Application of the PTW microDiamond in small field dosimetry on different accelerators: Comparative measurements and Monte Carlo calculations

Introduction - Volume averaging and detector mass-density effects are crucial for dosimetry in radiotherapy photon beams with small field size. Although for solid state detectors as silicon diodes and diamond detectors the two effects tend to balance each other, correction factors are in general required for field output factor measurements of small beams. Recently several studies have been published on output correction factors for the PTW 60019 microDiamond (mD) and a good agreement is observed for results referring to field sizes down to 1 cm. On the contrary results for very small field sizes are sometimes controversial thus requiring further investigation. In this study output correction factors for the microDiamond are determined by Monte Carlo (MC) calculation and applied to detector measurements (OFdet) performed by a set of ten mD detectors, in 6 MV photon beams produced by different clinical accelerators. The study mainly aims at: i) assessing up to what extent the accelerator type and collimation choice affect the mD response; ii) evaluating the variability of the dosimetric properties among the investigated mD detectors; iii) checking the consistency of MC calculation for the mD by comparing the corrected OFdet results obtained both by the set of investigated mDs and commercial silicon diodes.