In utero haemopoietic sensitivity to alpha, beta or X-irradiation in CBA/H mice.

PURPOSE: To assess in utero sensitivity to x-rays, alpha-emissions from plutonium-239 and beta-emissions from tritium in terms of induction of chromosomal aberrations in bone marrow cells. MATERIALS AND METHODS: CBA/H mice were exposed to a single dose of X-rays (0.5Gy) on either day 7 or day 14 of pregnancy or given (239)Pu (100 kBq kg(-1)) by intraperitoneal injection on either day 6 or day 13. Tritium was administered to mice throughout pregnancy as either tritiated water, ad libitum in drinking water (total intake averaged 130 MBq), or as homogenized tritiated cress, administered by gastric intubation (total 60 MBq). Irradiated and unexposed control mice and their offspring were sacrificed at 2-8 weeks after birth. Direct metaphase preparations from femoral bone marrow cells from mothers and offspring were used for G-band analysis. RESULTS: The incidence of stable aberrations was significantly and similarly increased in neonatal and maternal marrow samples after exposure to X-rays, (239)Pu or (3)H. The estimated average bone absorbed doses from (239)Pu in pregnant females were similar to the X-ray dose of 0.5 Gy, suggesting a low RBE for alpha-irradiation in adults. The similar levels of damage observed in neonates after X-irradiation and 239Pu exposure are indicative of greater in utero sensitivity to alpha-irradiation since the overall estimated in utero alpha-particle doses to haemopoietic tissue were much lower. In utero doses from (3)H and corresponding maternal doses were around 0.5Gy, showing no evidence of greater in utero sensitivity, no significant difference between the effects of the two forms of tritium, and were consistent with an RBE value of 1-2. CONCLUSIONS: Comparison of stable aberration yields in haemopoietic cells suggests a greater sensitivity to alpha-particles from (239)Pu than X-rays or beta-particles from (3)H for irradiation in utero but a low RBE value in adults.     

Chromosomal instability in haemopoietic cells of the foetus, mother and offspring after in utero irradiation of the CBA/Ca mouse.

PURPOSE: The present study was conducted to test the susceptibility of the mouse foetus to transmit chromosomal instability to the haemopoietic stem cells of offspring after in utero X-or plutonium-239-irradiation. MATERIALS AND METHODS: Pregnant CBA/Ca-mice were injected with 80 kBq/kg 239Pu or X-irradiated with 1 Gy X-rays on days 13 or 14 of gestation. CFU-A cultures were grown from haemopoietic stem cells sampled from foetal liver and the bone marrow from the offspring and from the mother. Non-clonal, unstable chromosomal aberrations were scored in metaphases from individual stem cell colonies. RESULTS: The relative excess (RE) of unstable chromosomal aberrations in foetal liver cells irradiated with 1 Gy X-rays increased from 1.6 at day 2 up to 2.7 at day 4 after irradiation. In the bone marrow cells from the mother, this value was 1.8 (average from cells sampled at days 3 and 14 after irradiation). After injection of the pregnant mice with 235Pu, the yield of unstable chromosomal aberrations per cell was 0.14+/-0.03 (RE approximately 10) in descendants of bone marrow cells from the mother, 0.11+/-0.02 (RE = 10) in descendants of foetal liver cells and 0.16+/-0.05 (RE = 10) in descendants of bone marrow cells from the offspring. CONCLUSIONS: From the numerical analysis of non-clonal, unstable aberrations in haemopoietic cells from the foetus, the mother and the offspring after in utero irradiation, it was concluded that in utero irradiation of the CBA/Ca mouse was not more efficient in inducing chromosomal instability in the offspring than in the foetus or the mother. All three cell populations exhibited a similar degree of unstable aberrations, both in terms of the absolute numbers of non-clonal aberrations and in terms of relative excess compared with unexposed controls.     

Alpha-particles Induce Preneoplastic Transformation of Rat Tracheal Epithelial Cells in Culture

Summary

To characterize the potential role of high-l.e.t. radiation in respiratory carcinogenesis, the cytotoxic and transforming potency of 5·5 MeV α-particles from electroplated sources of ²³⁸Pu were determined using primary cultures of rat tracheal epithelial cells. The α-particle response was compared to the effects of 280 kVp X-rays and of the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine. Increasing the α-particle dose caused an exponential decrease in survival with a D₃₇ of 1·6 Gy. X-rays also caused a dose-dependent decrease in survival (D₃₇ = 3·6 Gy) but the survival curve had a significant shoulder. The RBE for cell killing by α-particles versus X-rays varied with dose, and ranged between 4 and 1·5 for α doses in the range 0·2–4 Gy. At equally toxic doses (relative survival 0·18–0·2), all three agents induced similar frequencies of preneoplastic transformation. For preneoplastic transformation induced by doses of α- and X-radiations giving 80 per cent toxicity, an α RBE of 2·4 was derived. The similar RBEs for cell killing and for preneoplastic transformation suggest an association between the type or degree of radiation-induced damage responsible for both cell killing and cell transformation.     

The Combined Effects of α-particles and X-rays on Cell Killing and Micronuclei Induction in Lung Epithelial Cells

Summary

Understanding how cellular damage produced by high-linear energy transfer (LET) radiation interacts with that produced by low-LET is important both in radiation therapy and in evaluating risk. To study such interactions, rat lung epithelial cells (LEC) were grown on Mylar® films and exposed to both X-rays and α-particles, separately or simultaneously. Cell killing, and the numbers of binucleated cells and micronuclei, were measured as indicators of damage. X-rays and α-particles given separately caused dose-related increases in cell cycle time, with α-particles producing greater mitotic delay than X-rays. Damage from α-particles and X-rays given simultaneously did not interact to alter further the cell cycle. Cell survival data following exposure to X-rays and α-particles, combined or individually, were fitted by linear-quadratic models. Survival curves following exposure to α-particles only, or to 1·0 Gy α-particles plus graded X-ray doses, were adequately described using only the linear (α) term of a linear-quadratic model with α coefficients of 0·9 ± 0·04 and 1·03 ± 0·18 Gy^?1, respectively. Survival following exposure to X-rays only or to 0·06 Gy α-particles combined with X-rays was best fitted using both α and β terms of the linear-quadratic model (0·12 ± 0·03)D + (0·007 ± 0·002)D² and (0·57 ± 0·08)D + (0·3 ± 0·02)D², respectively. The numbers of micronuclei produced by exposure to α-particles or X-rays alone increased linearly with dose, with slopes of 0·48 ± 0·07 and 0·19 ± 0·05 micronuclei/binucleated cell per Gy for α and X-rays, respectively. Simultaneous exposure to graded levels of X-rays and a constant α dose of either 1·0 or 0·06 Gy increased micronuclei frequency, with a slope of 0·74 ± 0·05 or 0·58 ± 0·04 micronuclei/binucleated cell per Gy, respectively. These slopes are similar to that produced by α-particles alone. These studies demonstrated that both cell killing and the induction of micronuclei were increased by combined exposure compared with that predicted for separate exposures.     

Long-term effects of plutonium-239 and radium-224 on the distribution and performance of pluripotent haemopoietic progenitor cells and their regulatory microenvironment.

Experiments are described which investigate the long-term damage to haemopoietic progenitor cells (CFU-S) and their microenvironment in mouse marrow resulting from the administration of leukaemogenic amounts of plutonium-239 and radium-224. 239Pu (35 Bq g-1 body weight) and 224Ra (555 Bg g-1 body weight) were injected into 10-12-week-old mice, and numbers, proliferative activity and self-renewal capacity of CFU-S were measured at different locations in femoral marrow at intervals over the following 2 years. Parallel measurements were also made of the quality of the haemopoietic microenvironment by ectopic transplantation of bone marrow cells. There was some recovery from the initial effects of 239Pu on CFU-S numbers after 3-6 months, although the recovery was not maintained in all marrow fractions. Following 224Ra administration there was an initial transient increase in CFU-S numbers in the fraction of marrow furthest from bone surfaces but a considerable depression in numbers in other regions of marrow; there was no recovery between 3 and 6 months and subsequent recovery was not complete in all regions of marrow. The differential responses of CFU-S and the haemopoietic microenvironment following 224Ra or 239Pu administration seemed in some ways related to the metabolism of the radionuclides. There was a profound reduction in the ability of marrow to generate ossicles when transplanted under the kidney capsule as a result of the administration of either 224Ra or 239Pu, with only transient recoveries from the effects of 239Pu at 4 days and at 3 months after injection.     

Tumorigenic target cell regions in bone marrow studied by localized dosimetry of 239 Pu, 241 Am and 233 U in the mouse femur

Purpose : To study the temporal change in microdistribution of plutonium-239, americium-241 and uranium-233 in the mouse distal femur and to compare and combine calculated radiation doses with those obtained previously for the femoral shaft. Also, to relate doses to relative risks of osteosarcoma and acute myeloid leukaemia. Materials and methods : Computer-based image analysis of neutron-induced and α -track autoradiographs of sections of mouse femora was used to quantify the microdistribution of 239 Pu, 241 Am and 233 U from 1 to 448 days after intraperitoneal injection. Localized dose-rates and cumulative doses over this period were calculated for different regions of the marrow spaces in trabecular bone. The results were then combined with previous data for doses to the cortical marrow of the femoral shaft. A morphometric analysis of the distal femur was carried out. Results : Initial deposition on endosteal surfaces and dose-rates near to the trabecular surfaces at 1 day were two to four times greater than corresponding results for cortical bone. Burial was most rapid for 233 U, about twice the rate in cortical bone. As in cortical bone, subsequent uptake into the marrow was seen for 239 Pu and 241 Am but not 233 U. Cumulative doses to 448 days for different regions of trabecular marrow were greater than corresponding values for cortical marrow for each radionuclide. Combined doses reflected the greater overall volume of cortical marrow. Conclusions : Cumulative radiation doses to the 10 μ m thick band of marrow adjacent to all endosteal surfaces were in the ratio of ~7:3:1 for 239 Pu: 241 Am: 233 U. This ratio is not inconsistent with observed incidences of osteosarcoma induction by the three nuclides. Analysis of doses to different depths of marrow, however, showed that although ratios were probably not significantly different to that for a 10 μ m depth, better correlations with osteosarcomagenic risk were obtained with 20-40 μ m depths. For acute myeloid leukaemia, the closest relationship between relative risk and doses was obtained by considering only the central 5-10% of marrow, which gave a dose ratio of ~12:11:1 for 239 Pu: 241 Am: 233 U respectively.     

Alpha-irradiation of haemopoietic tissue in pre- and postnatal mice: 2. Effects of mid-term contamination with 239Pu in utero.

The distribution of 239Pu in various tissues of foetal and postnatal offspring of pregnant mice, injected i.v. at 13 days gestation with 30 kBq 239Pu/kg (in some cases with 10 or 100 kBq/kg), together with the numbers of haemopoietic progenitors in the bone marrow, spleen and liver, were measured through to 1 year post-partum. The quality of the haemopoietic microenvironment in these mice was also measured using the renal-capsule implant method. The largest radiation dose received by any haemopoietic organ was that in the liver, amounting to 10-14 mGy, as reported previously. In spite of normal numbers of haemopoietic spleen colony-forming cells (CFC-S) in the liver and seeding, at birth, into the bone marrow where the level of plutonium was minimal, a long-term deficit in their number rapidly developed. The development of the stromal microenvironment, however, was also deficient, suggesting that the dose of alpha-irradiation to the foetal liver was sufficient to cause sublethal damage in those cells destined to become the precursors of the supportive haemopoietic microenvironment in bone marrow and spleen. The results of this study suggest that although the placenta affords significant shielding to the tissues of the developing foetus from maternal contamination, the long-term effects on haemopoiesis are comparable to those in mice contaminated as adults. This further implies that the developing haemopoietic tissues are exquisitely sensitive to 239Pu contamination.     

Long-term Effects of Plutonium-239 and Radium-224 on the Distribution and Performance of Pluripotent Haemopoietic Progenitor Cells and Their Regulatory Microenvironment

Summary

Experiments are described which investigate the long-term damage to haemopoietic progenitor cells (CFU-S) and their microenvironment in mouse marrow resulting from the administration of leukaemogenic amounts of plutonium-239 and radium-224. ²³⁹Pu (35 Bq g^?1 body weight) and ²²⁴Ra (555 Bg g^?1 body weight) were injected into 10–12-week-old mice, and numbers, proliferative activity and self-renewal capacity of CFU-S were measured at different locations in femoral marrow at intervals over the following 2 years. Parallel measurements were also made of the quality of the haemopoietic microenvironment by ectopic transplantation of bone marrow cells. There was some recovery from the initial effects of ²³⁹Pu on CFU-S numbers after 3–6 months, although the recovery was not maintained in all marrow fractions. Following ²²⁴Ra administration there was an initial transient increase in CFU-S numbers in the fraction of marrow furthest from bone surfaces but a considerable depression in numbers in other regions of marrow; there was no recovery between 3 and 6 months and subsequent recovery was not complete in all regions of marrow. The differential responses of CFU-S and the haemopoietic microenvironment following ²²⁴Ra or ²³⁹Pu administration seemed in some ways related to the metabolism of the radionuclides. There was a profound reduction in the ability of marrow to generate ossicles when transplanted under the kidney capsule as a result of the administration of either ²²⁴Ra or ²³⁹Pu, with only transient recoveries from the effects of ²³⁹Pu at 4 days and at 3 months after injection.     

Quantification of radiation induced DNA double-strand breaks in human fibroblasts by PFGE: testing the applicability of random breakage models

Purpose : To assess the applicability of methods of quantification of double-strand breaks (DSB) based on the random breakage paradigm, measuring yield and distribution of DSB induced by varying radiation quality. Material and methods : 240 kVp X-rays and 238 Pu α -particles were used to induce DSB in AG01522B primary human fibroblasts. DNA molecular weight distributions were resolved by means of three pulsed-field gel-electrophoresis (PFGE) protocols, which, when combined together, allowed separation and quantification of double-stranded fragments between 5.7 Mbp and 12 kbp. Several analytical methods quantified the DSB yields. Results : Data showed significant differences in the fragmentation patterns according to radiation quality. For both X-rays and α -particles, it was observed that the shape of the fragmentation profiles deviates from the prediction of a random breakage mechanism. This is in contrast to other studies where sparsely ionizing radiations appeared to distribute breaks uniformly throughout the genome. Deviations from random breakage were more evident after high linear energy transfer (LET) radiation, which showed an excess of breaks <1 Mbp and a deficit in the production of fragments >1 Mbp, a value that could be dose-dependent. Conclusions : Current methods of DNA fragmentation analysis after induction of DSB may lead to contradictory conclusions on both DSB yields and distributions. This study showed that the application of different DSB quantification methods, derived from random breakage or supported by its concepts, resulted in different radiation biological effectivenesses (RBE) for the induction of DSB, depending on how these methods were employed. To compare experimental results from different laboratories, care should be taken to provide as many details as possible about the application of methods of quantification of DNA damage. For all the methods used, total DSB yields resulted in RBE less than those for mutation induction or reproductive cell death, suggesting that total DSB yields only gave a limited indication of the severity of the inflicted damage. Production of correlated breaks on the chromatin loop structures by single particle-track traversals may explain the deviations observed between experimental data and the predictions of the random breakage paradigm.     

Comparison of cytogenetic damage in cultured cells from cobalt-60 gamma-radiation and the Auger emitter zinc-65

Purpose : To assess the ability of the Auger-emitting nuclide, zinc-65 (65 Zn), relative to γ-irradiation, to cause chromosomal aberrations in cultured rat prostate cells. Materials and methods : Rat prostate adenocarcinoma cells in culture were exposed to doses of 1, 2, 3 or 5 Gy of external gamma-irradiation for 24h or incubated with 0.7, 1.5, 1.8 or 2.8MBq of 65 Zn for 24h. The uptake by and clearance from cells of 65Zn was measured. Metaphase spreads prepared from washed cells were scored for chromatid- and chromosome-type aberrations. Results : Following exposure to 65 Zn or γ-irradiation, chromatidtype damage was more commonly observed than chromosometype aberrations. The relationship between induced chromatid damage and gamma dose (to 3 Gy) was best fitted by a secondorder polynomial function, while the activity-response relationship for chromatid damage caused by 65 Zn appeared to be best fitted by a straight line. Measurements of the uptake of 65 Zn by cells showed that average concentrations within cells were about 100 times the concentration in the culture medium. Assuming uniform distribution of 65 Zn within cells, with 36% in the nucleus, the dose was estimated as 0.70 Gy per MBq added 65 Zn, with Auger electrons contributing most (93%) of the dose. Assuming that 20% of cellular zinc was localized in the nucleus, based on previous measurements, the dose to the nucleus was calculated as 0.44Gy per MBq added 65 Zn. RBE values for chromatid damage induced by 65 Zn compared to gamma-radiation range from about 1 to 3 based on a uniform dose throughout the cell and from about 2 to 5 based on 20% of 65 Zn in the cell nucleus. Conclusion : The observed radiotoxicity of 65 Zn is consistent with its behaviour as an Auger-emitting radionuclide that is localized to some extent in the nucleus.     

Evidence for an adaptive response to radiation damage in plant cells conditioned with X-rays or incorporated tritium

Allium cepa root-tip cells were first exposed to low 'conditioning' doses of ionizing radiation: to X-rays (0.06 or 0.26 Gy) or to incorporated tritium (1.8 x 10(4) or 7.2 x 10(4) Bq/ml; specific activity: 740.0 GBq/mmol) and subsequently given a 'challenge' dose of 1.5 Gy of X-rays. A reduction in X-ray-induced chromosomal damage was brought about by prior exposure to 0.26 Gy of X-rays, while cells receiving the lower conditioning dose (0.06 Gy of X-rays) did not show any significant reduction. In cells grown in the presence of [3H]TdR on the other hand, the adaptive response was evident after both doses given. The results are essentially in agreement with those published by Wolff's group for human lymphocytes in showing that plant cells in vivo can become 'adapted' by exposure to low-level irradiation so that they become more resistant to the clastogenic effects of X-rays delivered subsequently.     

Radioprotection mediated by the haemopoietic stimulation conferred by AM5: a protein-associated polysaccharide.

The haemopoietic and radioprotective effects of a protein-associated polysaccharide named AM5, have been studied following i.v. injection in mice. A dose-related accumulation of the splenic granulocyte-macrophage colony-forming units (CFU-GM) and colony-forming units in the spleen (CFU-S) was observed in mice treated with doses ranging from 0.1 to 0.4 mg/kg of AM5. The accumulation of splenic CFU-S, CFU-GM and BFU-e (erythroid burst-forming units) was always maximal 5 days after treatment with 0.4 mg/kg of AM5, with increases over control values between 300% and 500%. When the number of haemopoietic progenitors was quantified in the bone marrow, only slight increases of CFU-S were obtained, corresponding to the administration of low doses of AM5 (0.1 mg/kg). However, significant increases of circulating CFU-S were observed following administration of higher doses of AM5, suggesting a mobilization of haemopoietic progenitors from this organ. A faster recovery of spleen CFU-GM was observed in mice treated with 0.4 mg/kg of AM5 3 days or 1 day prior to a sublethal irradiation, and at this later time AM5 produced a significant survival enhancement from 10% to 90% in mice irradiated with 7.6 Gy X-rays. This effect was correlated with an increase in the nadir of leucocytes, characteristic of the radiation syndrome.     

Bone marrow from Balb/c mice radiocontaminated with 241Am in utero shows a deficient in vitro haemopoiesis

Radiation damage from 241Am to bone marrow cells was manifest in long-term bone marrow cultures (LTC) from offspring of mice radiocontaminated at the 14th day of gestation (119, 479, 803, 1754 kBq 241Am/kg). Offspring were reared by their own contaminated mother for 3 weeks postnatal. LTC from these offspring were less able to support in vitro CFC proliferation than control LTC from non-contaminated offspring. This radiation damage persisted 71 weeks after radiocontamination in utero. Using this in vitro culture system, damage was observed at lower doses if 241Am contamination occurred at foetal than at adult ages. Radiation damage was observed only using LTC, while the haemopoietic stem cell concentration (CFU-S, in vitro CFC) and the stromal stem cell concentration (CFU-F) from marrow in situ were not impaired after 241Am radiocontamination in utero. After culturing LTC in 25 per cent FCS and recharging the stromal adherent layer with bone marrow cell suspensions originating either from control offspring or from offspring contaminated with 241Am in utero, some evidence was found that the proliferation capacity of the haemopoietic cells was diminished. However, the nature of effects on the stromal elements is currently somewhat equivocal. Following in utero contamination the stromal adherent cells appeared to support better the production of in vitro CFC.     

Exposure of human osteosarcoma and bone marrow cells to tumour-targeted α-particles and γ-irradiation: analysis of cell survival and microdosimetry

Purpose : This study was designed to compare the cytotoxic effects of an α -emitting radioimmunoconjugate, which binds to osteosarcoma but not to bone marrow cells, with those of external γ-irradiation. Materials and methods : The human osteosarcoma cell line, OHSs1, and mononuclear cells from bone marrow (BM) harvested from healthy donors, were used for these experiments. Cells in suspension were added to various activity concentrations of the anti-osteosarcoma monoclonal antibody TP-3 radiolabelled with 211 At. Following incubation for 1 h, unbound radioactivity was washed off and cell survival was determined from clonogenic assays. Microdosimetry was calculated based on binding and retention kinetics of 211 At to the cells, as well as cellular and nuclear diameters. For comparison, cell suspensions were irradiated with a single dose of 60 Co γ-rays. Results : 211 At-labelled TP-3 showed heterogeneous binding to OHS-s1 cells, with a considerable variation among experiments. About 78% of the initially bound 211 At decayed while associated with the OHS-s1 cells. D 0 values estimated by microdosimetry were 0.33 (0.22-0.48, range) Gy and 1.18 (0.89-1.89) Gy for OHS-s1 and BM cells, respectively, whereas D0 values after external beam irradiation were 0.86 ±0.07 Gy and 1.71 ±0.22 Gy. The relative biological effectiveness (RBE) of 211 At-labelled TP-3 at 37% survival was 3.43 for OHS-s1 and 1.55 for BM. Conclusions : High-LET targeted α -particle exposure killed osteosarcoma cells more effectively than bone marrow cells, although heterogeneous antigen expression among these tumour cells limited the magnitude of this effect.     

Effect of tritiated water on female germ cells: mouse oocyte killing and RBE

The relative biological effectiveness (RBE) of tritiated water (HTO) was investigated using mouse immature oocytes. Juvenile mice, having immature oocytes that are highly sensitive to radiation killing, were exposed to HTO, 137Cs gamma rays, 60Co gamma rays, or 252Cf fission neutrons. The 137Cs gamma rays were used to simulate the changing dose rate (but not the radiation quality) received from HTO (see section 2). On the 14th day after birth, female ICR strain mice were injected once in the abdominal cavity with HTO at levels of 1.70, 3.40, 6.81, or 10.21 MBq/10g body weight, and their ovaries were removed 2 weeks after the injection. (The cumulative doses are equivalent to 0.039, 0.077, 0.159 and 0.246 Gy, respectively.) The survival rate of oocytes was determined by light microscopy inspection of serial sections, and the results of the different exposures were compared. The number of surviving oocytes decreased exponentially with increasing dose of HTO or 137Cs, and RBEs of HTO compared to 137Cs gamma rays ranged from 1.1 to 3.5. The relative effectiveness of the different types of radiations was compared, and the results of the comparison, in order of increasing effectiveness, was 137Cs, 60Co, HTO, and 252Cf. The RBE of 252Cf compared to 60Co gamma rays ranged from 1.6 to 3.5.     

Tumorigenic target cell regions in bone marrow studied by localized dosimetry of 239Pu, 241Am and 233U in the mouse femur

PURPOSE: To study the temporal change in microdistribution of plutonium-239, americium-241 and uranium-233 in the mouse distal femur and to compare and combine calculated radiation doses with those obtained previously for the femoral shaft. Also, to relate doses to relative risks of osteosarcoma and acute myeloid leukaemia. MATERIALS AND METHODS: Computer-based image analysis of neutron-induced and alpha-track autoradiographs of sections of mouse femora was used to quantify the microdistribution of (239)Pu, (241)Am and (233)U from 1 to 448 days after intraperitoneal injection. Localized dose-rates and cumulative doses over this period were calculated for different regions of the marrow spaces in trabecular bone. The results were then combined with previous data for doses to the cortical marrow of the femoral shaft. A morphometric analysis of the distal femur was carried out. RESULTS: Initial deposition on endosteal surfaces and dose-rates near to the trabecular surfaces at 1 day were two to four times greater than corresponding results for cortical bone. Burial was most rapid for (233)U, about twice the rate in cortical bone. As in cortical bone, subsequent uptake into the marrow was seen for (239)Pu and (241)Am but not (233)U. Cumulative doses to 448 days for different regions of trabecular marrow were greater than corresponding values for cortical marrow for each radionuclide. Combined doses reflected the greater overall volume of cortical marrow. CONCLUSIONS: Cumulative radiation doses to the 10 microm thick band of marrow adjacent to all endosteal surfaces were in the ratio of approximately 7:3:1 for (239)Pu:(241)Am:(233)U. This ratio is not inconsistent with observed incidences of osteosarcoma induction by the three nuclides. Analysis of doses to different depths of marrow, however, showed that although ratios were probably not significantly different to that for a 10 microm depth, better correlations with osteosarcomagenic risk were obtained with 20-40 microm depths. For acute myeloid leukaemia, the closest relationship between relative risk and doses was obtained by considering only the central 5-10% of marrow, which gave a dose ratio of approximately 12:11:1 for (239)Pu:(241)Am:(233)U respectively.     

Induction of chromosomal aberrations and sister chromatid exchanges by alpha particles in density-inhibited cultures of mouse 10T1/2 and 3T3 cells

We examined the dose-response relationships for the induction of cell killing, chromosomal aberrations and sister chromatid exchanges (SCE) by 220 kV X-rays and 5.3 MeV alpha particles from a 238Pu source. The cells were irradiated in density-inhibited, confluent cultures. The D0 values for the X-ray and alpha particle survival curves were 1.7 Gy and 0.7 Gy, and the extrapolation numbers 2.5 and 1.0, respectively, for mouse 3T3 cells. Chromosomal aberrations increased linearly with dose for alpha-radiation and roughly with the square of dose for X-rays in 3T3 cells. At 37 per cent survival, 1.0 chromosomal aberration per cell was induced by X-rays and 1.7 per cell by alpha-radiation, but the fraction of cells without aberrations was similar. In confluent holding recovery experiments there was a 50 per cent reduction in X-ray-induced aberrations during the first 4 h of confluent holding. No decline in alpha-induced aberrations was observed with holding times up to 24 h. The dose-response relationship for the induction of SCE by X-rays increased linearly with doses up to 100 cGy in both 3T3 and 10T1/2 cells, then declined, reaching nearly background levels after 400 cGy. The induction of SCE increased rapidly in these cell lines with doses of 2.5-5.0 cGy of alpha-radiation, then declined. The relative biological effectiveness (RBE) was 15-25 for the induction of SCE by low doses (2.5-5.0 cGy) of alpha particles.     

Microdistribution and localized dosimetry of the alpha-emitting radionuclides 239Pu, 241Am and 233U in mouse femoral shaft

PURPOSE: To analyse the temporal change in microdistribution of 239Pu, 241Am and 233U in mouse femur and to compare the calculated radiation doses with regions of the bone marrow thought to contain target cells for osteosarcoma and leukaemia with relative risk for those diseases. MATERIALS AND METHODS: Neutron-induced and alpha-track autoradiographs were prepared from femora of the CBA/H mouse that had been injected with 40 kBq kg(-1) radionuclide between 1 and 448 days previously. Computer-based image analysis of the autoradiographs was performed and dosimetric methods applied to obtain radiation dose-rates to different regions of the marrow cavity. RESULTS: Initially each radionuclide deposited on endosteal and periosteal bone surfaces; 241Am was additionally deposited on vascular canal surfaces. Redistribution resulted in 233U being incorporated into bone, while 239Pu and 241Am showed transfer into both bone volume and marrow. Accumulation in the central marrow peaked at 112-224 days post-injection, but subsequently was cleared by 448 days. Cumulative doses to both osteosarcomagenic and myeloid leukaemogenic target cell regions showed the trend 239Pu > 241Am > 233U. CONCLUSIONS: Calculation of cumulative doses to a 10-microm layer of marrow adjacent to bone surfaces appears to be a suitable predictor for risk of osteosarcoma. Risks of myeloid leukaemia in the mouse are better predicted by considering the central marrow as the target region rather than average dose to all marrow.     

Induction of osteosarcoma and acute myeloid leukaemia in CBA/H mice by the alpha-emitting nuclides, uranium-233, plutonium-239 and amercium-241

PURPOSE: To compare tumour induction in CBA/H mice, principally osteosarcoma and acute myeloid leukaemia, resulting from exposure to the alpha-emitting nuclides, uranium-233, plutonium-239 and americium-241, and to relate differences between the three nuclides to the pattern of dose delivery within tissues. MATERIALS AND METHODS: Each nuclide was administered intraperitoneally in citrate solution to three groups of adult male CBA/H mice at levels of activity which gave estimated life-time average skeletal doses of about 0.25-0.3 Gy, 0.5-1 Gy and 1-2 Gy. Animals were carefully monitored and sacrificed as soon as they showed signs of ill health; tumours were identified by standard histopathological techniques. RESULTS: Statistical modelling by Cox regression showed that, considering all three nuclides together, there was a highly significant increase in risk of death from osteosarcoma or myeloid leukaemia with increasing dose rate. For osteosarcoma, the effect was significantly greater for 239Pu than 241Am, while separate analysis for 233U showed no significant increase with increasing dose rate. For example, the increase in relative risk of death from osteosarcoma for an increase in life-time average dose rate to bone of 1 mGyd(-1) was 4.2 (2.7-6.5) for 239Pu, 2.3 (1.4-3.4) for 241Am and 1.1 (0.4-3.1) for 233U. For myeloid leukaemia, there was no significant difference between 239Pu and 241Am in the effect of dose rate. The increase in relative risk from myeloid leukaemia for an increase in average dose rate of 1 mGyd(-1) was 1.8 (1.1-2.8) for 239Pu, 2.0 (1.4-2.9) for 241Am and 1.5 (0.8-2.7) for 233U. Significant increases in renal and hepatic carcinomas were also recorded in animals exposed to 233U and 241Am, respectively. Studies of the distribution of the nuclides within the skeleton, published separately, have shown differences in their retention in individual bones and within bone. The proportions of decays occurring near to endosteal bone surfaces and throughout bone marrow were in the order: 239Pu> 241Am>233U. CONCLUSIONS: For osteosarcoma, the relative effectiveness of the nuclides in terms of average bone dose, in the order 239Pu>241Am>233U, is consistent with the proportion of dose delivered near to endosteal surfaces. For myeloid leukaemia, the greater effectiveness of 239Pu and 241Am than 233U is consistent with their accumulation in marrow.     

The relative biological effectiveness of 60Co gamma-rays, 55 kVp X-rays, 250 kVp X-rays, and 11 MeV electrons at low doses.

The relative biological effectiveness (RBE) of selected low-LET radiation modalities (55 kVp X-rays, 250 kVp X-rays, 60Co gamma-rays, and 11 MeV electrons) was investigated for survival of two cell lines (V79 and CHO). Detailed measurements were made in the low (0 to 3 Gy) dose range using an image cytometry device to accurately determine the number of cells assayed at each dose point. Data were also collected in the high dose range (0 to 10 Gy) using conventional counting and plating techniques. RBE values (+/- 1 SE) varied from 1.0 +/- 0.07 (V79 cells) and 1.2 +/- 0.05 (CHO cells) at high doses to 1.3 +/- 0.07 (V79) and 1.4 +/- 0.1 (CHO) at low doses for 55 kVp X-rays, from 1.1 +/- 0.05 (V79) and 1.1 +/- 0.04 (CHO) at high doses to 1.1 +/- 0.06 (V79) and 1.2 +/- 0.2 (CHO) at low doses for 250 kVp X-rays, and from 1.1 +/- 0.08 (V79) and 1.0 +/- 0.04 (CHO) at high doses to 1.0 +/- 0.06 (V79) and 0.9 +/- 0.1 (CHO) at low doses for 11 MeV electrons. Only the low and high dose RBEs for 55 kVp X-rays relative to 60Co gamma-rays were significantly different.