Study of dosimetric properties of a thermoluminescent system for dose audit in radiation therapy

For regular monitoring of gamma therapy units against the backdrop of insufficient provision of modern dosimetric equipment and, in some extreme cases, the lack of qualified personnel, external audits across all radiological departments are practically the only way to independently verify the accuracy of calculations of therapeutic dose delivered to patients. The relevance of this study is justified by the need to comply with the provisions of national legislative documents in the field of the nuclear energy application: The Law of Ukraine “On Human Protection against Impact of Ionizing Radiation”, The Norms of Radiation Safety of Ukraine (NRBU-97), and The State Standard of Ukraine “Measurement of Ionizing Radiation. Metrological Support. General Provisions” (DSTU 3240:2015). The requirements of these documents regarding the accuracy and reliability of dose measurements necessitate the use of high-quality detectors. Hence, among all thermoluminescent materials used for thermoluminescent dosimetric (TLD) audits of therapeutic photon beams, preference is given to a LiF, Mg, Ti phosphor (TLD-100) due to its dosimetric properties: tissue equivalence, long-term retention of dosimetric information (low fading), high sensitivity, a wide range of measurable doses, and excellent reproducibility of results in repeated measurements. The use of such detectors makes it possible to conduct regular dosimetric audits of operational gamma therapy units using the “postal dosimetry” method. This approach is of paramount importance as it allows for clinical dosimetry errors to be timely detected, enhances the quality of radiation therapy, and consequently, the standards of treatment. When conducting TLD audits, regular monitoring of dosimetric properties and parameters of both the phosphor itself and the TL measuring instrument shall be ensured, as well as a set of correction factors and the value of the expanded uncertainty shall be determined.