Monte Carlo and experimental high dose rate ¹⁹²Ir brachytherapy dosimetry with microDiamond detectors

The purpose of this study was to investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW-Freiburg, Germany) for radial dose function measurements with High Dose Rate (HDR) ¹⁹²Ir brachytherapy sources. An HDR ¹⁹²Ir source model mHDR v2r (Nucletron BV, an Elekta company, The Netherlands) was placed at the centre of a MP3 water phantom (PTW-Freiburg, Germany) within a 4F needle. Three mDDs were employed to measure the radial dose function of the source by acquiring profiles along the source transverse axis. Meanwhile, the experimental setup was simulated using the Monte Carlo (MC) code MCNP6.1™ (Los Alamos National Laboratory, USA) to calculate phantom-size, absorbed-dose energy dependence and volume averaging correction factors. After applying the correction factors, the radial dose function g_L(r) for the line source approximation was calculated as defined in the TG-43 formalism at radial distances from 0.5cm to 10cm and compared to the consensus g_L(r) (ESTRO and AAPM). The percentage differences to the consensus g_L(r) for all the three mDDs were from -2.3% to +1.4% for distances r≤5cm and -6.2% to +2.6% for larger distances. These results indicate the suitability of the mDD for HDR brachytherapy measurements when all required corrections are applied.