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Development of a diagnostic model for inhaled promethium-147 oxide: animal studies

Description: Rats and beagle dogs were exposed by inhalation to an aerosol containing stable Sm$sub 2$O$sub 3$ tagged with $sup 145$Sm$sub 2$O$sub 3$ and $sup 143$Pm$sub 2$O$sub 3$. The animals were sacrificed at 0, 14 and 30 days post- exposure to compare the kinetics and translocation of $sup 145$Sm and $sup 143$Pm. Quantitative analysis for $sup 145$Sm and $sup 143$Pm in several tissues and excreta indicate that the two rare earth elements were mobilized and distributed similarly by the rats and dogs. Results indicate that within the error of the measurement technique, samarium acts as a carrier for promethium. The data also indicate that activities measured in fecal samples could be used to predict lung burdens of $sup 147$Pm. At activity levels and sintering temperatures employed in the rat exposures, there was sufficient activity in urine samples to permit its use as an indicator of lung burdens of $sup 147$Pm. At activity levels and sintering temperatures employed in the dog exposures, this was not the case. (auth)
Date: January 1, 1975
Creator: Shipler, D.B.; Ballou, J.E.; Griffin, B.I. & Nelson, I.C.
Partner: UNT Libraries Government Documents Department

Radiation enhancement with /sup 127/I-deoxyuridine

Description: A technique for radiation enhancement of photon radiotherapy is outlined. High LET radiations in the form of Auger electron distributions are generated by photoactivation of stable iodine incorporated as iodinated deoxyuridine (IdUrd). Of the several halogenated deoxyribonucleosides evaluated, IdUrd was found to be the only thymidine analog providing effective photoactivation. This mechanism is combined with radiation sensitization to produce an overall radiation enhancement. Calculations show that 5% replacement of Tyd in tumor DNA should multiply the biological effectiveness of low energy photons by a factor of approx. 2. Higher replacements would provide higher gains. Enhancement results from chemical sensitization by IdUrd, where it is known that effects of irradiation are multiplied by factors of from approx. 1.5 to 3 as replacement varies from 10 to 50%. Additional enhancement results from the stimulation of Auger cascades in DNA. Five percent replacement has been obtained in human tumor in vivo. Twice that has been obtained in murine tumors. Our data indicates that damage from photoactivation as well as chemical sensitization does not repair. Thus, it is anticipated that use of low dose rates associated with permanent implants of Sm-145 sources (38-45 KeV x-rays; T1/2 = 340 d) will yield an additional increase in therapeutic efficacy by a factor of from 3 to 8, compared to that obtained with acute dose rates.
Date: June 1, 1982
Creator: Fairchild, R.G.
Partner: UNT Libraries Government Documents Department

Preliminary evaluation of neutron capture cross sections for /sup 144/Sm, /sup 145/Sm and /sup 145/Pm

Description: We have made preliminary neutron-capture cross-section calculations of the Hauser-Feshbach type for the isotopes /sup 144/Sm, /sup 145/Sm, and /sup 145/Pm to investigate the production of radioactive /sup 145/Pm by neutron capture on the stable isotope /sup 144/Sm. The calculations were made for incident neutron energies from 2.5 MeV to about 1/sup -4/ or 10/sup -5/ MeV, wherever the first unbound resonance was estimated to occur in each case. At that energy, the calculated value was reduced by a somewhat arbitrary factor, and the excitation function extended down to thermal energy using a (E/sub n/)/sup -1/2/ energy dependence. Since very large uncertainties are associated with the position and magnitude of the first unbound resonance and the subsequent extrapolation back to thermal energy, the cross sections in this low-energy region should not be considered more accurate than +- a factor of 10. For incident neutron energies above each step, the calculations represent an average through the separated and overlapping resonance regions and may be accurate to better than +- a factor of 2. 18 refs., 7 figs., 5 tabs.
Date: February 13, 1986
Creator: Gardner, D.G. & Gardner, M.A.
Partner: UNT Libraries Government Documents Department

Photon-activation therapy

Description: Photon Activation Therapy (PAT) is a technique in which radiation dose to tumor is enhanced via introduction of stable /sup 127/I in the form of iodinated deoxyuridine (IdUrd). Stimulation of cytotoxic effects from IdUrd is accomplished by activation with external (or implanted) radiation sources. Thus, accumulations of this nucleoside in actively competing cellpools do not preclude therapy in so far as such tissues can be excluded from the radiation field. Calculations show that 5% replacement of thymidine (Tyd) in tumor DNA should enhance the biological effectiveness of a given photon radiotherapy dose by a factor of approx. 3. Proportionally higher gains would result from higher replacements of Tyd and IdUrd. In addition, biological response is enhanced by chemical sensitization with IdUrd. The data indicate that damage from photon activation as well as chemical sensitization does not repair. Thus, at low dose rates, a further increase in therapeutic gain should accrue as normal tissues are allowed to repair and regenerate. A samarium-145 source has been developed for PAT, with activating x-ray energies of from 38 to 45 keV. Favorable clinical results can be expected through the use of IdUrd and protracted irradiations with low energy x-rays. In particular, PAT may provide unique advantages at selected sites such as brain, or head and neck tumors. (ERB)
Date: January 1, 1982
Creator: Fairchild, R.G. & Bond, V.P.
Partner: UNT Libraries Government Documents Department