Calibration of Ionization Chambers and Dosimetric Comparison of High Energy Photon Beams Using TRS-277 and TRS-398 Protocols

Calibration of an ionization chamber is critical in dosimetry to ensure accurate, reliable, and traceable measurements of radiation dose. Without calibration, ionization chambers cannot be trusted to provide the precise and reliable measurements necessary for effective radiation dose management. And the radiation dosimetry is the measurement, calculation, and assessment of the ionizing radiation dose absorbed by matter, especially biological tissues. It plays a critical role in various fields to ensure safety, effectiveness, and regulatory compliance. According to ICRU-24, the accuracy of dose deliver to the tumour should meet ±5% of the prescribed value. 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 60Co from teletherapy, Among the protocols TRS-277 (air kerma, Nk) and TRS-398 (absorbed dose to water: ND,W) are widely used in Bangladesh. The TRS-277 involved various correction factors as the chamber calibration factor and hence uncertainty increases than TRS-398. The purpose of this research was to studies on (i) Calibration of ionization chamber (ii) Dosimetry and comparison for high energy photon beam 4 MV, 15 MV by using the two different dosimetry protocol TRS-277 & TRS-398 and (iii) Compare present measurement with international standard. The deviation of calibration factor by manufacturer’s stated value and present measurement lies in between 0.17-2.08% with maximum uncertainties of ±2.2%. The deviation of absorbed dose measurement was found within ±1.01% for 4 MV & 15 MV photon beams. TLD inter-comparison program are found excellent in agreement.