The dosimetry formalism is slowly changing from air kerma to absorbed dose to water. CD High Tech chamber is widely used in India and TRS 398 does not provide Ka value for CD High Tech chamber. In this study, we determined the beam quality correction factors Ka for three cylindrical chambers of type CD High Tech, PTW 30001 and FC65, for clinical high-energy photon beams of nominal energies 6, 10 and 15 MV. Cross calibration technique of ionization chamber is used to determine the beam quality correction factors. NE 2571 chamber is used as the reference chamber. Theoretical calculations were made using the basic data available in TRS 277 / TRS 398. Experimentally obtained values of KO are compared with values of Ka from TRS 398 and TG 51. On comparison, maximum deviations of 0.4% for PTW 30001 chamber, and 0.7% for FC 65 chamber are obtained which validate this method to determine Ka at the user level. For CD High Tech chamber, it is observed that the maximum deviation of 0.3% is obtained between the calculated and the experimental values. Further, measured KO values for CD High Tech chamber are compared with NE 2505 chamber. Physical characteristics of these two chambers are comparable. A maximum deviation of 0.5% is found between the KO values of CD High Tech chamber and NE 2505 chamber. KQ values of NE 2505 can also be used for CD High Tech chamber, since the physical characteristics of both the chambers are nearly same.

The goal of the radiation therapy can be achieved if the prescribed dose is delivered to the defined target volume accurately with acceptable uncertainty. The aim of the present study was to assess the accuracy of dose delivery in brachytherapy, where measured dose was to be compared with treatment planning system (TPS) calculated dose under the comprehensive quality assurance. The therapy level ionization chamber of 0.1cc volume was placed inside the surface mould (wax medium) designed for the treatment of carcinoma of skin. The delivered dose was measured during the treatment for all fractions. The theoretical study on non-uniformity correction factors for 0.1 cc chamber and experimental study on relative transmission factor from wax to water medium that influence the measured dose were performed. The variation in TPS-calculated dose at the reference points inside chamber sensitive volume was observed to be 17.5% of the mean dose. The relative transmission factor from wax to water medium was 0.9934 per cm. The difference between the measured dose and TPS-calculated dose was 2.52%. The uncertainty in dose measurement was estimated to be + 3.8%. The accuracy of dose delivery was found well within the prescribed limit.