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

Purpose : To assess in utero sensitivity to x-rays, α -emissions from plutonium-239 and β -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 α -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 α -irradiation since the overall estimated in utero α -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 α -particles from 239 Pu than X-rays or β -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-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.

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.     

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.     

High radiosensitivity of the mineralization capacity of adult murine bone marrow in vitro to continuous alpha-irradiation compared to acute X-irradiation.

Adult BALB/c mice, injected with osteosarcomogenic amounts of 241Am (between 40 and 500 Bq/g mouse) showed an impaired mineralization capacity of their femoral bone marrow. This effect persisted until at least 1 year after 241Am injection and was expressed after incubation of bone marrow cells in vitro in conditions allowing osteogenic differentiation. The mineralization capacity of marrow in vitro was evaluated by measurement of 85Sr uptake from the tissue culture medium. Two osteogenic assays were used: in marrow cultured as an intact organ (marrow organ cultures), reduced mineralization was observed in mice given 149 Bq 241Am/g mouse or more (skeletal dose rate of 25 mGy/day), in stromal marrow cells cultured from adherent cell layers and subsequently brought into a three-dimensional (3D) mineralizing condition (stromal 3D cultures), reduced 85Sr uptake was observed from the lowest dose level tested (42 Bq 241Am/g mouse, skeletal dose rate of 7 mGy/day). Taking into account that only a fraction of the skeletal alpha-dose reached the marrow of the femoral diaphyses, marrow organ cultures and stromal 3D cultures exhibited high radiosensitivity to alpha-irradiation in vivo. However, after acute X-irradiation of marrow in vivo or in vitro prior to initiation of the marrow organ cultures, X-ray doses of 4 Gy or higher were needed to significantly impair the mineralization capacity of marrow organ cultures in vitro. Our data demonstrated that the osteogenic cells from the bone marrow are subjected to long-term damage after low doses of continuous alpha-irradiation in vivo.     

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.     

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.     

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.     

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.     

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.     

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.     

Radiation dosimetry results and safety correlations from 90Y-ibritumomab tiuxetan radioimmunotherapy for relapsed or refractory non-Hodgkin's lymphoma: combined data from 4 clinical trials.

Ibritumomab tiuxetan is an anti-CD20 murine IgG1 kappa monoclonal antibody (ibritumomab) conjugated to the linker-chelator tiuxetan, which securely chelates (111)In for imaging or dosimetry and (90)Y for radioimmunotherapy (RIT). Dosimetry and pharmacokinetic data from 4 clinical trials of (90)Y-ibritumomab tiuxetan RIT for relapsed or refractory B-cell non-Hodgkin's lymphoma (NHL) were combined and assessed for correlations with toxicity data. METHODS: Data from 179 patients were available for analysis. Common eligibility criteria included <25% bone marrow involvement by NHL, no prior myeloablative therapy, and no prior RIT. The baseline platelet count was required to be > or = 100,000 cells/mm(3) for the reduced (90)Y-ibritumomab tiuxetan administered dose (7.4-11 MBq/kg [0.2-0.3 mCi/kg]) or > or = 150,000 cells/mm(3) for the standard (90)Y-ibritumomab tiuxetan administered dose (15 MBq/kg [0.4 mCi/kg]). Patients were given a tracer administered dose of 185 MBq (5 mCi) (111)In-ibritumomab tiuxetan on day 0, evaluated with dosimetry, and then a therapeutic administered dose of 7.4-15 MBq/kg (0.2-0.4 mCi/kg) (90)Y-ibritumomab tiuxetan on day 7. Both ibritumomab tiuxetan administered doses were preceded by an infusion of 250 mg/m(2) rituximab to clear peripheral B-cells and improve ibritumomab tiuxetan biodistribution. Residence times for (90)Y in blood and major organs were estimated from (111)In biodistribution, and the MIRDOSE3 computer software program was used, with modifications to account for patient-specific organ masses, to calculate radiation absorbed doses to organs and red marrow. RESULTS: Median radiation absorbed doses for (90)Y were 7.42 Gy to spleen, 4.50 Gy to liver, 2.11 Gy to lung, 0.23 Gy to kidney, 0.62 Gy (blood-derived method) and 0.97 Gy (sacral image-derived method) to red marrow, and 0.57 Gy to total body. The median effective blood half-life was 27 h, and the area under the curve (AUC) was 25 h. No patient failed to meet protocol-defined dosimetry safety criteria and all patients were eligible for treatment. Observed toxicity was primarily hematologic, transient, and reversible. Hematologic toxicity did not correlate with estimates of red marrow radiation absorbed dose, total-body radiation absorbed dose, blood effective half-life, or blood AUC. CONCLUSION: Relapsed or refractory NHL in patients with adequate bone marrow reserve and <25% bone marrow involvement by NHL can be treated safely with (90)Y-ibritumomab tiuxetan RIT on the basis of a fixed, weight-adjusted dosing schedule. Dosimetry and pharmacokinetic results do not correlate with toxicity.     

Chromosome damage induced by high-LET alpha-particles in plateau-phase C3H 10T1/2 cells.

Chromosome aberrations induced by X-rays and alpha-particles (LET = 177 keV/microns) were observed at the first mitosis in C3H 10T1/2 cells released from density-inhibited cultures. X-radiation induced more chromosome exchanges than breaks (71% vs 27% of total aberrations), while a predominance of breaks (63%) was observed after alpha-irradiation. A linear-quadratic dose-response relationship was obtained for X-rays, while that for alpha-particles was linear. The RBE values for total aberration induction (ranging from 5.1 at low doses to 4.4 at high doses) were very similar to the RBE for cell killing (from 5.2 to 4.3). The RBE for dicentric induction (approximately 2) was much lower than the RBE for the induction of both breaks (from 7 to 6) and interstitial deletions (from 9 to 7). This behaviour supports the hypothesis that chromosome deletions play a major role in the malignant transformation of 10T1/2 cells. A high correlation between cell killing and number of acentric fragments per cell was found. The number of acentrics/cell at the mean lethal dose was about 1.4. This number was reduced to 1.0 when asymmetrical interchanges, which generally result in very small deletions, were subtracted from acentrics. It could be hypothesized that very small deletions could not impair cell survival. However, an alternative hypothesis related to the aneuploid state of C3H 10T1/2 cells can be formulated. Robertsonian translocations were also observed at the first mitosis. The dose-response curve of these translocations appears to be very similar to the dose-response curve for induction of sister chromatid exchanges (observed at the second mitosis) reported by other authors studying the same cell line. This similarity could indicate a general mechanism of action of radiation on the process of recombination of genetic material.     

Inability of Dimethyl Sulphoxide to Protect Mouse Testis against the Effect of X-radiation

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 40kBqkg 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 239 Pu> 241 Am> 233 U. Conclusions: Calculation of cumulative doses to a 10-mum 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.     

Myelotoxicity and RBE of 211At-conjugated monoclonal antibodies compared with 99mTc-conjugated monoclonal antibodies and 60Co irradiation in nude mice.

The rationale of this study was to determine the myelotoxicity in nude mice of the alpha-emitter 211At conjugated to monoclonal antibodies (mAbs) and to compare the effect with an electron emitter, (99m)Tc, and external irradiation from a 60Co source, for estimation of the relative biological effectiveness (RBE). METHODS: 211At and (99m)Tc were conjugated to the IgG1 mAbs MX35 and 88BV59. Nude female BALB/c mice, 8- to 12-wk old, were injected intraperitoneally or intravenously. The biodistribution was determined 3, 6, and 18 h after injection. The bone-to-blood and bone marrow-to-blood activity concentration ratios (BBLR and BMBLR, respectively) were determined for simultaneously injected 211At- and (99m)Tc-mAbs. Bone marrow samples were taken from the femur. For each mouse, the whole-body retention was measured as well as the blood activity by repeated blood samples from the tail vein (0), 1, 3, 6, 12, and 18 h after injection. External-beam irradiation from a 60Co source was also performed at 3 different dose levels. White blood cell (WBC) counts, red blood cell counts, platelet counts, and hemoglobin were determined for each mouse initially and on days 1, 4, 5, 7, 15, 22, and 27 after injection. The calculations of the absorbed dose to the bone marrow were based on the BBLR, BMBLR, the cumulated activities, and the absorbed fractions. The absorbed fractions, phi, for alpha-particles and electrons in the bone marrow were calculated using Monte Carlo simulations based on a bone marrow dosimetry model. RESULTS: The BMBLR was 0.58 +/- 0.06 and 0.56 +/- 0.06 for the 211At- and (99m)Tc-mAbs, respectively. No significant variation in BMBLR with time was found. The absorbed fractions for alpha-particles and electrons in the bone marrow were 0.88 and 0.75, respectively. The mean absorbed fractions of the photons from (99m)Tc were 0.033 and 0.52 for 140 and 18.3 keV, respectively. When different amounts of 211At- and (99m)Tc-mAbs (0.09-1.3 and 250-1,300 MBq, respectively) were administered intraperitoneally or intravenously, corresponding to absorbed doses to the bone marrow of 0.01-0.60 and 0.39-1.92 Gy, respectively, the WBC counts was suppressed by 1%-90% and 23%-89%, respectively. When external-beam irradiation with a 60Co source was performed to absorbed doses of 1.4, 1.9, and 2.4 Gy, the WBC counts was suppressed by 47%-90%. These results indicate a myelotoxic in vivo RBE of 3.4 +/- 0.6 for alpha-particles compared with (99m)Tc and 5.0 +/- 0.9 compared with 60Co irradiation. CONCLUSION: The effect on the WBC counts from bone marrow irradiation with 211At-mAbs indicates an in vivo RBE of 3.4 +/- 0.6 in comparison with (99m)Tc-mAbs. The RBE value compared with external irradiation is 5.0 +/- 0.9.     

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.     

Evaluation of the cytogenetic damage and progenitor cell survival in foetal liver of mice exposed to gamma radiation during the early foetal period

PURPOSE: To investigate the haemopoietic response to low dose gamma irradiation at the early foetal period when the liver is the major haemopoietic organ. MATERIALS AND METHODS: Pregnant Swiss albino mice were exposed to 0.1-1.5 Gy of gamma radiation on the 14th day of gestation. Twenty-four hours (15 day post conception (p.c.)) and 72 h (17 day p.c.) after exposure, the foetuses were dissected out, weighed, and liver weight and mean cellularity were determined. Cytogenetic damage in liver cells was assessed by chromosome aberration analysis and micronucleus (MN) count. The haemopoietic progenitor cell survival at 24 h and 72 h after exposure was measured by exogenous spleen colony assay on day 8 (CFU-S8) and day 12 (CFU-S12) after intravenous injection of the foetal liver cells into adult bone marrow-ablated recipient mice. RESULTS: The foetal body weight at 24 h after exposure showed a significant reduction at doses of 0.5 Gy and above, while the 72 h body weight was significantly lower than control from 0.3 Gy onwards. Liver weight showed a similar reduction for doses from 0.25 to 1.5 Gy at both the post-irradiation observation times. However, when liver weight/body weight ratios were compared, there was no significant difference between the irradiated and control values. Total liver cellularity at 24 h and 72 h after exposure showed a dose-dependent decrease, with significant depletion from control at 0.25 Gy and above. When donor cells were taken at 24 h after exposure (15 day p.c.) the CFU-S8 showed a significant decrease only at 1.0 and 1.5 Gy, while the CFU-S12 suffered such a depletion at 0.25-1.5 Gy. For donor cells recovered at 72 h after exposure, both CFU-S8 and CFU-S12 decreased linear-quadratically with radiation dose and were significantly lower than control at 0.25 Gy. A significant increase in the percent aberrant metaphases and micronucleus counts was seen at 0.1 Gy and 0.15 Gy, respectively, and increased linear-quadratically with radiation dose. CONCLUSIONS: The results demonstrate that the liver, which is the major haemopoietic organ at the early foetal period, is highly sensitive to radiation damage from maternal irradiation. At low doses, the lethal effect on the haemopoietic stem cells appears to develop more slowly than at higher doses.     

Prospective 153Sm-EDTMP therapy dosimetry by whole-body scintigraphy.

Samarium-153 ethylenediaminetetramethylene phosphonic acid (153Sm-EDTMP) effectively palliates painful bony metastases, but the standard recommended administered activity of 38 MBq.kg-1 may lead to significant myelotoxicity. Prospective individual dosimetry by urine collection and counting allow the bone marrow radiation dose to be limited to 2 Gy. Our novel whole-body scintigraphic method for prospective dosimetry was compared with the 5 h urine collection technique in 10 patients with bone metastases. Anterior and posterior whole-body images were obtained using identical acquisition parameters 10 min and 5 h after the intravenous injection of 740 MBq 153Sm-EDTMP. Total counts in each imaging study were corrected for background activity and time of injection and the bone activity at 5 h was determined. Bone activity was also calculated from a complete urine collection over 5 h, and these two values were compared. MIRD formulae were applied to calculate the radiation absorbed dose to the bone marrow from the injected activity. The total activity delivering a dose of 2 Gy to the bone marrow was then determined and constituted the amount given for therapy. Values for bone activity determined by imaging and by urine counting were concordant in all patients (correlation coefficient = 0.98). The total administered activity of 153Sm-EDTMP predicted on a 2 Gy bone marrow dose varied between 35 and 63% of the standard recommended regimen of 37 MBq.kg-1 and pain relief was experienced by eight of the ten patients. Administration of 153Sm-EDTMP according to the supplier's recommendations would have delivered bone marrow doses of 3.27-5.90 Gy in our patients, doses at which myelotoxicity would have been anticipated.     

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.