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S M Seltzer

Publications and source records attributed to S M Seltzer.

34 records · Page 2Linked to original sources
PubMed1994

EPR dosimetry of cortical bone and tooth enamel irradiated with X and gamma rays: study of energy dependence.

Previous investigators have reported that the radiation-induced EPR signal intensity in compact or cortical bone increases up to a factor of two with decreasing photon energy for a given absorbed dose. If the EPR signal intensity was dependent on energy, it could limit the application of EPR spectrometry and the additive reirradiation method to obtain dose estimates. We have recently shown that errors in the assumptions governing conversion of measured exposure to absorbed dose can lead to similar "apparent" energy-dependence results. We hypothesized that these previous results were due to errors in the estimated dose in bone, rather than the effects of energy dependence per se. To test this hypothesis we studied human adult cortical bone from male and female donors ranging in age from 23 to 95 years, and bovine tooth enamel, using 34 and 138 keV average energy X-ray beams and 137Cs (662 keV) and 60Co (1250 keV) gamma rays. In a femur from a 47-year-old male (subject 1), there was a difference of borderline significance at the alpha = 0.05 level in the mean radiation-induced hydroxyapatite signal intensities as a function of photon energy. No other statistically significant differences in EPR signal intensity as a function of photon energy were observed in this subject, or in the tibia from a 23-year-old male (subject 2) and the femur from a 75-year-old female (subject 3). However, there was a trend toward a decrease (12-15%) in signal intensity at the lowest energy compared with the highest energy in subjects 1 and 3. Further analysis of the data from subject 1 revealed that this trend, which is in the opposite direction of previous reports but is consistent with theory, is statistically significant. There were no effects of energy dependence in the tooth samples.

Adult↗
PubMed1993

Exposure-to-absorbed-dose conversion for human adult cortical bone.

The conversion of measured exposure to absorbed dose at a point in bone, under conditions of electron equilibrium, involves a factor (the f-factor) which is proportional to the ratio of the spectrum-averaged photon energy-absorption coefficient for bone to that for air. This paper gives mass energy-absorption coefficients and f-factors for three compositions of human adult compact or cortical bone recommended in publications by the ICRU and the ICRP, for photon energies from 1 keV to 1.5 MeV. Spectrum-averaged f-factors for a number of calibration x-ray beams ranging from 10 to 250 kVp have been calculated and compared to corresponding results obtained with the use of an equivalent photon energy derived from the measured thickness of the half-value layer. At low photon energies (approximately less than 200 keV), the new f-factor results reflect: (a) the rather large differences due to the differing calcium contents among the recommended compositions for bone: and (b) the generally poor predictions obtained when replacing a broad energy spectrum by an equivalent photon energy.

Adult↗
PubMed1993

Calculation of photon mass energy-transfer and mass energy-absorption coefficients.

Calculations of mass energy-transfer and mass energy-absorption coefficients for photon energies from 1 keV to 100 MeV have been developed, based on a re-examination of the processes involved after the initial photon interaction. The probabilities for the initial interaction are from the current photon interaction cross-section database at the National Institute of Standards and Technology. The calculations then take into account (1) electron binding effects on the Compton-scattered photon distribution; (2) the complete cascade of fluorescence emission after ionization events in any atomic subshell, including those associated with incoherent scattering and triplet production; and (3) the radiative energy losses of the secondary electrons and positrons slowing down in the medium, including the emission of bremsstrahlung, characteristic X rays from impact ionization, and positron in-flight as well as at-rest annihilation quanta. Consideration of the processes in (3) goes beyond the continuous-slowing-down approximation and includes the effects of energy-loss straggling. Results for the mass energy-absorption coefficient are compared with those from recent tabulations.

Absorption↗