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

Commissioning measurements were carried out on a p-type silicon diode detec tor fur use in patient monitoring in high energy electron beams. Characteri stics specific to the diode were examined. The variation in diode sensitivi ty with dose per pulse was found to be less than 1% over a range 0.069-0.23 7 mGy/pulse. The diode exhibited a sensitivity variation with accumulated d ose of 10% per kGy and a sensitivity variation with surface temperature of 0.26%/degrees C. The dependence of the diode response on the direction of t he incident electron beam was investigated. Results were found to exceed th e manufacturer's specifications. Output factors measured with the diode agr ee 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 e nergy range 4-15 MeV. Prior to introducing the diode into clinical use, an assessment of beam perturbation directly behind the diode was made. The max imum 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. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01101-3].