International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Linear Accelerators and Cobalt units are common source of radiation for external radiotherapy. In Vivo Dosimetry (IVD) is a real time quality control set of methods used in cancer treatment clinics to assure that dose is delivered as prescribed to tumor, while surrounding healthy tissue is spared. Silicon Diode detectors are among most popular detectors used for IVD. In certain clinical conditions, both entrance and exit dose measurements are needed, for quality insurance, to calculate the dose received by tissue or organ inside patient’s body. Response of silicon diode detectors depends on multiple factors therefore prior of use in IVD each detector needs to be calibrated and corresponding factors of correction need to be calculated. Correction factors are needed to calculate dose for different field sizes, angle between beam axis and couch axis, skin to source distance (SSD), temperature etc. In this work we present our calculation of exit dose calibration factors for six silicon diode detectors made by PTW Frieburg Germany. Diodes are calibrated for exit dose under either 6 MVor 18 MV beam of photons as designated by manufacturer. Further we study dependence of response of individual diodes on distance from source and calculate corresponding correction factors. It was found that exit dose SSD dependence is pronounced and correction factors are necessary for exit dose IVD with diode detector in clinics.

Semiconductor silicon diodes are used widely as detectors in oncology radiation centers for In Vivo Dosimetry (IVD). IVD is the ultimate method used in cancer treatment centers to detect possible errors in dose delivery. Diode dosimetry is based on the linearity of diode current with dose. Number of carriers taking part in diode current, is proportional to dose received for practical dose range. However, carrier lifetime and mobility are temperature dependent. In addition dark current increases with temperature. Correction factors are therefore needed in order to offset dark current influence, whenever dose is measured at a temperature different from calibration or reference temperature. We investigate the effect on signal for three PTW diodes in a 18 MV photon beam generated by Elekta Synergy Accelerator and find correction factors for clinical range of temperatures.