Commissioning a p-type silicon diode for use in clinical electron beams

Commissioning measurements were carried out on a p-type silicon diode detector for use in patient monitoring in high energy electron beams. Characteristics specific to the diode were examined. The variation in diode sensitivity with dose per pulse was found to be less than 1% over a range 0.069-0.237 mGy/pulse. The diode exhibited a sensitivity variation with accumulated dose of 10% per kGy and a sensitivity variation with surface temperature of 0.26%/degree C. The dependence of the diode response on the direction of the incident electron beam was investigated. Results were found to exceed the manufacturer's specifications. Output factors measured with the diode agree to within 1.5% of those measured with an NACP-02 air ionization chamber. The detector showed a variation in response with energy of 0.8% over the energy range 4-15 MeV. Prior to introducing the diode into clinical use, an assessment of beam perturbation directly behind the diode was made. The maximum reduction in local dose directly behind the diode at a depth of 1.0 cm below the surface was approximately 13% at 4 and 15 MeV.