Low dose fetal irradiation, chromosomal instability and carcinogenesis in mouse

Cancer risks associated with external radiation from diagnostic imaging procedures

The 600% increase in medical radiation exposure to the US population since 1980 has provided immense benefit, but increased potential future cancer risks to patients. Most of the increase is from diagnostic radiologic procedures. The objectives of this review are to summarize epidemiologic data on cancer risks associated with diagnostic procedures, describe how exposures from recent diagnostic procedures relate to radiation levels linked with cancer occurrence, and propose a framework of strategies to reduce radiation from diagnostic imaging in patients. We briefly review radiation dose definitions, mechanisms of radiation carcinogenesis, key epidemiologic studies of medical and other radiation sources and cancer risks, and dose trends from diagnostic procedures. We describe cancer risks from experimental studies, future projected risks from current imaging procedures, and the potential for higher risks in genetically susceptible populations. To reduce future projected cancers from diagnostic procedures, we advocate the widespread use of evidence-based appropriateness criteria for decisions about imaging procedures; oversight of equipment to deliver reliably the minimum radiation required to attain clinical objectives; development of electronic lifetime records of imaging procedures for patients and their physicians; and commitment by medical training programs, professional societies, and radiation protection organizations to educate all stakeholders in reducing radiation from diagnostic procedures.

Tracing radiation induced genomic instabilityin vivoin the haemopoietic cells from fetus to adult mouse

The present experiment was aimed at studying the delayed expression of fetal irradiation induced genomic instability in the mouse haemopoietic cells in vivo. The abdominal area of 14 day pregnant Swiss albino mice was exposed to 0-1.5 Gy of gamma radiation. Chromosomal aberrations were studied in three passages of spleen colonies (short-term repopulating stem cells, STRSC) derived from 24 h post-irradiation fetal liver cells and in the 1-20 months postpartum bone marrow (long-term repopulating stem cells, LTRSC). Irradiation produced a significant and dose-dependent increase in the aberrant metaphases in the first passage spleen colony (CFU-S1) cells, which decreased in subsequent passages and reached normal levels by the third passage (CFU-S3). Bone marrow at 1-6 months postpartum showed similar chromosomal picture in the 0 Gy control and after 0.5-1.5 Gy, but there was a clear increase in aberrant cells from 9 months postpartum in the irradiated groups. Some mice in all irradiated groups showed a 2.5- to 5-fold increase in peripheral leukocyte counts. Bone marrow of these animals exhibited severe aneuploidy, the chromosome number ranging from less than 1n to 6n at 20 months of age. Our results indicate that unstable chromosome aberrations induced in the fetal haemopoietic STRSC are eliminated during subsequent cell divisions. However, genomic instability induced in the LTRSC persists and is expressed as chromosomal aberrations at advanced ages. Induction of chromosome aneuploidy could be an early step in the chain of events leading to adult leukaemia after prenatal irradiation.

Radiosensitivity of the developing haemopoietic system in mammals and its adult consequences: animal studies

The haemopoietic system in the developing mammal is very sensitive to the damaging effects of ionizing radiation. Epidemiological studies have established a strong association between obstetric exposure to diagnostic radiation and an increase in the incidence of childhood leukaemia and between low dose gamma irradiation during the early fetal period and mental retardation in children. It has been suggested that insufficient oxygen supply to the developing brain due to radiation induced damage to fetal haemopoietic tissue has a role in inducing the severe mental retardation observed in the Japanese children exposed to atom bomb radiation in utero. Experimental studies have shown that X- and gamma irradiation of pregnant mice with <1 Gy during the late organogenesis or fetal period caused chromosome damage and significant depletion in the fetal haemopoietic progenitor cells and led to haematological disorders in the adults. The present paper reviews the experimental findings on the effect of pre-natal irradiation on the fetal haemopoietic system and its long-term consequences.