Small field dosimetry presents unique challenges with source occlusion, lateral charged particle equilibrium and detector size. As detector volume decreases, signal strength declines while noise increases, deteriorating the signal-to-noise ratio (SNR). This issue may be compounded by triaxial cables connecting detectors to electrometers. However, effects of cables, critical for precision dosimetry, are often overlooked. There is a need to evaluate triaxial cable and detector impacts on SNR in small fields. To evaluate the influence of triaxial cables and microdetectors on signal-to-noise ratios in small-field dosimetry. This study also aims to establish the importance of cable quality assurance for measurement accuracy.Six 9.1 m length triaxial cables from different manufacturers were tested with six microdetectors . A 6 MV photon beam (TrueBeam) was used, with a water phantom at 5 cm depth with 0.5×0.5 cm2 to 10×10 cm2 fields at 600 MU/min. Readings were acquired using cable-detector permutations with a dedicated electrometer. Cables had differing connector types, conductor materials, insulation, and diameter. Detectors had various sensitive volumes, materials, typical signals, and bias voltages.
Normalized FOFs showed 13.4% and 4.6% variation across cables for 0.5×0.5 cm2 and 1×1 cm2 fields, respectively. The maximum estimated error between any cable-detector combinations was 0.2%. No consistent FOF trend was observed with increasing cable diameter, likely due to different types of detectors used. However, absolute FOF differences of 0.9% and 0.3% were noted between cables for 0.5×0.5 cm2 and 1×1 cm2 fields, respectively.
Regular triaxial cable quality assurance is critical for precision small field dosimetry. A national protocol is needed to standardize cable evaluations/calibrations, particularly for small signals from modern detectors. This could enhance measurement accuracy and treatment delivery with advanced small-field radiotherapy techniques that promise improved patient outcomes. Further studies should expand detector and cable models tested across institutions to establish robust quality control guidelines.