THE EFFECT OF DOSE-RATE DEPENDENCE OF P-TYPE SILICON DETECTORS ON LINAC RELATIVE DOSIMETRY

Cumulative radiation damage to silicon semiconductor diode detectors c an induce dose rate dependent sensitivity, a concern in the pulsed bea m of a linac. Two p-Si diode photon detectors were used in this study, diodes A and B. Both were preirradiated by the supplier to 5 kGy, wit h diode A receiving an estimated 8 kGy from measurements, and diode B, 25 kGy. At 6 MV, the PDD measured with diode B was lower (by 4.4% at a depth of 25 cm) than diode A. Using SSD to vary the dose per pulse f rom 0.02 to 0.64 mGy/pulse, diode A was dose rate independent (within 2%), while the sensitivity of diode B changed by 13%. Silicon diode de tectors should be checked regularly against ionization chambers in the pulsed beam of a linac, especially older high-resistivity diodes that have accumulated dose from high-energy photon beams. (C) 1997 America n Association of Physicists in Medicine.