Abstract
Modern external radiotherapy with photon beams takes advantage of computers, sophisticated algorithms and precise mechanics in order to let the damage close to the tumor while sparing normal tissue. Because of the accurate technique, it becomes more crucial for verification and safety issues. In this study we present the results of dosimetric evaluation of a two- dimensional Pad detector with the objective of its implementation for quality assurance in National Radiation Standard Laboratory (NRSL). The radiation dose conversion of the count reading on Pad detector is performed by means of formula and certain correction for the effect on reading of dosimeter according to the specification of the content of the dose protocols. To proceed with the correction, this research is mainly aimed at environmental temperature and pressure correction, recombination correction, and air Kerma calibration. Experiments and Geant4 simulation are designed to find recombination correction and air Kerma calibration, respectively to correct the difference in output readings between reference and user’s condition. The results show that this detector can be used for 2D dosimetry of beams. The difference of corrected statistic in this study is under 5% compared to the reference statistic provided by NRSL. Four measurements at different time of the same Co60 radiation source using the Pad detector are performed over a period of 43 days. The natural decay of Co60 source can be clearly observed from the measurements. After converting the readings of Pad detector to the same source strength by the decay formula of Co60, it is found that the difference among the four experimental measurements is < 0.4%.