Consistency of calibration factor of radiotherapy dosimeters and reference dosimetry of high energy x-ray beam using two different iaea dosimetry protocols

The outcome of the radiotherapy depends on how precisional dose deliver to the treatment volume which should not be exceeded more that ± 5% of the prescribed dose. Among the several factors that effects on accurate dose delivery to the tumor, the absorbed dose measurement plays a major role. For the accuracy of dose measurement, several national and international protocols such as TRS-277, TRS-398, TG-51 and DIN-6800-2 are currently being used for the dosimetry of photon, electron and ion beams. The IAEA protocols TRS-277 (air Kerma, Nk) and TRS-398 (absorbed dose to water, ND,W) are familiar and popular that are used worldwide. The purpose of this work is to study on (a) periodical consistency of calibration factors of ionization chamber, (b) accuracy that involved in absorbed dose determination in the IAEA protocols TRS-277 and TRS-398 for high energy X-ray beam and (c) traceability of the dose measurement by participating IAEA/WHO TLD intercomparison program. A total number of 13 ionization chambers of which 12 thimble and 1 parallel plate are calibrated with 60Co in-terms ND,W factor against the reference standard of SSDL, Bangladesh. The deviation of calibration factor by manufacturer’s stated value and present measurement lies in between 0.13-3.38% with an uncertainties of ± 1.4% (coverage factor k=1). The average deviation of absorbed dose measurement between two different dosimetry protocols TRS-277 and TRS-398 were found within ± 1.59% for 4 MV and 15 MV LINAC photon beams which shows an excellent agreement with other measurement in the literature. The results obtained by the participation of IAEA/WHO intercomparison program ensures the traceability of present work with excellent agreement with IAEA standard.