TLD Postal Dose Quality Audit Intercomparison for Megavolts Photon Beam of Radiotherapy Centers in Bangladesh

Abstract

A postal dose intercomparison program based on the thermo-luminescence dosimeter (TLD) was carried in order to investigate and reduce uncertainties involved in the measurement of absorbed dose, and to improve the accuracy of dose measurement at different radiotherapy centers in Bangladesh. The intercomparison program was organized by the Secondary Standard Dosimetry Laboratory (SSDL) with the assistance of the IAEA/WHO postal dose intercomparison network. A set of three TLDs (encapsulated LiF powder) including a control was sent to the participating radiotherapy centers for irradiation with 2 Gy of absorbed dose to water. The measurements were made for 60Co and megavolts X-ray beam. Thirteen beams in total were checked. Deviation of ±5% between stated and evaluated dose was considered to be acceptable for 60Co and 6MV X-ray beam. The result of 60Co beam of two centers exceeds the acceptance limit. The maximum deviation was -8.6% with an uncertainty of 1.8% i.e., the ratio of intercomparison dose to locally measured dose was 1.09. We discussed the immediate and corrective action to minimize the discrepancies. For ten 60Co beam measurements, a mean valued of the ratio of intercomparison dose to locally stated dose was 0.988 with a standard deviation of 0.031. The importance of a proper ongoing quality assurance program is essential in maintaining the consistency and the uniformity of absorbed dose measurement for the precision dose delivery to the patient.