimetric parameters for various 192Ir brachytherapy sources under unbounded phantom geometry by Monte Carlo simulation.

As per TG-43 dose calculation formalism, it is essential to obtain various dosimetric parameters such as the air-kerma strength, dose rate constant, radial dose function, and anisotropy function, as they account for accurate determination of dose rate distribution around brachytherapy sources. Most of the available reported Monte Carlo simulations were performed in liquid water phantoms with a bounded region of 30-cm diameter. In this context, an attempt was made to report the dosimetric parameters for various commercially available pulsed-dose rate (PDR) and high-dose rate (HDR) sources under unbounded phantom conditions, as the data may be used as input to treatment planning systems (TPSs) for quality control assistance. The air-kerma strength per unit activity, S(k)/A, was computed for various Iridium-192 ((192)Ir) sources in dry air medium. The air-kerma strength and dose rate constant for old PDR is (9.77 +/- 0.03) 10(-8) U/Bq and 1.124 +/- 0.001 cGyh(-1)U(-1); for new PDR, the values are (9.96 +/- 0.03) 10(-8) U/Bq and 1.124 +/- 0.001 cGyh(-1)U(-1); for old MHDR, the values are (9.80 +/- 0.01) 10(-8) U/Bq and 1.115 +/- 0.001 cGyh(-1)U(-1); for new MHDR, (9.80 +/- 0.01) 10(-8) U/Bq and 1.112 +/- 0.001cGyh(-1)U(-1); for old VHDR, the values are (10.32 +/- 0.01) 10(-8) U/Bq and 1.035 +/- 0.002 cGyh(-1)U(-1); for new VHDR, the values are (10.34 +/- 0.02) 10(-8) U/Bq and 1.096 +/- 0.001 cGyh(-1)U(-1). The computed radial dose function values and anisotropy function values are also in good agreement with available data.