A Monte Carlo study on the PTW 60019 microDiamond detector.

Area of Science:

• Medical Physics
• Radiation Dosimetry

Background:

• Discrepancies exist in output correction factor data for microDiamond detectors in small photon beams.
• Monte Carlo (MC) simulations and measurements show disagreements, especially at very small field sizes.

Purpose of the Study:

• To investigate how microDiamond detector properties influence its output correction factor.
• To understand disagreements between MC calculations and measurements for small photon beam dosimetry.

Main Methods:

• Utilized a fluence-based decomposition of the dose conversion factor.
• Calculated stopping power ratio (water to diamond) and perturbation factors (p_int and p_ext).
• Simulated Co-60, 6 MV, and 10 MV photon beams.

Main Results:

• Output correction factors showed <2% variation for quadratic field sizes >0.3 cm.
• A clear under-response was observed for field sizes <0.5 cm, consistent with MC calculations.
• Perturbation factors p_int (volume averaging) and p_ext (substrate backscattering) explained the output correction factor's shape.

Conclusions:

• MicroDiamond detector response is well-described by dose conversion factor and fluence-based subfactors.
• MC simulations enhance understanding of small-field effects by linking output correction factor to spectral fluence changes.
• Finite active volume size and diamond substrate backscattering are key factors influencing output correction, with opposing effects.