SU‐E‐T‐142: Impact of Quality of Tri‐Axial Cable on Radiation Dose Measurement in Proton Beam

Abstract

Purpose: Ionization chambers (IC) and electrometers are calibrated periodically at least every 2 years. However, the triaxial cables providing measuring system are neither tested nor calibrated periodically. Radiation treatment with small fields requires dose measurements with high degree of precision. In this study, we investigated the impact of different cables from various manufacturers on signals in a proton beam. Methods: Nine different commercially available cables from various vendors with different diameters and flexibility were studied. These cables were characterized by connecting to four different IC (volume 0.65–0.016cm3). The response of the cable‐connector‐IC combinationˈs were analyzed in a proton beam under the reference irradiation condition. Signals from cables were evaluated without and with connecting to an IC to investigate the effect of the quality of cable and connectors on the measured signals. Results: A significant signal is detected without an IC when irradiating the cable connector alone. Connecting to an IC, the signal is linearly related to the chamber volume with a slope of 13.23nC/cm3 for all nine cables. In a proton beam, there is no significant change in the magnitude of signals for various cables for large volume chambers. There is a 2% variation in signal for the parallel plate chamber for the different cable combination s. The signal is within ±0.02 % for large volume IC (0.65 cm3). For small volume (0.016 and 0.02cm3) chambers, the response is dominated by the quality of cable with variations up to ±0.3 % and ± 0.5 % respectively. Conclusions: The quality of cable has a larger effect on small volume chambers especially for the parallel plate chamber. Uncertainty due to cable should be considered during calibration for small volume chambers in proton beam.