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.

Spatial response of synthetic microDiamond and diode detectors measured with kilovoltage synchrotron radiation

PURPOSE

To map the spatial response of four solid-state radiation detectors of types commonly used for radiotherapy dosimetry.

METHODS

PTW model 60016 Diode P, 60017 Diode E, 60018 Diode SRS, and 60019 microDiamond detectors were radiographed using a high resolution conventional X-ray system. Their spatial response was then investigated using a 0.1 mm diameter beam of 95 keV average energy photons generated by a synchrotron. The detectors were scanned through the beam while their signal was recorded as a function of position, to map the response. These 2D response maps were created in both the end-on and side-on orientations.

RESULTS

The results show the location and size of the active region. End-on, the active area was determined to be centrally located and within 0.2 mm of the manufacturer's specified diameter. The active areas of the 60016 Diode P, 60017 Diode E, 60018 Diode SRS detectors are uniform to within approximately 5%. The 60019 microDiamond showed local variations up to 30%. The extra-cameral signal in the microDiamond was calculated from the side-on scan to be approximately 8% of the signal from the active element.

CONCLUSIONS

The spatial response of four solid-state detectors has been measured. The technique yielded information about the location and uniformity of the active area, and the extra-cameral signal, for the beam quality used.