Jolyon H Hendry

The Response of Haemopoietic Colony-forming Units to Single and Split Doses of γ-rays or D-T Neutrons

SummaryThe effect of single and split doses of 137Cs γ-rays or D-T neutrons on haemopoietic stem cells irradiated in donor mice was investigated, using the spleencolony technique. On the γ-ray survival-curve derived from colony-forming units from the femur, there was a shoulder characterized by an extrapolation number of 3·1 ± 0·7. Split-dose experiments demonstrated a sparing effect of γ-ray dose-fractionation, and survival curves obtained for the survivors at various times after a first dose of 200 rads (γ-rays) showed that a significant shoulder had reappeared within 5 hours of the first dose. An increased radioresistance was indicated, demonstrated by a trend towards higher D0 values for the survivors, when they were irradiated at 5 hours, 8 hours or 20 hours after a 200-rad dose of γ-rays. A lower extrapolation number of 1·7 ± 0·5 was found for D-T neutrons, and split-dose experiments demonstrated that dose-fractionation had no significant sparing effect.

Effect of Repeated Doses of X-Rays or 14 MeV Neutrons on Mouse Bone Marrow

Repeated X-irradiation (4 × 450 rads) of mice produces a decreased rate of bone marrow regeneration to a suboptimal level, compared to that after a single dose of 450 rads. 14 MeV neutrons are more effective in producing this reduced level by a factor of 1.7-1.8. The irradiated host (single 850 rads or 4 × 450 rads X-rays) is responsible for a lower growth rate of colony-forming units. The suboptimal plateau however is a cellular effect, and these are additive during endogenous repopulation. A host effect is not demonstrable in terms of changes in the colony-stimulating activity of the femur shaft in bone marrow cultures.

Daily D-T Neutron Irradiation of Mouse Intestine'

The intestinal microcolony assay technique, for measuring damage to the progenitor cell population of mouse jejunal epithelium, has been used to demonstrate the following: Single doses of collimated 14-MeV D-T neutrons (10 to 30 rad min

K values and gain factors of fast neutrons and x-rays for a mammalian cell system (cfu) in vivo.

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The effect of anoxia on the response of haemopoietic colony-forming units in different proliferative states to γ rays or D-T neutrons

) are more effective than single doses of 300-kV x-rays or Cs- 137

Neutrons and the Oxygen Effect: Corroboration of the Greater Effectiveness at High LET for Sensitization by Oxygen at Low Concentrations

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The relative spatial distributions of CFUs and CFUc in the normal mouse femur

-rays (30 to 650 rad min

The Approximation in the Formulation for Survival S = exp − (αD + βD2)

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Radiation induced hemopoiesis in adult mouse liver.

) by a factor of 1.9 to 2.3 for a reduction in crypt numbers of 50 to 80 percent. For mice irradiated at 10 cm deep in a 30-cm-deep water phantom, the above RBE values are reduced by about 9 percent. The same reduction is applicable for single doses and for four daily dose fractions. With daily fractionated irradiations (up to 5), the iso-effect curves (for 50 percent or 80 percent crypt number depopulation) are linear on a log/log plot, with slope exponents of 0.57 to 0.58 (

The response of mouse haemopoietic colony formers to acute or continuous gamma irradiation.

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