Dosimetry and Medical Radiation Physics (DMRP)

TLD Postal Dose Audit Service

Since 1969, the IAEA’s dosimetry programme has operated a service to validate the calibration of radiation beams in developing Member States using the IAEA/WHO TLD postal dose quality audits. Originally the TLD (thermoluminescent dosimetry) service was developed for Co-60 therapy units, and since 1991 it provides audits of high-energy photon beams produced in clinical accelerators. The TLD service also monitors activities of SSDLs in radiotherapy since 1981, and it has recently been extended to auditing radiation protection standardization in SSDLs.

In both programmes, for hospitals and for SSDLs, small TL dosimeters (0.5 cm in diameter and 2.5 cm long) are distributed by mail to the participants for irradiation and upon their return, they are read in the IAEA's Dosimetry Laboratory. The TLD dose is calculated in the DMRP Section and is compared to the dose stated by the participant. The interpretation of individual TLD results involves also detailed analysis of the dosimetry procedures reported by the participants. When discrepancies occur, a follow-up action is organized to resolve the problems and correct dosimetry at the participating institutions.

The aim of the TLD audits in hospitals is to assure proper calibration of radiotherapy beams to avoid mistreatment of cancer patients and prevent radiation accidents. The service for hospitals is carried out through a collaboration between the IAEA and the World Health Organization (WHO) (PAHO in Latin America). The IAEA’s Dosimetry and Medical Radiation Physics Section is responsible for the technical aspects of the service and WHO (or PAHO) assists of the mailing and distribution of the TLD capsules to radiotherapy hospitals. This service checks approximately 800 clinical beams per year, and in many instances significant errors have been detected in the beam calibration, preventing further mistreatment of patients.

The aim of QA audits in dosimetry for SSDLs is to check the implementation of the dosimetry code of practice in order to assure proper dissemination of dosimetry standards to the end users, such as radiotherapy hospitals and radiation protection institutions. In the two parallel TLD audit programmes for the SSDLs, for radiotherapy dosimetry (Co-60 and high-energy photon beams) and for radiation protection dosimetry (Cs-137 irradiators), the dose levels differ 1000 times. The service is provided in two irradiation runs per year, each run involving 50 SSDLs active in radiotherapy dosimetry and 15 SSDLs active in radiation protection dosimetry. Due to the IAEA/WHO TLD programme, high quality of dosimetry practices is assured in the SSDLs.

The IAEA/WHO TLD service receives the support of the BIPM, Primary Standard Dosimetry Laboratories, and some advanced radiotherapy centres. These institutes provide reference irradiations of TLDs, acting as an external quality control of the service.

Data forms and instructions for participation in this service as well as a TLD irradiation video are available in English, Spanish and Russian and can be downloaded.