Abstract

LOAIZA CALDERON, S.P.  and  ALVAREZ ROMERO, J.T.. Calibración de polvo TLD-100 para energías de ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir y RX de 250, 50 k Vp en dosis absorbida en agua con fines de control de calidad dosimétrico para braquiterapia de alta tasa de dosis. Rev. mex. fis. [online]. 2006, vol.52, n.5, pp.413-421. ISSN 0035-001X.

To help solve the traceability and quality control dosimetric problems for the users of ¹⁹²Ir sources in the Mexican Republic, the Secondary Standard Dosimetric Laboratory at ININ to calibrated a batch of powder TLD-100 (LiF:Mg,Ti) in terms of absorbed dose to water D_w for the following radiation sources: ⁶⁰Co, ¹³⁷Cs and RX 250 and 50 kVp. Later on, the calibration is interpolated to obtain the ¹⁹²Ir. The calibration radiation field is carried out with the following protocols: For the ⁶⁰Co, OIEA TRS 398 protocol employing a secondary standard Farmer chamber PTW N30013, calibrated on D_w at the NRC (Canada). For ¹³⁷Cs the AAPM TG 43 protocol is used, in terms of air kerma strength Sk determined by the air kerma K_a measured with a secondary standard chamber type thimble NE2611 traceable to the NIST (USA). For Rays X 250 and 50 kVp, the protocol AAPM TG 61 using a tertiary standard Farmer chamber PTW 30001, with traceability to the LCIE (France) on air kerma K_a. The calibration curves are built for the TLD response R_TLD vs D_w, they are fitted by means of a least squares fit technique with a second degree polynomial that corrects the supralinearity response. The curves are validated by the lack of fit test, and the Anderson Darling normality test. Later on, the sensibility factors are interpolated for the sources of ¹⁹²Ir: MicroSelectron and VariSource. Two capsules are sent to two hospitals to verify a nominal D_w = 2 Gy, in the first one an underestimate of the D_w is obtained, and in other one an overestimation is presented. Finally, the expanded uncertainty associated to D_wand the F_s are calculated.

Keywords : TL Dosimetry; TLD-100; Brachytherapy; HDR; absorbed dose to water; ¹⁹²Ir.