The dependence ofNKRversus KR: the initial, thermal, volumetric recombination and screening effect on the efficiency of collected charges on the calibration of si HDR1000 plus well chambers with192Ir HDR sources.

By using the statistical techniques of the ANOVA means test and regression, it was found that theNKRcalibration factor of Standard Imaging (SI) model HDR 1000 plus chambers presents a quadratic dependence with the Reference air kerma rateKR(from 6.9 mGy h-1to 43.9 mGy h-1). In order to understand and correct this dependency one model is presented for total recombination:ks=I300I150=1+kini+kd+kvol·I300+kscreen·I3002,wherekiniis the initial recombination,kvolthe thermal diffusion recombination,kvolthe volumetric recombination andkscreenthe screening for the currents/charges collected at the potential differences of 300 and 150 V. In conclusion, the total recombinationksis composed by onekiniwith a constant contribution of 0.019%, onekdcontribution of 0.017%, onekvol·I300contribution from 0.022% to 0.138%, and thekscreen·I3002effects from 0.002% to 0.09% in the range ofK̇Rrate above. However, when this model forksis applied to try to correct the quadratic dependence of theNKRversusKR,explicitly there is no improvement in the variation range of 0.5% of theNKRversusKR.Nonetheless, it allows to obtainNKRvalues consistent with auc ≤ 0.7%, which is less than 1.25% reported in the literature by ADCLs or SSDLs.

PROFICIENCY TEST OF THE SSDL-ININ-MEXICO FOR THE CALIBRATION OF WELL-TYPE CHAMBERS WITH HDR 192IR SOURCES USING TWO DIFFERENT DOSIMETRY CODES OF PRACTICE FOR THE DETERMINATION OF REFERENCE AIR KERMA RATE KR.

The results of the comparison between SSDL-ININ and SSDL-CPHR (pilot laboratory) demonstrates the competence of the SSDL-ININ for the performance of the KR in 192Ir. The RININ/CHPR ratio for the calibration coefficients is 0.989 ± 0.005. The comparison uses three SI-HDR 1000-Plus as transfer chambers, series: A02423, A941755 and A973052. CPHR used a secondary standard PTW 3304 chamber, s/n 154, calibrated at PTB and ININ employed a secondary standard SI-90008 s/n A963391, calibrated at NPL. To determine KR, the SSDL-CPHR used the IAEA TEC-DOC-1274 and the SSDL-ININ used the IPEM (UK) code of practice. The latter uses a correction factor by source's geometry, ksg. The results show that both codes are equivalent; however, for the use of well chambers in the highlands or in locations with reduced atmospheric pressure, it is needed to apply an additional factor k'P, or, to design a well chamber with air-equivalent walls for the application of the conventional kPT.

Comparison of Hp(0.07, 0°) for 90Sr/90Y Beta Radiation with CaF2:Dy TLD-200 Dosimeters.

The results for the comparison of Hp(0.07,0°) in 90Sr/90Y, carried out by the SSDL-ININ (pilot) and CPHR, are presented. Four calibration curves (CCs) are constructed with 32 TLD-200 dosimeters irradiated on a PMMA phantom. The CCs, TLD's Response RTLD (nC) vs Hp(0.07,0°), are in the range 0.2-100 mSv. The SSDL-ININ rate Hp(0.07, 0°) value is (43.85 ± 0.57) µSv s-1 obtained with a primary extrapolation chamber serial 040. These same dosimeters are irradiated at the CPHR with a rate of Hp(0.07, 0°) = (14.94 ± 0.36) µSv s-1, also calibrated with another primary standard extrapolation chamber serial 105. After irradiation at CPHR, the dosimeters are returned to the SSDL-ININ for reading, and then irradiated again to construct the fourth CC (CC4). The comparison is based on a modification of the standard ANSI/HPS N13.11-2009, where the reference values are [Hp]ININ,ref. For the values of [Hp]CPHR the statistics bias B = 0.002; standard deviation, S = 0.099; and tolerance level L = 0.099 are determined. The homoscedasticity test is performed for the variances associated to the mean performance quotientB.

A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry.

INTRODUCTION: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detector's response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E¯(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality indexQ(BT)(E¯), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, Dw, around BT sources. MATERIALS AND METHODS: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT)(E¯)=TPR10(20)(E¯) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT)(E¯)=Dprim(r=2cm,θ0=90°)/Dprim(r0=1cm,θ0=90°), utilizing precise primary absorbed dose data, Dprim, from source reference databases, without additional MC-calculations. RESULTS AND DISCUSSION: For BT photon sources used clinically, Q(BT)(E¯) enables to determine the effective mean linear attenuation coefficient µ¯(E) and thus the effective energy of the primary photons Eprim(eff)(r0,θ0) at the TG-43 reference position Pref(r0=1cm,θ0=90°), being close to the mean total photon energy E¯tot(r0,θ0). If one has calibrated detectors, published E¯tot(r) and the BT radiation quality correction factor [Formula: see text] for different BT radiation qualities Q and Q0, the detector's response can be determined and Dw(r,θ) measured in the vicinity of BT photon sources. CONCLUSIONS: This novel brachytherapy photon radiation quality indexQ(BT) characterizes sufficiently accurate and precise the primary photon's penetration probability and scattering potential.