A thermoluminescence dosimetry (TLD) system was characterised at SSDL-ININ to verify the air-kerma strength (S(K)) and dose-to-water (D(W)) values for (137)Cs sources used in low dose rate (LDR) brachytherapy treatments at the Hospital General de Mexico (HGM). It consists of a Harshaw 3500 reader and a set of TLD-100 powder capsules. The samples of TLD-100 powder were calibrated in terms of D(W) vs. nC or nC mg(-1), and their dose response curves were corrected for supralinearity. The D(W) was calculated using the AAPM TG-43 formalism using S(K) for a CDCSM4 (137)Cs reference source. The S(K) value was obtained by using a NE 2611 chamber, and with two well chambers. The angular anisotropy factor was measured with the NE 2611 chamber for this source. The HGM irradiated TLD-100 powder capsules to a reference dose D(W) of 2 Gy with their (137)Cs sources. The percent deviations between the imparted and reference doses were 1.2% < or = Delta < or = 6.5%, which are consistent with the combined uncertainties: 5.6% < or = u(c) < or = 9.8% for D(W).

Abstract. According to the Mutual Recognition Agreement (MRA) of the International Committee of Weights and Measures (CIPM) the Secondary Standard Dosimetry Laboratory (SSDL) of the Instituto Nacional de Investigaciones Nucleares (ININ) is the Designated Institute (DI) by the Centro Nacional de Metrología (CENAM) before the CIPM to establish and maintain the national standard for dosimetric quantities of ionizing radiation. In particular, the SSDL's main purpose is to provide assistance for quality assurance (QA) and calibration services in terms of absorbed dose to water ( ) to radiotherapy centers in Mexico, that employ external 60 Co photon beams or high-energy x-rays for treatment of malignant neoplasia. Specifically, to achieve tumor control in the patient the absorbed dose should be given with an expanded uncertainty ( = 2) 5%. Hence the SSDL-ININ has developed the 's Calibration and Measurement Capabilities (CMC) for the calibration of ionization chambers, by a coefficient calibration International Atomic Energy Agency Technical Report Series 398 international practice code.

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