  The purpose of this work was to obtain output correction factors for
microDiamond and EFD-3G detectors in very small (less than 5 mm) circular
fields. We also investigated the impact of possible variations in microDiamond
detector design schematics on the calculated correction factors. Output factors
(OFs) of 6MV beams from TrueBeam linac collimated with 1.27-40mm diameter cones
were measured with EBT3 films, microDiamond and EFD-3G detectors as well as
calculated (in water) using Monte Carlo (MC) methods. Based on EBT3
measurements and MC calculations output correction factors were derived for
these detectors. MC calculations were performed for microDiamond detector in
parallel and perpendicular orientations relative to the beam axis. Furthermore,
correction factors were calculated for two microDiamond detector models,
differing by the presence or absence of metallic pins. The measured OFs agreed
within 2.4% for fields $\geqslant$10mm. For the cones of 1.27, 2.46, and 3.77mm
maximum differences were 17.9, 1.8 and 9.0%, respectively. MC calculated output
factors in water agreed with those obtained using EBT3 film within 2.2% for all
fields. MC calculated output correction factors for microDiamond detector in
fields $\geqslant$10mm ranged within 0.975-1.020 for perpendicular and parallel
orientations. MicroDiamond detector correction factors calculated for the 1.27,
2.46 and 3.77mm fields were 1.974, 1.139 and 0.982 with detector in parallel
orientation, and these factors were 1.150, 0.925 and 0.914 in perpendicular
orientation. Including metallic pins in the microDiamond model had little
effect on calculated correction factors. EBT3 and MC obtained correction
factors agreed within 3.7% for fields of $\geqslant$3.77mm and within 5.9% for
smaller cones. Including metallic pins into the detector model is not necessary
as their presence/absence had no effect on calculated correction factors.
