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Alpha particles are extremely damaging to developing hemopoiesis compared to gamma irradiation
T N Jiang1, B I Lord, J H Hendry
1CRC Department of Experimental Haematology, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, England.
Radiation Research
|March 1, 1994
Summary
The current radiation protection factor for alpha particles may underestimate risks. Studies suggest a significantly higher relative biological effectiveness (RBE) for developing hemopoiesis following fetal exposure to alpha emitters like plutonium-239.
Area of Science:
- Radiobiology
- Radiation Protection
- Developmental Toxicology
Background:
- Current radiation protection guidelines use a dose-weighting factor (wR) of 20 for alpha particles, assuming their relative biological effectiveness (RBE) for deterministic effects is lower than for stochastic effects.
- However, fetal exposure to alpha-particle emitters like plutonium-239 (239Pu) has been observed to cause persistent deficits in hemopoietic stem cells, suggesting a higher RBE than currently applied.
Purpose of the Study:
- To determine a more realistic RBE for hemopoiesis following in utero exposure to alpha particles.
- To compare the effects of fetal alpha-particle irradiation with those of external gamma irradiation on the development of hemopoietic tissue.
Main Methods:
- Pregnant mice were exposed to 239Pu via placental transfer or to external 60Co gamma rays at various doses and schedules during gestation (days 13-15).
- The spatial distribution of hemopoietic stem cells in 8-week-old offspring was analyzed.
- The RBE was calculated by comparing the doses of gamma radiation required to elicit similar effects as alpha-particle irradiation.
Main Results:
- Fetal exposure to 239Pu resulted in a significantly higher RBE for hemopoiesis compared to gamma irradiation, with values ranging from 130-180 for acute gamma doses and 250-360 for continuous gamma doses.
- These in vivo RBEs for long-term effects are considerably higher than those for direct irradiation of stem cells.
- The findings indicate that a single, all-embracing weighting factor for alpha particles may be misleading and underestimate risks.
Conclusions:
- The effective RBE for developing hemopoiesis following fetal exposure to alpha emitters is substantially higher than the currently recommended wR of 20.
- Protection guidelines based on a uniform weighting factor may underestimate the risks associated with alpha-particle contamination during development.
- Further research is needed to refine radiation protection strategies for high-LET radiation, particularly concerning developmental exposures.