Partial-body Irradiation Research Articles

Chromosomal biodosimetry by unfolding a mixed Poisson distribution: a generalized model

Purpose : The current chromosomal biodosimetry system is practically limited to the estimation of equivalent whole-body dose in the low or moderate dose range. To circumvent this problem, a new dosimetry system was developed which was effective over a wide dose range and dose gradient. Materials and methods : In order to establish a quantitative formalism of a comprehensive dose-response kinetics, chromosome aberration frequencies were studied in human peripheral blood lymphocytes irradiated in vitro with γ-rays in a dose range of 0.01-50Gy. Using the dose-yield relationship thus established, a new model of biodosimetry was developed which involved unfolding the chromosome aberration distribution into a mixed Poisson distribution and thence into a dose-distribution profile. The model was then tested with chromosome aberration data in lymphocytes irradiated in vitro, simulated partial body irradiation, accidental radiation exposure, therapeutic local irradiation and protracted exposure by internal deposit of Thorotrast. Results : The dose-yield relations over a wide dose range fit satisfactorily a multiparametric dose-response curve, which included the first approximation kinetics of linear-quadratic dose-response and its distortion by mutual interference among multiple breaks on a chromosome arm. The unfolding strategy using these dose-response kinetics was successfully applied to the various types of radiation exposures; the reconstructed dose profile showing a sharp unimodal peak for moderate or high doses of γ-rays in vitro irradiation, broadening for high-linear energy transfer radiation, discrimination of doses in the mixed culture of irradiated and unirradiated blood, and reasonable dose distribution for the in vivo exposures. Conclusion : A novel biodosimetry system was developed. The system is innovative in that it provides information not only on the macroscopic dose inhomogeneity, but also on the microscopic spectrum of doses stemming from the variability of energy transfer by charged particles as well as the multiple ionization events to which the target cell nucleus is exposed.

Relationship between oocyte apoptosis and ovarian tumours induced by high and low LET radiations in mice

Purpose : To investigate the biological effectiveness of neutrons at the energy below 1 MeV on apoptosis and carcinogenesis in the mouse ovary. Materials and methods : Female mice were exposed to 1.0 Gy monoenergetic neutrons (0.317, 0.525 and 1.026 MeV), 252 Cf fission neutron (2.13 MeV) or 137 Cs γ-rays at 7 days of age. Apoptosis of the oocyte and pregranulosa cells, and ovarian carcinogenesis were compared between the radiations. The efficiency of γ-rays for granulosa cell tumorigenesis was tested by transplantation of the irradiated ovaries into non-irradiated mice. Results : The cumulative apoptotic index of oocytes was 77.9%, 65.6% and 41.6% for the 0.525 MeV neutron, 2.13 MeV neutron and γ-rays, respectively. Follicles with apoptotic pregranulosa cells were 53.0%, 18.3% and 22.8% of cumulative index for the three groups. Tubular adenomas developed in the groups of monoenergetic neutrons (26.1%) and γ-ray (35.5%), whereas granulosa cell tumours developed only in the γ-ray groups (3.2% for 1.0 Gy and 15.6% for 3.0 Gy). Partial-body irradiation with 3 Gy γ-rays to the ovaries induced granulosa cell tumours with an incidence of 27.3%. Conclusion : Effectiveness of neutrons to cause apoptosis was higher for 0.525 MeV than for 2.13 MeV. The pregranulosa cell apoptosis occurred in an oocyte-prone manner. The higher effectiveness of neutrons than γ-rays to induce oocyte and pregranulosa cell apoptosis correlates with the inhibition of granulosa cell tumour development.

Chromosomal biodosimetry by unfolding a mixed Poisson distribution: a generalized model

Purpose : The current chromosomal biodosimetry system is practically limited to the estimation of equivalent whole-body dose in the low or moderate dose range. To circumvent this problem, a new dosimetry system was developed which was effective over a wide dose range and dose gradient. Materials and methods : In order to establish a quantitative formalism of a comprehensive dose-response kinetics, chromosome aberration frequencies were studied in human peripheral blood lymphocytes irradiated in vitro with γ-rays in a dose range of 0.01-50Gy. Using the dose-yield relationship thus established, a new model of biodosimetry was developed which involved unfolding the chromosome aberration distribution into a mixed Poisson distribution and thence into a dose-distribution profile. The model was then tested with chromosome aberration data in lymphocytes irradiated in vitro, simulated partial body irradiation, accidental radiation exposure, therapeutic local irradiation and protracted exposure by internal deposit of Thorotrast. Results : The dose-yield relations over a wide dose range fit satisfactorily a multiparametric dose-response curve, which included the first approximation kinetics of linear-quadratic dose-response and its distortion by mutual interference among multiple breaks on a chromosome arm. The unfolding strategy using these dose-response kinetics was successfully applied to the various types of radiation exposures; the reconstructed dose profile showing a sharp unimodal peak for moderate or high doses of γ-rays in vitro irradiation, broadening for high-linear energy transfer radiation, discrimination of doses in the mixed culture of irradiated and unirradiated blood, and reasonable dose distribution for the in vivo exposures. Conclusion : A novel biodosimetry system was developed. The system is innovative in that it provides information not only on the macroscopic dose inhomogeneity, but also on the microscopic spectrum of doses stemming from the variability of energy transfer by charged particles as well as the multiple ionization events to which the target cell nucleus is exposed.

Structure and function of bone marrow hemopoiesis: mechanisms of response to ionizing radiation exposure.

It is the purpose of this presentation to review the unique structure and function of bone marrow anchored hematopoiesis in their significance for its response mechanisms to an exposure to ionizing radiation. The ultimate objective of bone marrow hematopoiesis is to maintain in the peripheral blood a constant level of the different blood cell types (erythrocytes, granulocytes, platelets, lymphocytes, etc.). All of them have their particular turnover kinetics (such as granulocytes 120 x 10(9)/d, erythrocytes 200 x 10(9)/d or thrombocytes 150 x 10(9)/d), are semi-autonomous in their steady state regulatory mechanisms and dependent on a life-long supply of mature cells from a stem cell pool with unlimited replicative and pluripotent differentiative potential. The present knowledge of hematopoietic cellular renewal is the result of years of basic experimental and clinical studies using radionuclides in various metabolic forms including (59)Fe, (32)P (DF (32)P), (51)Cr, (131)I, (60)Co, (3)H ((3)HTdR) and (14)C ((14)CTdR). To understand the physiology but in particular the radiation-pathophysiology, it is essential to recognize in detail the infrastructure of the bone marrow as a distinct unit. Indispensable for a life-long cell production is the capsule of the marrow - the bone cortex -, the arterial supply of blood connected to the sinusoidal microvascular architecture with its sinusoids contorti and recti as well as the central (cell collecting) sinusoids. It is further of importance to recognize the significance of nerval regulation of blood flow, characterized by myelinated and unmyelinated nerve fibers. The type of unique lining cells of the sinusoids is the prerequisite for the cell traffic between the hemopoietic parenchyma and the blood. This in turn cannot be achieved without an alternative opening and closing of the sinusoidal segments which - in turn - requires a rigid long capsule to assure an - in toto - constant volume of each bone marrow unit. If a bone marrow unit is exposed to ionizing radiation, a perturbance of the balance between cellular growth pressure and blood flow dynamics can be observed, resulting in a special type of bone marrow hemorrhage and an "excess cell loss" that may result in an non-thrombopenic exhaustion of the stem cell pool. Of great importance is the question as to the mechanisms that allow the bone marrow hemopoiesis to act as one cell renewal system although the bone marrow units are distributed throughout more than 100 bone marrow areas or units in the skeleton. The observation that "the bone marrow" acts and reacts as "one organ" is due to the regulatory mechanisms: the humeral factors (such as erythropoietins, granulopoietins, thrombopoietins etc.), the nerval factors (central nervous regulation) and cellular factors (continuous migration of stem cells through the blood to assure a sufficient stem cell pool size in each bone marrow "sub-unit"). It should be recalled that the bone marrow functions as a physiological chimera and becomes established by the hematogeneic seeding of stem cells to a mesenchymal matrix during embryogenesis. The repopulation of the bone marrow after partial body irradiation, after strongly inhomogeneous radiation exposure or after total body exposure with stem cell transplantation can well be considered as a repetition of the embryogenesis of bone marrow hemopoiesis with the key element of stem cells migrating via the blood to stromal sites of the marrow prepared to accept stem cells to home and start their replication and differentiation if the micro-environmental quality permits. In summary, the radiation biology of bone marrow hemopoiesis requires a thorough understanding of the physiology and pathophysiology of structure, function and regulation not only of the process of cellular renewal but also of the intricate infrastructure.

Persistence of micronuclei in lymphocytes of cancer patients after radiotherapy.

To verify the applicability of the micronucleus (MN) yield in peripheral blood lymphocytes (PBLs) as a quantitative biodosimeter for monitoring in vivo ionizing radiation damage, we applied the cytokinesis-blocked micronucleus assay in PBLs of cancer patients treated with partial-body radiotherapy. Dosimetric information on these 13 patients represented a wide range in the number of fractions, cumulative tumor dose, total integral dose, and equivalent total-body absorbed dose. We found in PBLs of these patients that (1) the MN yield increased linearly with the equivalent total-body absorbed dose (r = 0.8, P = 0.002), (2) the distributions of the MN yields deviated significantly from Poisson, and (3) there was a general decline in MN yields with increasing length of follow-up, but with considerable variation between individuals. The average rate of decline was found to be linear and was correlated with the equivalent total-body absorbed dose (r = 0.7, P = 0.007). Further, at 19-75 months of follow-up time, seven patients showed higher MN yields than their respective levels before radiotherapy, indicating the persistence of radiation-induced residual cytogenetic damage. Our findings suggest that the MN yield in human PBLs offers a reliable acute and perhaps chronic biodosimeter for in vivo radiation dose estimation. After the completion of radiotherapy, the persistence of elevated MN yield in PBLs is a reflection of the surviving population of radiation-induced genetically aberrant cells.

Intercomparison of translocation and dicentric frequencies between laboratories in a follow-up of the radiological accident in Estonia

Purpose : To perform an interlaboratory comparison of FISH chromosome painting and to study the time-course of translocations and dicentrics in three accident victims exposed to radiation. Also, to use the data in the validation of the FISH technique as a retrospective dosimeter. Materials and methods : Twelve blood samples were collected during 4 years from three subjects exposed to radiation in an accident in Estonia in 1994 involving γ -radiation from a 137Cs source. Two of the subjects were exposed during approximately 7 h, both receiving a protracted dose of about 1 Gy and also localized exposure. The third subject received a protracted whole-body dose of 2.7Gy during 4 weeks as well as a short-term partialbody dose. Preparations from 48-h metaphase cultures were painted by the FISH technique using routine methods and probe cocktails in four laboratories. Samples from each subject were analysed in two different laboratories that used different combinations of whole chromosome probes. The PAINT nomenclature was applied when recording chromosome aberrations. Results : The intercomparison of FISH analysis data showed reasonable similarities between laboratories, the largest discrepancy being 21% in the frequency of two-way translocations in subject 3. Half-time calculations, based on combined data sets from two laboratories, showed that dicentrics decreased rapidly with half-times of approximately 2 years. In all cases, the initial dicentric yields were lower than the initial translocation yields. During the 4-year follow-up, the frequencies of all translocations in cells containing only simple rearrangements fell on average to about 65% of their initial value. Two-way translocations were slightly more persistent than all translocations. The average halftime was about 8 years for two-way translocations and around 6 years for all translocations. Cells containing complex rearrangements were few in number and they disappeared with time. In general, the inclusion of complex cells caused a more rapid fall in aberration yield. Conclusions : In general, the results imply that relatively consistent scoring data were obtained with different chromosome painting protocols. They also support the idea that the reduction of translocations with time is associated with partial-body irradiation.

Reciprocal translocations in patients with testicular seminoma before and after radiotherapy

Purpose: The evaluation of radiation-induced chromosomal translocations in peripheral lymphocytes using fluorescent in situ hybridization is a promising method for retrospective dosimetry after a radiation accident. We evaluated the genomic frequency of chromosomal translocations in patients with testicular seminoma who received adjuvant radiotherapy to the retroperitoneal lymph nodes, to evaluate the time–effect relationship of radiation-induced stable aberrations after partial body irradiation. Methods: In 13 patients, peripheral lymphocytes could be evaluated before radiotherapy and at several time points after radiotherapy. In 17 additional patients, lymphocyte samples were obtained after radiotherapy. Thirteen healthy men served as age-matched controls for the aberration frequency before radiotherapy. Fluorescent in situ hybridization was performed using whole chromosome probes against chromosomes No. 4, No. 6, and No. 7. Results: Nearly all patients displayed an increased spontaneous rate of genomic translocations ( F G ) before radiotherapy compared to age-matched, healthy men. The difference was significant in the paired ranks test ( p < 0.0001). After adjuvant radiotherapy, the F G increased 2- to 8-fold in individual patients. Within 20 months after radiotherapy, the F G returned to pretherapeutic levels. Conclusions: The frequency of genomic translocations after partial body irradiation is time dependent. A persistence of chromosomal aberrations, which is to be expected after total body irradiation, could not be observed. It is likely that the dose and the volume of the irradiated bone marrow are playing a role in the persistence of stable chromosomal aberrations. Patients with testicular seminoma displayed an increased frequency of spontaneous genomic translocations before the initiation of radiotherapy. This chromosomal instability might be related to the known increased rate of secondary cancers in this patient group.

Level of Flt3-ligand in plasma: a possible new bio-indicator for radiation-induced aplasia

Purpose : To follow plasma Flt3-ligand (FL) concentrations in irradiated animals in order to evaluate it as an indicator of bone marrow damage for the management of accidental radiation-induced aplasia. Materials and methods : Non-human primates were irradiated at doses ranging from 2 to 8 Gy, using whole- or partial-body irradiation. Plasma FL concentrations and blood cell counts were determined daily. Results : FL concentrations increased as early as day 2 after irradiation, whatever the irradiation dose. Increase in plasma FL concentration on day 5 post-irradiation was correlated with radiation dose and with the severity of radiation-induced aplasia. During the course of aplasia, FL concentrations in plasma were inversely correlated with neutrophil counts. A peak in FL concentration appeared before the neutrophil nadir, and the subsequent decrease in FL concentration was correlated with the recovery of blood-cell populations. Conclusions : Monitoring plasma FL concentration can be used as an indicator of radiation-induced marrow aplasia, and this may be of use in accidental irradiation situations.

Time-course of translocation and dicentric frequencies in a radiation accident case

Purpose : To assess the persistence of exchange aberrations measured by FISH chromosome painting after accidental radiation exposure. Materials and methods : Chromosome analyses were carried out in peripheral lymphocytes of a 13-year-old boy exposed to protracted low dose-rate whole-body and short-time partial-body irradiation from a radiation accident in Estonia in 1994. Up to November 1998, the frequencies of translocations and dicentrics were periodically measured using FISH chromosome painting of the target chromosomes 1, 4 and 12, with a simultaneous pancentromeric probe. Results : For the yields of dicentrics, an expected rapid temporal decline was found with a half-time of 14.2 ±1.9 months. The yields of reciprocal translocations also revealed a gradual but significant reduction with a half-time of 51.7 ±12.7 months. Conclusion : An unchanged temporal persistence of so-called stable translocations cannot be assumed. Any significant reduction of this aberration type with time obviously limits the application of FISH-based translocation measurements for reliable long-term biodosimetry after combined protracted whole-body and partial-body radiation exposure.

Image processing of medical infrared images for monitoring local conditions during radiotherapy

Radiation therapy (radiotherapy) is a valuable technique used in medicine for cancer treatment. It is a fact that many of the incidents and accidents involve only partial body irradiation and the extremities are the most frequently injured parts of the body. As it is still not general practice to use infrared (IR) thermographic imaging for the more precise diagnosis of local injuries, the availability of these techniques is very rarely mentioned in the publications. In this paper attention is drawn to what was introduced more than a decade ago, namely the use of IR thermographic procedures in diagnosing local radiation injuries. Further justification for introducing these techniques is that, in the relevant cases, the assessment of absorbed radiation dose through the widely known biological indicators or biological dosimetry assays is not always possible.

Follow-up analysis of translocation and dicentric frequencies, measured by FISH-chromosome painting in breast cancer patients after partial-body radiotherapy with little bone marrow exposure

Follow-up translocation and dicentric measurements in blood lymphocytes of five breast cancer patients were performed by FISH using painting probes for chromosomes 1, 4, and 12 simultaneously with a pancentromeric DNA probe, during 14 months after fractionated photon therapy affecting only small areas of the bone marrow (about 5%). The analysis of individual time-courses for translocations and dicentrics revealed a significant temporal decline of the yields with comparable half-times, both for these stable and unstable aberration types in two patients. In three patients, the aberration yields remained fairly unchanged during the observation period. Regarding retrospective biodosimetry for cases with partial-body exposures or large dose inhomogeneity, it follows that even FISH chromosome painting is limited in assessing initial doses correctly in terms of stable translocations.

Effect of blood storage on radiation-induced micronuclei in human lymphocytes

To evaluate the effect of blood storage on the yield of micronuclei (MN) in both irradiated (in vivo and ex vivo) and unirradiated peripheral blood lymphocytes (PBL), we applied the MN assay in cytokinesis-blocked (CB) PBL obtained from healthy subjects ( n=11), and from cancer patients ( n=10) who were undergoing fractionated partial-body radiotherapy (xRT). The heparinized blood samples were exposed to 137 Cs -irradiation (0 Gy or 2 Gy) immediately after blood collection and were stored upright in test tubes either at room temperature (22°C) or in the refrigerator (5°C). Duplicate whole blood cultures from each sample were set up at 0 h, 96 h, and 120 h after ex vivo irradiation. Giemsa (10%) stained slides were prepared from each culture. MN yield was determined per 1000 binucleated cells. As compared to that obtained from the corresponding fresh blood samples, we found that (1) the 22°C blood storage temperature did not affect MN yields in PBL of either healthy subjects or cancer patients up to 96 h, either with or without ex vivo irradiation; and (2) while blood samples were stored at 5°C, the MN yield increased significantly in PBL of healthy subjects (with or without ex vivo irradiation) at 120 h, and in cancer patients (with ex vivo irradiation) at 96 h and 120 h. Since handling of the blood sample is important for CBMN assay during shipment or in the laboratory, our findings showed that blood storage at 22°C or at 5°C up to 96 h appeared to provide insignificant variations of the MN results as compared to fresh blood samples. However, the 96 h of blood storage at 5°C elevated the MN frequency in ex vivo irradiated PBL of cancer patients who were undergoing xRT.

The utility of serial complete blood count monitoring in patients receiving radiation therapy for localized prostate cancer

Purpose: It is standard practice in our department to monitor weekly complete blood counts (CBCs) in patients receiving definitive radiation therapy for prostate cancer. The clinical utility and cost effectiveness of this practice has not been analyzed. Methods and Materials: The charts of all prostate cancer patients treated with radiation therapy between January 1994 and July 1996 at the Veterans Administration Hospital, Philadelphia, PA were reviewed. CBC values were available for 89 patients. Patients received a median dose of 68 Gy using a four-field box technique and megavoltage photons. Whole-pelvic radiotherapy followed by a conedown to the prostate was administered to 29 patients. Fifty-nine patients received radiation to the prostate alone or prostate and seminal vesicles. Fifty-seven patients received concurrent hormonal therapy which included luteinizing hormone-releasing hormone (LHRH) agonist, antiandrogens, or both. Results: No patient experienced a drop in their hemoglobin, white blood cells (WBCs), or platelets below critical nadirs (defined as WBC < 2 counts × 1000/mm 3, hemoglobin < 8 g/dl, platelet < 50 counts × 1000/mm 3) at any point during treatment. Thirty-one percent, 25%, and 47% of patients experienced declines of > 50 in platelets, > 2 in WBCs, and > 1 in hemoglobin, respectively. Eight clinical, treatment-related, and pathologic parameters were examined as prognostic factors for a drop of > 2 in hemoglobin, > 2 in WBCs, and > 50 in platelets. Only stage (T3 and above) was significantly associated with a > 2 hemoglobin decline. The use of hormonal therapy was associated with a platelet drop of > 50. None of the 8 prognostic factors were associated with decline of > 2 in WBCs. In the urban area surrounding the Philadelphia Veterans Administration Medical Center, the cost of obtaining a CBC is approximately $30. However, if staff time is considered, the cost of obtaining a weekly CBC during prostate cancer radiotherapy approached $400 per patient. Conclusion: These results suggest that weekly monitoring of CBCs in prostate cancer patients undergoing definitive radiotherapy may not be necessary. We recommend a baseline CBC be performed, and if normal, no other monitoring unless clinically indicated. This strategy would result in a cost savings approaching $30,000 per 100 treated patients. Further research on the cost effectiveness and utility of serial blood tests in patients receiving partial body radiation therapy is needed.

Long-term genetic and reproductive effects of ionizing radiation and chemotherapeutic agents on cancer patients and their offspring.

The continuing search for a cure for cancer has lead to more aggressive therapies as new agents are developed with largely unknown late complications. Standard therapy for the majority of cancers today, following surgery, often consists of combinations of high doses of radiation and multi-drug therapy. Compared with exposures experienced by atomic bomb survivors, cancer survivors have been exposed to higher doses of partial body irradiation and combination chemotherapy over longer periods. Thus, cancer survivors provide a model system with which to evaluate the long-term effects on the human organism of high doses of agents known to damage DNA. Five-year survival after cancer diagnosis is now greater than 56%; more than 5 million Americans are considered cured of cancer. However, the late complications of cancer in long-term survivors has been poorly evaluated, especially in adults, and little is known of the most troubling possibility, that is, that the effects of cancer treatments could be passed on to the next generation. What little we know comes from studies of at most 5,000 survivors of childhood cancer, treated decades ago. So far, results are reassuring that with the means now available, we cannot detect clinical evidence of heritable damage. However, reproductive effects, including infertility, are common consequences of cancer therapy and may represent germ cell damage. We are just in the infancy of studies of germ cell mutagenesis in cancer survivors. The relatively small numbers of survivors, and the few types of exposures studied so far, provide only limited grounds for reassurance. More comprehensive, properly designed, studies of modern new agents are urgently need.

Measurements of the equivalent whole-body dose duringradiation therapy by cytogenetic methods

Estimates of equivalent whole-body dose following partial body exposure can be performed using different biophysical models. Calculations should be compared with biodosimetry data, but measurements are complicated by mitotic selection induced in target cells after localized irradiation. In this paper we measured chromosomal aberrations in peripheral blood lymphocytes during radiotherapy, and estimated the equivalent whole-body dose absorbed, by using the novel technique of interphase chromosome painting. Premature chromosome condensation was induced in stimulated lymphocytes by incubation in calyculin A, and slides were hybridized in situ with whole-chromosome DNA probes specific for human chromosomes 2 and 4. Reciprocal exchanges were used to estimate the equivalent whole-body dose, based on individual pre-treatment in vitro calibration curves. Equivalent whole-body dose increased as a function of the number of fractions, and reached a plateau at high fraction numbers. Chromosomal aberration yields were dependent on field size, tumour position and concurrent chemotherapy. Results suggest that interphase chromosome painting is a simple technique able to give a reliable estimate of the equivalent whole-body dose absorbed during therapeutic partial-body irradiation.

The role of blood stem cells in hematopoietic cell renewal.

It has been the purpose of this keynote address to review available evidence for the notion that the stem and progenitor cells circulating in the peripheral blood play a decisive role in the homeostasis of blood cell formation distributed throughout dozens of bone marrow units in the skeleton. Furthermore, if this notion is correct, one could speculate that the quantity and quality of stem and progenitor cells in the blood should reflect the functional state of the hematopoietic stem cell system throughout the skeletal bone marrow and provide a new tool for the evaluation of alteration in blood cell production. On this basis, the following questions are considered: A) What do we know about the quality and quantity of blood stem cells in steady state conditions? B) In what way do blood stem cells respond to perturbations of the "steady state" of blood cell formation? C) Which role do blood stem cells play during hemopoietic development assuming that the establishment of bone marrow hemopoiesis requires the "seeding" of blood stem cells into an appropriate cellular environment? D) What is the role of blood stem cells in hemopoietic regeneration after partial body irradiation with a small volume of marrow (and hence stem cells) protected? and E) What are the mechanisms and/or kinetics of hemopoietic recovery if stem cells introduced into the circulation were collected from exogenous (autologous or allogeneic) sources? In this review presentation, experimental work of our group and of other members of the scientific community is summarized. It becomes obvious that blood stem and progenitor cells play a key role in hematopoietic homeostasis. Furthermore, their physiology and pathophysiology deserve rigorous experimental studies in order to develop a novel tool in the diagnosis and prognosis of neoplastic and non-neoplastic disorders of blood cell formation.

Effect of ex vivo hyperthermia on radiation-induced micronuclei in lymphocytes of cancer patients before and during radiotherapy

To investigate the effect of ex vivo hyperthermia (HT) and 137 Cs -irradiation on micronucleus (MN) production in cytokinesis-blocked lymphocytes, we obtained the peripheral blood samples from the same cancer patients ( n=6) before and during fractionated partial-body radiotherapy (xRT). The whole blood cultures were heated at 43.5°C for 60 min, followed by 137 Cs irradiation (0–4 Gy). The control cultures from the same patients were incubated at 37°C after being exposed to radiation. The lymphocytes were then stimulated with PHA. Cytochalasin B was applied at 44 h, and lymphocytes were harvested at 72 h. MN frequency was determined on Giemsa-stained slides. We found that in patients before xRT, HT (43.5°C) significantly increased the MN yield (mean±SEM) in unirradiated lymphocytes from 15.6±2.8 (37°C) to 39.7±10.9. Further, in patients either before or during xRT, when the lymphocytes were treated with HT (43.5°C) and combined with ex vivo irradiation, the MN yield ( Y) could be estimated by a linear equation Y= C+ αD. Our findings indicate that as measured by the MN production in cytokinesis-blocked lymphocytes, HT alone at 43.5°C induced DNA damage. Moreover, it enhanced the radiation-induced cytogenetic damage. Therefore, the application of HT may impair the T-cell function in cancer patients who are receiving radiotherapy.

Concurrent partial body radiation prevents cytokine mobilization of blood progenitor cells: an effect mediated by a circulating factor.

Mobilization of stem and progenitor cells into blood, which facilitates the collection of blood-derived autograft and allograft products, can be accomplished with administration of myelosuppressive chemotherapy, hematopoietic growth factors, or both. Autologous donor indifference to mobilization attempts has been correlated with prior administration of chemotherapy and radiation therapy. To investigate whether concurrent administration of radiation therapy inhibits mobilization, five daily injections of a potent combination of mobilizing cytokines, 500 U/kg erythropoietin (EPO) plus 15 microg/kg G-CSF, were administered each morning to Balb/c mice. Each afternoon, a 2 Gy fraction of Co-60 radiation was administered to either the lower limb or the upper or lower hemibody. Each day, mice were necropsied, and blood stem cell mobilization was determined by assaying the number of hematopoietic colony-forming cells in the blood and in the spleen. Unirradiated cytokine-injected mice showed a significant mobilization effect evident as increased colony-forming cells in blood and spleen compared with saline-injected unirradiated controls. The irradiated mice showed markedly inhibited or absent mobilization regardless of the part of the body irradiated. To investigate the mechanism of radiation-induced mobilization inhibition, heparinized plasma was obtained from mice whose lower bodies were irradiated with 2 Gy 18 h previously, and 0.5 ml was injected i.v. into intact mice 10 min before they received 15 microg/kg G-CSF and 500 U/kg EPO. Unlike mice that received G-CSF + EPO only and showed mobilization of progenitors from marrow to spleen, recipients of plasma from irradiated mice before and after cytokine administration showed significantly reduced mobilization of progenitors. Thus, radiation-induced inhibition of stem cell mobilization is mediated by an unidentified circulating factor.

New Developments in Chromosomal Analysis for Biological Dosimetry

Biological dosimetry by dicentric analysis has proved useful on many occasions. An example is given where cytogenetics combined with physical methods have been used to estimate dose in a recent serious over-exposure. The value of dose information for the physician is emphasised since dose can be related to risk of deterministic and stochastic consequences to health. A major new development, FISH, for visualising stable translocations, is discussed with respect to its applicability as a retrospective dosemeter. An example is given where a credihle estimate of dose was obtained 11 years after a uniform whole-body accidental exposure. A cautionary note is raised, illustrated by an in vitro experiment, indicating that non-uniform or partial body irradiation may cause the translocation yield to decrease with time. Finally, comments are made on the effort required and the limits of low dose resolution that FISH offers, which must he considered if the technique is to be used for retrospectively evaluating populations exposed to widespread environmental contamination by radionuclides.

Detection of total- and partial-body irradiation in a monkey model: a comparative study of chromosomal aberration, micronucleus and premature chromosome condensation assays

Purpose: To investigate the efficacy of three cytogenetic methods (dicentrics, micronuclei (MN) and premature chromosome condensation (PCC) analysis) for assessment of the unirradiated fraction and the persistence of damage after total-body (TB) and partial-body (PB) irradiation of rhesus monkeys (Macaca mulatta) . Materials and methods: Animals were exposed to X-rays (5 Gy), either TB or PB, with about 6 % of marrow cells shielded. Blood samples were collected at different times after exposure, i.e. 1, 3 and 7 days, and cultures were set up for the different cytogenetic endpoints. In addition, blood count analysis was performed before and after irradiation. Results: Blood count analysis was not suitable for discriminating between TB and PB exposure. By using Poisson or overdispersion distribution as the basis, it was not possible to distinguish TB from PB irradiation when dicentric chromosomes and MN were analysed. PCC analysis, in contrast, showed a Poisson distribution after TB exposure and overdispersion after PB exposure. Using the PCC assay, reliable dose estimates could be obtained up to 7 days after irradiation. Conclusions: For dicentrics and MN, shielding of 6 % of bone marrow cells was found to be too small to estimate the unirradiated fraction accurately. The PCC technique was useful for dose assessment and the inhomogeneous exposure of 6 % was detected within a short period of time after exposure.