21GA/Agenda 19.231Calibration of Radiation Instruments Used in Radiation Protection and Radiotherapy in MalaysiaTaiman Bin Kadni (taimanmint.gov.my) Secondary Standard Dosimetry Laboratory (SSDL) Malaysian Institute for Nuclear Technology Research (MINT) Bangi, 43000 Kajang, MalaysiaAbstract External radiation quantity can be measured in terms of exposure, air kerma, absorbed dose, dose equivalent, ambient dose equivalent and directional dose equivalent by using radiation measuring instruments. Radiation survey instruments are usually used to determine the amount of leakage radiation from the radiation sources such as radioactive sources and x-ray machines and hence protect workers from exposure to ionizing radiation. The outputs of Cobalt-60 teletherapy units and medical linear accelerators (linac) at radiotherapy centers are determined by using dosimeters. Radiation measuring instruments such as survey meters and dosimeters need to be calibrated to ensure that they give accurate and correct reading with a certain uncertainties and to comply with the regulations imposed by the relevant authority. In Malaysia, calibration of radiation measuring instruments is legally required under the Radiation Protection (Basic Safety Standard) Regulation, 1988. The Secondary Standard Dosimetry Laboratory (SSDL) of the Malaysian Institute for Nuclear Technology Research (MINT) is the national focal point for the calibration of measuring instruments used in radiation protection and radiotherapy. The main radiation facilities include a Cobalt-60 teletherapy unit, constant potential x-ray system with a 320 kV tube, gamma calibrators, panoramic gamma irradiators, PTB beta secondary standard and an Americium-241/Be neutron calibrator. Reference standard dosimeters traceable to the Primary Standard Dosimetry Laboratory (PSDL) and the IAEA Dosimetry Laboratory are used in the calibration procedures. Dosimeters used in radiotherapy can be calibrated in terms of air kerma and absorbed dose to water to comply with an International Code of Practices for dosimetry i.e. IAEAs Technical Report Series number 277, 381 and 398. The laboratory has been accredited by the Department Standard of Malaysia (The Malaysian accreditation body) as a calibration laboratory for radiation survey meters and therapy dosimeters. Keywords : Calibration, dosimeter, radiation survey instrument, radiation sources, standardsINTRODUCTIONExternal radiation quantity can be measured in terms of exposure, air kerma, absorbed dose, dose equivalent, ambient dose equivalent and directional dose equivalent by using radiation measuring instruments. Various kinds of radiation measuring instruments such as survey meters, area monitors, personal dosimeters, contamination-monitoring instruments are used in irradiation facilities for radiation protection purposes. Implementation of the proper monitoring requires radiation-monitoring survey meters e.g. ionization chambers, Geiger-Muller (GM) counters and scintillation counters to be calibrated in terms of dose equivalent quantities. Area dosimeters or dose ratemeters should be calibrated in terms of the ambient dose equivalent, H*(10), or the directional dose equivalent, H(0.07)1. In radiotherapy centers, the radiation dosimeters are normally used for determinations of the output of Cobalt-60 teletherapy units and medical linear accelerators (linacs) and should be calibrated in terms of exposure 2, air kerma 3 or absorbed dose to water 4,5. Radiation measuring instruments need to be calibrated to ensure that they give accurate and correct reading with a certain uncertainties and to comply with the regulations imposed by the relevant authority. They should be calibrated annually 6,7 or after major repair. In Malaysia, calibration of radiation measuring instruments is a legal requirement under the Radiation Protection (Basic Safety Standard) Regulation, 19888. The SSDL-MINT was established in 1980 and is a member of the IAEA/WHO Network of SSDLs. The laboratory has acquired the status of national standard laboratory with the basic aim of improving accuracy in radiation dosimetry in the country. It is also the national focal point for the calibration of radiation measuring instruments used in radiation protection and radiotherapy. More than 1500 radiation instruments are normally calibrated every year. The laboratory has also the responsibility to ensure that the calibration services provided by the laboratory follow internationally accepted metrological standards. This is achieved by calibrating the laboratorys protection and therapy levels dosimeters against those in the Primary Standard Dosimetry Laboratories (PSDLs) or the International Atomic Energy Agency (IAEA) or by participating in the international comparison on dosimetry measurements programmes. 21GA/Agenda 19.232CALIBRATION FACILITIESa.Irradiation facilitiesThe calibration of radiation instruments used for ra