Chromosomal Radiosensitivity in Secondary‐Progressive Multiple Sclerosis Patients

Purpose: To investigate chromosomal radiosensitivity of secondary progressive (SP) multiple sclerosis (MS) patients in comparison to a group of healthy individuals.

Material and methods: Chromosomal radiosensitivity was assessed in vitro with the G2 assay and the G0‐micronucleus (MN) assay. For the G2 assay phytohaemagglutinin (PHA) stimulated blood cultures were irradiated with a dose of 0.4?Gy ⁶⁰Co γ rays in the G2 phase of the cell cycle. For the MN assay unstimulated diluted blood samples were exposed to 3.5?Gy ⁶⁰Co γ rays delivered at a high dose‐rate (HDR=1?Gy/min) or low dose‐rate (LDR=4 mGy/min).

Results: No significant differences in the number of chromatid breaks were observed between MS patients and healthy individuals. With the G0‐MN assay a higher spontaneous MN yield was found in MS patients. At HDR irradiation no significant differences were shown, while at LDR irradiation, MS patients were found less sensitive than healthy controls. The dose‐rate sparing index was higher for MS patients, pointing to a better repair capacity.

Conclusions: MS patients are not characterised by an enhanced in vitro chromosomal radiosensitivity. The radioresistant response, which was only observed with the MN assay after LDR irradiation, may point to an adaptive response induced by in vivo oxidative stress in SPMS patients.     

Chromosomal radiosensitivity study of temporary nuclear workers and the support of the adaptive response induced by occupational exposure

Purpose : To study chromosomal radiosensitivity in a population of radiation workers and investigate the possibility of an adaptive response in lymphocytes of workers after short-term occupational exposure to ionizing radiation. Materials and methods : The studied group comprised 41 workers temporarily employed at the Nuclear Power Plant Doel (Belgium) for reactor maintenance. A blood sample was taken before and directly after the exposure period of about 1 month. Chromosomal radiosensitivity was assessed in vitro by the G2 assay and the G0 micronucleus (MN) assay. For the MN assay, a low dose-rate (LDR) in vitro irradiation protocol was applied in addition to high dose-rate (HDR) irradiation of the blood samples in order to determine the dose-rate sparing (DRS) effect. Results : No statistically significant effect of the occupational exposures (up to 10 mSv) on the baseline MN frequencies without in vitro irradiation was observed. A comparison of the number of chromatid aberrations pre- and post-exposure shows no effect of the occupational exposure. On the other hand, the G0-MN assay with the LDR irradiation protocol reveals a systematic reduction in chromosomal radiosensitivity by the exposure, increasing with dose. For workers who received the highest dose (4-10 mSv) a statistically significant (p < 0.05) decrease of the in vitro induced MN yields and increase of the dose-rate sparing was observed. Conclusions : Short-term low-dose occupational exposure may act as an in vivo adaptive dose and stimulate repair in G0 lymphocytes.     

Chromosomal radiosensitivity study of temporary nuclear workers and the support of the adaptive response induced by occupational exposure

PURPOSE: To study chromosomal radiosensitivity in a population of radiation workers and investigate the possibility of an adaptive response in lymphocytes of workers after short-term occupational exposure to ionizing radiation. MATERIALS AND METHODS: The studied group comprised 41 workers temporarily employed at the Nuclear Power Plant Doel (Belgium) for reactor maintenance. A blood sample was taken before and directly after the exposure period of about 1 month. Chromosomal radiosensitivity was assessed in vitro by the G2 assay and the G0 micronucleus (MN) assay. For the MN assay, a low dose-rate (LDR) in vitro irradiation protocol was applied in addition to high dose-rate (HDR) irradiation of the blood samples in order to determine the dose-rate sparing (DRS) effect. RESULTS: No statistically significant effect of the occupational exposures (up to 10 mSv) on the baseline MN frequencies without in vitro irradiation was observed. A comparison of the number of chromatid aberrations pre- and post-exposure shows no effect of the occupational exposure. On the other hand, the G0-MN assay with the LDR irradiation protocol reveals a systematic reduction in chromosomal radiosensitivity by the exposure, increasing with dose. For workers who received the highest dose (4-10 mSv) a statistically significant (p <0.05) decrease of the in vitro induced MN yields and increase of the dose-rate sparing was observed. CONCLUSIONS: Short-term low-dose occupational exposure may act as an in vivo adaptive dose and stimulate repair in G0 lymphocytes.     

Chromosomal radiosensitivity in BRCA1 and BRCA2 mutation carriers

Purpose: The chromosomal radiosensitivity of a selected group of familial breast cancer patients carrying a mutation in BRCA1 (n=11) or BRCA2 (n=9) and a group of healthy mutation carriers (n=12) was investigated and compared to a reference group of breast cancer patients without a BRCA1/2 mutation (n=78) and a group of healthy women carrying no mutation (n=58).

Materials and methods: The chromosomal radiosensitivity was assessed with the G2 and the G0‐micronucleus (MN)‐assay on fresh blood samples and on Epstein‐Barr virus (EBV)‐transformed lymphoblastoid cell lines. For the MN‐assay, lymphocytes were exposed in vitro to 3.5?Gy and 2?Gy ⁶⁰Co γ‐rays at a high dose rate (HDR) or low dose rate (LDR). 70‐h post‐irradiation cultures were arrested and micronuclei were scored in 1000 binucleate cells. For the G2‐assay lymphocytes were irradiated in vitro with a dose of 0.4?Gy ⁶⁰Co γ‐rays after 71h incubation. Cultures were arrested 90?min after irradiation and chromatid breaks were scored in 50 metaphases.

Results: The group of breast cancer patients with a BRCA1 or 2 mutation was on average more radiosensitive than the control group, but not different from breast cancer patients without a BRCA mutation. The radiation response of healthy BRCA1/2 carriers was not significantly different from the control group and also not different from relatives without a BRCA mutation. Comparing the radiation response in EBV cell lines derived from breast cancer patients with or without a BRCA1 mutation revealed no significant difference. Conclusions: Our results reveal that chromosomal radiosensitivity observed in breast cancer patients heterozygous for BRCA1 or 2 mutations, could not be demonstrated in healthy BRCA1/2 mutation carriers. This suggests that mutations in BRCA1 or 2 genes are not playing a main role in chromosomal radiosensitivity, this although BRCA1 and 2 are both involved in DNA repair/signalling processes.     

Chromosomal radiosensitivity in BRCA1 and BRCA2 mutation carriers

PURPOSE: The chromosomal radiosensitivity of a selected group of familial breast cancer patients carrying a mutation in BRCA1 (n=11) or BRCA2 (n=9) and a group of healthy mutation carriers (n=12) was investigated and compared to a reference group of breast cancer patients without a BRCA1/2 mutation (n=78) and a group of healthy women carrying no mutation (n=58). MATERIALS AND METHODS: The chromosomal radiosensitivity was assessed with the G2 and the G0-micronucleus (MN)-assay on fresh blood samples and on Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines. For the MN-assay, lymphocytes were exposed in vitro to 3.5 Gy and 2 Gy 60Co gamma-rays at a high dose rate (HDR) or low dose rate (LDR). 70-h post-irradiation cultures were arrested and micronuclei were scored in 1000 binucleate cells. For the G2-assay lymphocytes were irradiated in vitro with a dose of 0.4 Gy 60Co gamma-rays after 71h incubation. Cultures were arrested 90 min after irradiation and chromatid breaks were scored in 50 metaphases. RESULTS: The group of breast cancer patients with a BRCA1 or 2 mutation was on average more radiosensitive than the control group, but not different from breast cancer patients without a BRCA mutation. The radiation response of healthy BRCA1/2 carriers was not significantly different from the control group and also not different from relatives without a BRCA mutation. Comparing the radiation response in EBV cell lines derived from breast cancer patients with or without a BRCA1 mutation revealed no significant difference. CONCLUSIONS: Our results reveal that chromosomal radiosensitivity observed in breast cancer patients heterozygous for BRCA1 or 2 mutations, could not be demonstrated in healthy BRCA1/2 mutation carriers. This suggests that mutations in BRCA1 or 2 genes are not playing a main role in chromosomal radiosensitivity, this although BRCA1 and 2 are both involved in DNA repair/signalling processes.     

The use of cryopreserved lymphocytes in assessing inter-individual radiosensitivity with the micronucleus assay

PURPOSE: The feasibility of using cryopreserved lymphocytes to detect inter-individual differences in chromosomal radiosensitivity was investigated. Typically, such studies are conducted with fresh blood samples but, in a clinical setting, when availability of samples is unpredictable, this is not always convenient. The sensitivity of 23 normal healthy donors, 11 breast cancer patients who had shown severe acute skin reactions to radiotherapy and seven ataxia telangiectasia (A-T) heterozygotes was determined. MATERIALS AND METHODS: Thawed lymphocytes were exposed to high (HDR) or low dose rate (LDR) gamma irradiation (3.5 Gy) in Go, stimulated with PHA, treated with cytochalasin-B 24 h later and then harvested at 90 h for the determination of micronucleus (MN) yields in binucleate cells. RESULTS: Each normal donor was tested one to three times. Mean MN yields were 76.1 +/- 9.3/100 cells at HDR and 44.5 +/- 5.3 at LDR, giving an LDR sparing effect of 39.6 +/- 9.3%. A relatively high proportion of tests failed to yield sufficient binucleate cells for analysis. Inter-experimental variability was also high and it was not possible to demonstrate inter-individual differences in sensitivity in spite of the use of an internal control sample from a single normal donor in each experiment. There was a small but significant increase in radiation-induced MN in the breast cancer patients compared with the normals at LDR (but not at HDR), but a complete overlap with the normal range. There was no increase in sensitivity in the A-T heterozygotes at HDR. The LDR samples failed because the LDR protocol reduced proliferation rates, and radiation-induced mitotic inhibition in this group was higher than in normals. CONCLUSIONS: In comparison with previous experience with fresh blood samples, the use of frozen lymphocytes is not as satisfactory because: (1) experimental failures are higher; (2) inter-experiment variability is higher: (3) dose-rate sparing is lower, suggesting poorer repair; and (4) the ability to discriminate between breast cancer cases and normals is probably lower.     

Influence of dose-rate, post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes.

PURPOSE: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. MATERIALS AND METHODS: Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3 Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). RESULTS: A significant decrease in reproductive cell death was observed after 3 Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDRI analysed day 6, although not of statistical significance. Radiation-induced apoptosis was efficiently counteracted by growth factors up to 24-48 h after 3 Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR 1 cells plated day 6), a significant increase in reproductive cell death was found (3 Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR 1 plated day 1 and HDR6). CONCLUSIONS: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.     

Influence of dose-rate,post-irradiation incubation time and growth factors on interphase cell death by apoptosis and clonogenic survival of human peripheral lymphocytes

Purpose: To investigate the effects of dose-rate, post-irradiation incubation time and growth factors on radiation-induced interphase cell death by apoptosis and reproductive cell death in human peripheral lymphocytes. Materials and methods : Lymphocytes in G0-phase were exposed in vitro to 1-3Gy 137Cs gamma-radiation at a high- (HDR, 45Gy/h) or a low dose-rate (LDR, 0.024Gy/h). HDR exposures were performed either on day 1 (HDR1) simultaneously with the start of the 3Gy LDR exposure, or on day 6 (HDR6) when the LDR exposures ended. Apoptosis was studied at different times after irradiation by measuring (1) cellular membrane integrity, (2) morphological changes and (3) cell size reduction. Clonogenic survival was analysed for cells plated directly after irradiation (LDR, HDR6, HDR1 day 1) or after 5 days post-irradiation incubation (HDR1 day 6). Results: A significant decrease in reproductive cell death was observed after 3Gy LDR exposure as compared with the HDR1 exposure for cells plated day 6. For the lower doses applied, the dose-rate effect could not be statistically verified. A decrease in apoptosis for all three doses applied (i.e. 1, 2 and 3Gy) was observed when the LDR exposures were compared with the HDR1 analysed day 6, although not of statistical significance. Radiation-induced apoptosis was e fficiently counteracted by growth factors up to 24-48h after 3Gy HDR exposure. The prevention of radiation-induced cell death by growth factors was dependent on dose and post-irradiation time in G0. When the growth factors were added after a prolonged post-irradiation incubation in G0 (HDR1 cells plated day 6), a significant increase in reproductive cell death was found (3Gy) as compared with HDR protocols where the growth factors were added directly after irradiation (HDR1 plated day 1 and HDR6). Conclusions: A dose-rate effect on radiation-induced apoptosis was indicated but not statistically verified. A significant dose-rate effect on reproductive cell death was observed. This dose-rate effect was, however, inverted when growth factors were added directly after the HDR irradiations.     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

PURPOSE: Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed "low-dose hyper-radiosensitivity" (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h(-1). We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. MATERIALS AND METHODS: T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h(-1) using a (60)Co gamma-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. RESULTS: LDR at > or = 60 cGy h(-1) to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h(-1), but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h(-1) or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the "degree" of acute-dose HRS, as measured by alpha(s), was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. CONCLUSIONS: Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

Purpose : Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed 'low-dose hyper-radiosensitivity' (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h -1. We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. Materials and methods : T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h -1 using a 60 Co γ-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. Results : LDR at ≥60 cGy h -1 to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h -1, but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h -1 or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the 'degree' of acute-dose HRS, as measured by α s, was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. Conclusions : Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

Comparison of cellular damage response to low-dose-rate 125I seed irradiation and high-dose-rate gamma irradiation in human lung cancer cells

PurposeTo investigate the difference of cellular response between low-dose-rate (LDR) ¹²⁵I seed irradiation and high-dose-rate (HDR) γ-irradiation in human lung cancer cells.Methods and MaterialsA549 and NCI-H446 cells with or without wortmannin (WM) treatment were exposed to ¹²⁵I seeds and γ-rays, respectively. Cell survival, micronuclei (MN) formation, and the expressions of Ku70/Ku80 proteins were measured.ResultsThere was a strong negative correlation between survival and MN formation for both irradiations, and the MN inductions of NCI-H446 were about twofolds of those of A549, and the survival of NCI-H446 was lower than that of A549, indicating the radiosensitivity of NCI-H446 cells was greater than that of A549 cells. Interestingly, at 4-Gy radiation, NCI-H446 cells were more sensitive to LDR irradiation than HDR irradiation. WM treatment enhanced the radiosensitivity of A549 cells evenly to ¹²⁵I seed and γ-irradiation, but this treatment led NCI-H446 cells to be more sensitive to LDR ¹²⁵I. Further results revealed that the expression of phosphorylated Ku80 protein was enhanced in irradiated A549, but in contrast, it was markedly decreased in NCI-H446 cells after 4-Gy LDR ¹²⁵I irradiation as that compared with γ-irradiated and nonirradiated cells.ConclusionNCI-H446 cells were more sensitive to LDR ¹²⁵I irradiation than HDR irradiation, and this sensitivity could be further enhanced by WM treatment. But no obvious differences of cellular response to both irradiations were observed in A549. Ku as molecular markers together with cell proliferation rate can be used to predict the radiosensitivity of tumor cells to LDR ¹²⁵I seed irradiation.     

Contrasting Dose-rate Effects of γ-irradiation on Rat Salivary Gland Function

The aim of this study was to investigate the effects of ⁶⁰Co irradiation delivered at high (HDR) and low (LDR) dose-rates on rat salivary gland function. Total-body irradiation (TBI; total doses 7·5, 10 and 12·5 Gy) was applied from a ⁶⁰Co source at dose-rates of 1 cGy/min (LDR) and 40 cGy/min (HDR) followed by syngeneic bone marrow rescue. Four days before and 1–30 days after TBI, submandibular and parotid saliva samples were collected in male albino Wistar rats using Lashley cups. Lag phase and flow rate were recorded, and [Na⁺] and [K⁺] were measured. The severity of salivary gland dysfunction for each dose-rate was dependent on total TBI dose in all parameters. LDR irradiation significantly enhanced the increase of lag phase, while it tended to further decrease flow rate during days 0–3. At later times the reverse effect was seen with significant LDR sparing in most cases. The changes in [Na⁺] and [K⁺] showed similar trends; LDR had an enhancing effect for early damage, while beyond day 3 it consistently produced less damage. From this dose-rate study it is concluded that the early postirradiation changes in salivary gland function are probably predominantly caused by irradiation damage to membrane structures and are less the result of reproductive failure. The later changes in salivary gland function are probably mainly dependent on repopulation of surviving stem cells.     

A higher micronucleus yield in B- versus T-cells after low-dose γ-irradiation is not linked with defective Ku86 protein

Purpose : To elaborate the B-cell micronucleus (MN) response in the low-dose region in detail and to investigate the postulated deficiency in DNA-PK in B-cells. Materials and methods : Lymphocytes of five healthy volunteers were irradiated with low LET γ-rays and high LET fast neutrons with doses ranging between 0.01 and 2 Gy. After post-irradiation incubation, B- and T-cells were isolated via CD3 and CD19 immunomagnetic microbeads. MN were analysed in both subpopulations. To study the underlying mechanism of chromosomal radiosensitivity, cell extracts prepared from purified B- and T-cells were subjected to SDS-electrophoresis and electroblotting using antibodies directed against the DNA-PK repair enzymes Ku70/86 and DNA-PKcs. Activity measurements were performed using the SignaTECT DNA-dependent protein kinase assay. DNA double-strand break (DSB) induction and rejoining was determined using constant-field gel electrophoresis. Results : For low LET γ-rays a higher MN yield was observed in B-cells than in T-cells, but only in those samples exposed to doses < 1Gy. For 1 Gy, the MN yields were comparable and for 2 Gy even lower in B-cells compared with T-cells. After high LET neutron irradiation no significant differences in MN yields were observed between both subsets. The results of the DNA-PK experiments demonstrate that there is no difference between T- and B-cells in the basal expression and activity of DNA-PK repair proteins. No differences in DNA DSB induction and rejoining were found between T- and B-cells using constant-field gel electrophoresis. Conclusions : From the results, it was concluded that the enhanced chromosomal radiosensitivity in B-cells is restricted to low doses (<1 Gy) of low LET radiation and that the chromosomal behaviour of B-cells to low LET radiation cannot be attributed to aberrant forms of the DNA-PK components. A type of chromosomal induced radioresistance (IRR) may be a possible explanation for the observed effect.     

A higher micronucleus yield in B-versus T-cells after low-dose gamma-irradiation is not linked with defective Ku86 protein

PURPOSE: To elaborate the B-cell micronucleus (MN) response in the low-dose region in detail and to investigate the postulated deficiency in DNA-PK in B-cells. MATERIALS AND METHODS: Lymphocytes of five healthy volunteers were irradiated with low LET gamma-rays and high LET fast neutrons with doses ranging between 0.01 and 2 Gy. After post-irradiation incubation, B- and T-cells were isolated via CD3 and CD19 immunomagnetic microbeads. MN were analysed in both subpopulations. To study the underlying mechanism of chromosomal radiosensitivity, cell extracts prepared from purified B- and T-cells were subjected to SDS-electrophoresis and electroblotting using antibodies directed against the DNA-PK repair enzymes Ku70/86 and DNA-PKcs. Activity measurements were performed using the SignaTECT DNA-dependent protein kinase assay. DNA double-strand break (DSB) induction and rejoining was determined using constant-field gel electrophoresis. RESULTS: For low LET gamma-rays a higher MN yield was observed in B-cells than in T-cells, but only in those samples exposed to doses < 1 Gy. For 1 Gy, the MN yields were comparable and for 2Gy even lower in B-cells compared with T-cells. After high LET neutron irradiation no significant differences in MN yields were observed between both subsets. The results of the DNA-PK experiments demonstrate that there is no difference between T- and B-cells in the basal expression and activity of DNA-PK repair proteins. No differences in DNA DSB induction and rejoining were found between T- and B-cells using constant-field gel electrophoresis. CONCLUSIONS: From the results, it was concluded that the enhanced chromosomal radiosensitivity in B-cells is restricted to low doses (<1 Gy) of low LET radiation and that the chromosomal behaviour of B-cells to low LET radiation cannot be attributed to aberrant forms of the DNA-PK components. A type of chromosomal induced radioresistance (IRR) may be a possible explanation for the observed effect.     

Chromosome aberrations detected by FISH and correlation with cell survival after irradiation at various dose-rates and after bromodeoxyuridine radiosensitization

PURPOSE: To determine whether measurement of chromosome aberrations by fluorescence in situ hybridization (FISH) predicts cell survival after irradiation at different dose-rates and after radiosensitization by bromodeoxyurdine (BrdU) in a lung carcinoma cell line. MATERIALS AND METHODS: The human lung carcinoma cell line SW1573 was irradiated at high dose-rate (HDR: 0.8 Gy min-1) or at pulsed low dose-rate (p-LDR: average dose-rate 1 Gy h-1) with or without radiosensitization by bromodeoxyuridine (BrdU). Cell survival was determined by clonogenic assay. Chromosome aberrations (colour junctions) were measured by whole-chromosome FISH of chromosome 2 and 18 and were scored according to the PAINT method. RESULTS: Clear radiosensitization by BrdU was observed both after HDR and p-LDR irradiation. Chromosome 18 was more radiosensitive than chromosome 2. There was a good correlation between induction of colour junctions and cell survival both after HDR and p-LDR irradiation and after radiosensitization by BrdU. CONCLUSIONS: Determination of chromosome aberrations by FISH can predict cell survival after different dose-rates and after radiosensitization by BrdU     

Comparison of the radiosensitivity of normal-tissue cells with normal-tissue reactions after radiotherapy

PURPOSE: To investigate whether the in vitro radiosensitivity of normal lymphocytes and fibroblasts evaluated by the micronucleus (MN) assay predicts acute and late reactions after radio-therapy in cancer patients. MATERIALS AND METHODS: Studies were performed on blood samples from 31 cervical and head and neck cancer patients and on skin fibroblasts from eight of the cancer patients. The radiosensitivity of lymphocytes and of fibroblasts was also assessed in 24 and five healthy donors, respectively. Radiosensitivity was measured after in vitro irradiation with doses ranging from 2 to 5 Gy using micronucleus frequency (the number of micronuclei per single binucleated (BN) cell) and the percentage of BN cells with micronuclei. The in vitro results were compared with the maximum grade of acute and late reactions. RESULTS: There was no significant difference in cellular radiosensitivity between cancer patients and healthy donors. Although cancer patients differed considerably in normal-cell radiosensitivity, no correlation was found between radiosensitivity, either of lymphocytes or fibroblasts, and acute and late clinically observed side effects. In addition, no relationship was observed between the radiosensitivity of lymphocytes and fibroblasts derived from the same donors. CONCLUSION: The data do not support the usefulness of the MN assay in predicting normal-tissue response to radiotherapy in cancer patients.     

Comparison of the radiosensitivity of normal-tissue cells with normal-tissue reactions after radiotherapy

Purpose : To investigate whether the in vitro radiosensitivity of normal lymphocytes and fibroblasts evaluated by the micronucleus (MN) assay predicts acute and late reactions after radiotherapy in cancer patients. Materials and methods : Studies were performed on blood samples from 31 cervical and head and neck cancer patients and on skin fibroblasts from eight of the cancer patients. The radiosensitivity of lymphocytes and of fibroblasts was also assessed in 24 and five healthy donors, respectively. Radiosensitivity was measured after in vitro irradiation with doses ranging from 2 to 5 Gy using micronucleus frequency (the number of micronuclei per single binucleated (BN) cell) and the percentage of BN cells with micronuclei. The in vitro results were compared with the maximum grade of acute and late reactions. Results : There was no significant difference in cellular radiosensitivity between cancer patients and healthy donors. Although cancer patients differed considerably in normal-cell radiosensitivity, no correlation was found between radiosensitivity, either of lymphocytes or fibroblasts, and acute and late clinically observed side effects. In addition, no relationship was observed between the radiosensitivity of lymphocytes and fibroblasts derived from the same donors. Conclusion : The data do not support the usefulness of the MN assay in predicting normal-tissue response to radiotherapy in cancer patients.     

Low-Dose-Rate versus High-Dose-Rate intracavitary brachytherapy in cervical cancer - Final Results of a Phase III randomized trial

PURPOSEIntracavitary brachytherapy using High-Dose-Rate (HDR) and Low-dose-rate (LDR) in cervical cancer has been utilized. We report the long-term final results of a large randomized trial in terms of toxicities and efficacy.METHODS AND MATERIALSBetween 1996 to 2005, 816 patients were randomized to LDR (n = 441 patients) or HDR brachytherapy (n = 369 patients) stratified by FIGO Stage grouping. Patients with Stage I-II received external irradiation of 40 Gy in 20 fractions (with midline block (MLB)) followed by either 2 LDR Intracavitary applications of 30 Gy to point A (2–3 weeks apart) or 5 HDR Intracavitary applications of 7 Gy to point A once weekly. Patients with Stage III received 50 Gy in 25 fractions (with MLB after 40 Gy) followed by either one application of LDR 30 Gy to point A or three applications of HDR 7 Gy to point A once weekly.RESULTSWith a median follow-up was 64 months (interquartile range [IQR]: 21 - 111), moderate to severe rectal and bladder complications were higher in LDR arm as compared to HDR arm (9.7% vs. 3.6%; p = 0.02) and (10.5% vs. 5.5%; p = 0.06) for Stage I-II. No difference in rectal or bladder complications for Stage III patients. Disease free and overall survivals were similar in both the arms for all stages.CONCLUSIONSHDR intracavitary brachytherapy with 7 Gy per fraction weekly is superior to LDR in terms of late rectal and bladder complications. Local control rates and survivals are similar irrespective of stages.     

肿瘤细胞对p(35)Be快中子的辐射敏感性研究

目的 比较肿瘤细胞p(35)Be块中子及γ射线的辐射敏感性,为肿瘤的快中子治疗提供理论依据。方法 用细胞集落在存活方法研究人黑色素瘤细胞（WM9839）、人口 皮癌细胞（KB）、人结肠腺癌细胞（LS－T－117）和人前列腺癌细胞（PC3M）等4种细胞对快中子及γ射线的辐射敏感性,用彗星电泳技术研究WM9839细胞在快中子及γ射线照射后DNA损伤的修复效应。结果 细胞存活实验表明,p(35)Be快中子照射后4种肿瘤细胞的D0值（或SF2值）较γ射线照射后差异减小,即4种肿瘤细胞对快中子的辐射敏感性差异减小;快中子2Gy照射后,WM9839细胞DNA损伤修复曲线整体上下降较γ射线2Gy照射后慢,到180min时,DNA损伤残留率明显高于γ射线2Gy照射。结论 快中子治疗肿瘤可以很好地弥补低LET射线放射治疗的不足,特别是对低LET射线较为耐受的肿瘤细胞,如KB细胞和WM98309细胞。     

Radiosensitivity in patients suffering from chronic kidney disease

Abstract

Purpose: Patients suffering from chronic kidney disease (CKD) exhibit a high incidence of cancer, as well as high levels of genetic damage. We hypothesized that these patients show genomic instability detected as an increased chromosomal radiosensitivity in front of the genetic damage induced by ionizing radiation.

Material and methods: The background levels of genetic damage and the net genetic damage after in vitro irradiation with 0.5 Gy were analyzed using the micronucleus (MN) assay in peripheral blood lymphocytes. A total number of 552 individuals (179 controls and 373 CKD patients) were included in the study.

Results: The net radiation-induced genetic damage was significantly higher in CKD patients than in controls; but no differences between those patients submitted to hemodialysis and those in pre-dialytic stages were detected. A positive correlation was observed between basal and net micronucleus frequencies in CKD patients what would indicate an underlying genetic background modulating DNA damage levels.

Conclusions: Our results indicate that CKD patients present genomic instability, measured as an increased chromosomal radiosensitivity in front of ionizing radiation.