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At least 955 records · Page 53Linked to original sources
PubMedDate not supplied

[A decrease in the efficiency of radiation damage repair in HeLa tumor cells with their preliminary irradiation at low radiation doses (0.1 Gr)].

In experiments with tumor HeLa cells, a study was made of the survival rate of both the whole population and individual clonogenic cells after irradiation within different regimes at a cumulative dose of 4 Gy. The results obtained prompt a conclusion that the preirradiation with a dose of 0.1 Gy decreases the efficiency of repair of radiation-induced damages to cells.

Cell Survival↗
PubMedDate not supplied

[The equivalent dose as a dosimetric criterion for acute radiation injury by radiations of various quality. The generalized equivalent dose].

Using different quality coefficients as functions of LET, generalized equivalent doses were calculated, and the survival of dogs after gamma/neutron irradiation was determined using the concept of an equivalent dose. LET functions of the generalized quality coefficients providing a good agreement between theoretical and experimental results were chosen. Various functions of the generalized quality coefficients for different ingredients of bone-marrow haemopoiesis activity should be used to estimate the severity of radiation injury to red bone marrow.

Animals↗
PubMedDate not supplied

[The action of gamma radiation and secondary proton radiation with 70-GeV energy on different mammalian cells].

The sensitivity to gamma- and secondary proton (70 GeV) radiation was studied in fibroblast cell culture of Chinese hamster and NIH 3T3 mice and, with respect to survival rate, in lymphoma strains L5178 V-S and L5178 V-R. It was shown that RBE was high for radiosensitive cultures and that the major role in the final biological effect was played by the mode of the postirradiation processes rather than by the peculiarities of the primary injury.

3T3 Cells↗
PubMedDate not supplied

[Radiation exposure of cultured tissue cells and animals (mice) within 10-kilometers zone of accident at Chernobyl nuclear plant. Effect on radiosensitivity to future radiation].

The effect of chronic low-level radiation exposure on radiosensitivity to posterior acute irradiation at high doses has been studied. Cells and mice were exposed within the ten-kilometer zone of Chernobyl disaster during various spaces of time (1-12 days), then over one or more days were additionally irradiated by doses of 1-4 Gy. It was shown that no adaptive response was developed under chronic exposure of cells and mice within the zone of disaster. On the contrary increased sensitivity to posterior irradiation was revealed. The number of cytogenetic damages of cultured tissue cells and marrow cells (chromosome aberrations and micronuclei) increases, the spectrum of aberrations being shifted to chromosome type, cells with multiaberration appearing. The decay of chromatine increases indicating an interphase death; the number of leucocytes in peripheral blood decreases.

Accidents, Occupational↗
PubMedDate not supplied

[Native protein activated by low doses of gamma radiation as a source of secondary biogenic radiation].

If is demonstrated that native protein of egg-white after being gamma-irradiated with law doses is able to stimulate transition of cells of remote biological detector from non-cycling state to proliferation even if irradiated protein is separated from detector by quartz-glass. Animal tissues which have a high protein content (freshly cut hair; insect bodies) reveal the same ability. The role of natural background radiation in the maintenance of energy excitation, state of living tissue proteins is discussed.

Animals↗
PubMedDate not supplied

[The dependence of the biological effect of electron radiation on the pulse repetition rate. The dependence of mortality and life span in rats on the radiation dose and pulse repetition rate].

Quantitative regularities have been established for mortality and life-span of rats in relation to the pulse recurrence frequency (3-2400 s-1) of electron radiation with electron energies of 25 and 50 MeV. Electrons with pulse recurrence frequencies of 600 and 1200 s-1 have shown a higher biological effectiveness.

Animals↗
PubMed1997

Effect of polyamine-induced compaction and aggregation of DNA on the formation of radiation-induced strand breaks: quantitative models for cellular radiation damage.

The yield of DNA single-strand breaks, G(SSB), upon gamma irradiation of SV40 DNA and SV40 minichromosomes in aqueous solution under aerobic conditions was determined at physiological ionic strength in the presence of various potential radioprotective agents. Putrescine (PUT), spermidine (SPD), glutathione, trans-4,5-dihydroxy-1,2-dithiane, 2-mercaptoethyl disulfide and cystamine, all at 0.1-10 mM, spermine (SPM, 0.1-1 mM) and WR-33278 (WRSSWR, 0.1-2 mM) lowered G(SSB) of SV40 DNA. These results were expected from the ability of these agents to scavenge OH radical in the bulk solution. However, SPD, above 10 mM, and SPM and WRSSWR, each above 2 mM, produced dramatic radioprotection attributed to polyamine-induced compaction and aggregation of the DNA (PICA effect). The DNA of SV40 minichromosomes was inherently less radiosensitive and was subject to a PICA effect at lower polyamine concentrations, i.e. approximately 5 mM SPD, approximately 0.6 mM SPM and approximately 0.5 mM WRSSWR. The PICA effect decreased G(SSB) for SV40 DNA and minichromosomes by one to two orders of magnitude, depending upon the scavenging capacity of the medium. The final yields were similar for SV40 DNA and minichromosomes and were comparable to the corresponding yield determined for cells. Results for the yield of double-strand breaks indicated that the yield of double-strand breaks, G(DSB), for DNA and minichromosomes is subject to a PICA effect by SPM and SPD comparable to that measured for G(SSB). Values of G(SSB) for SV40 DNA and minichromosomes subjected to the PICA effect were well approximated by calculations based upon a 30-nm cylinder assumed to model their condensed states. The results indicate that a major fraction of the formation of SSBs in condensed DNA and minichromosomes results from nonscavengeable radical intermediates. Minichromosomes subjected to the PICA effect of 2 mM SPM were protected against formation of radiation-induced SSBs 1.5-fold by 20 mM DTT but 5-fold by 10 mM DTT plus 10 mM WR-1065 relative to 2 mM SPM alone. Thus WR-1065 is capable of providing marked protection of compacted and aggregated minichromosomes, a protection ascribed to the chemical repair of DNA radicals by WR-1065.

Cystamine↗
PubMed1981

Radiation carcinogenesis in man: new primary neoplasms in fields of prior therapeutic radiation.

Nine patients are presented in whom new malignant neoplasms developed in fields of prior irradiation. The prior irradiation had been administered to these patients for previously confirmed cancers, lesions suspected of being cancer (but never confirmed as such), and for non-neoplastic disorders. Each of these cases is relatively unique and several present the first association between prior radiation therapy and the subsequent neoplasm or neoplasms which developed.

Adolescent↗
PubMed1994

White matter changes are correlated significantly with radiation dose. Observations from a randomized dose-escalation trial for malignant glioma (Radiation Therapy Oncology Group 83-02).

BACKGROUND: A Phase I/II randomized dose-seeking trial was performed to document the severity, time course, and significance of white matter changes seen on serial imaging scans (magnetic resonance imaging, computed tomography) associated with bis-chlorethyl nitrosourea (BCNU) and hyperfractionated cranial irradiation. METHODS: Long term survivors (> or = 18 months) were identified from a prospective randomized dose-escalation Phase I/II trial designed to evaluate twice-daily radiotherapy for supratentorial high grade malignant gliomas. All scans were reviewed by a neuroradiologist who had no information about the prescribed dose and fractionation. In the trial, patients were assigned to receive 64.8 Gy, 72.0 Gy, 76.8 Gy, or 81.4 Gy (all fractionated as 1.2 Gy twice a day [bid]), or 48.0 Gy or 54.4 Gy (both in 1.6-Gy bid fractions). Bis-chlorethyl nitrosourea was administered every 8 weeks for 1 year. Of 747 randomized patients, 177 had analyzable scans. The scans reviewed were those acquired preoperatively, immediately postoperatively, 3, 6, 12, and 18 months after radiotherapy. Radiographic endpoints included no white matter change (Grade 0), minimal patchy white matter foci (Grade 1), start of confluence of white matter disease (Grade 2), large confluent areas (Grade 3), confluence with cortical/subcortical involvement (Grade 4), leukoencephalopathy (Grade 5), and possible necrosis (Grade 6) according to the classification of F. Fazekas et al. The effects were scored relative to the baseline preoperative scans. The dose pairs of 48 Gy and 54.4 Gy, 64.8 Gy and 72 Gy, and 76.8 Gy and 81.4 Gy were grouped together for analysis (low, intermediate, and high dose, respectively). Toxicity was analyzed in three ways: Grade 2 or worse, Grade 3 or worse, and Grade 6. RESULTS: Grade 2 or worse changes were observed in 26.6, 27.6, and 40.4% of patients in the low, intermediate, and high dose groups, respectively. Grade 3 or worse changes were observed in 8.3, 20.0, and 36.5% of patients in the low, intermediate, and high dose groups, respectively. Grade 6 changes were observed in 1.6, 4.6, and 19.2% of patients in the low, intermediate, and high dose groups, respectively. No statistically significant differences were observed among treatment groups when toxicity was evaluated as Grade 2 or worse. For toxicity of Grade 3 or worse, an chi-square test revealed P values of 0.04 (low vs. intermediate dose), 0.09 (intermediate vs. high dose), and 0.0005 (low vs. high dose). With the endpoint of possible necrosis (Grade 6), P values were 0.21 (low vs. intermediate dose), 0.05 (intermediate vs. high dose), and 0.003 (low vs. high dose). The median time to radiographic appearance of an effect (15 months) was not influenced by total dose or fraction size. CONCLUSIONS: A well described toxicity scale for white matter injury was applied successfully to patients with malignant glioma treated with definitive irradiation. Severe white matter changes continued to increase significantly as the total dose of hyperfractionated cranial irradiation was escalated. The time to onset of the white matter abnormalities appeared to be independent of dose. An ongoing Radiation Therapy Oncology Group study will allow correlation of white matter injury with prospective neuropsychometric testing.

Brain↗
PubMed1994

The question of threshold doses for radiation damage: malformations induced by radiation exposure of unicellular or multicellular preimplantation stages of the mouse.

Mouse embryos of the one-cell stage or the 32- to 64-cell stage were exposed to various X-ray doses (one-cell stage: 0.25-2 Gy; 32- to 64-cell stage: 1-3 Gy). It turned out that the shape of the dose-response curves is statistically compatible with the assumption derived from biological considerations that there is no threshold for radiation-induced malformations in the case of the exposure of one-cell embryos, whereas there is a threshold dose (close to 1 Gy) in the case of the exposure of 32- to 64-cell embryos.

Animals↗
PubMed1980

Numerical relationship between cells with radiation-induced chromosome aberrations and cells lethally injured by radiation.

The numerical relationship between radiation-induced chromosome aberrations in human G0 lymphocytes and reproductive lethality of human bone-marrow lymphocytes is analysed within a large LET interval. The comparison is based upon the evaluation of the coefficient a of the linear component of the corresponding dose-effect-relation for the frequency of cells without aberrations and for the frequency of surviving cells respectively. The good correlation between these coefficients over a large LET interval supports the hypothesis that structural chromosome aberrations and reproductive cell death both result from the same gross chromatin damage.

Cell Survival↗
PubMed2003

Optimization of radiation therapy for locally advanced adenoid cystic carcinomas with infiltration of the skull base using photon intensity-modulated radiation therapy (IMRT) and a carbon ion boost.

BACKGROUND: Tumor doses > 70 Gy are needed for local control in adenoid cystic carcinomas. These tumor doses cannot be delivered if the tolerance doses to neighboring organs at risk (OAR) are respected. This treatment planning study investigates the physical advantage of combined photon intensity-modulated radiation therapy (IMRT) plus carbon ion boost compared to photon IMRT alone. PATIENTS AND METHODS: For nine patients, treatment plans were generated using a) photon IMRT alone (integrated boost concept), and b) sum plans consisting of a photon IMRT plan and a carbon ion boost plan. 54 Gy were prescribed to the planning target volume 1 (PTV1), the boost volume (PTV2) received 72 Gy. The tolerance doses of the delineated OAR were strictly adhered to. Plan quality of IMRT plans and sum plans was compared using adequate physical parameters. RESULTS: Both therapy techniques lead to highly conformal dose distributions that allow the prescription of the desired target doses. Target conformality and heterogeneity as well as target coverage for PTV1 are comparable for both techniques. The target coverage for PTV2 can be significantly improved using carbon ion beams (median 95% coverage 93.7% vs 87%; p = 0.039). Furthermore, the mean doses to the OAR can be reduced by 8.3% (median % reduction of mean doses to OAR; p = 0.00001) using carbon ions. CONCLUSIONS: The combination of photon IMRT with carbon ions improves the target coverage for the boost volume and offers better sparing of OAR close to the PTV2 (gross tumor volume) in comparison with photon IMRT alone. A clinical study has been initiated to evaluate whether these potential advantages translate into clinical benefit.

Carbon↗
PubMed1999

[Determination of monitor radiation scattering contribution in photon radiation of clinical electron linear accelerators].

BACKGROUND: Modern linear accelerators permit the use of irregular fields due to their flexible collimator systems with separately movable jaws or multileaf collimators. When using such irregular fields in the clinical practice output factors have to be corrected for enhanced backscatter to the dose monitor as compared with the conventional block shieldings. METHODS: A method is presented to detect the monitor backscatter contributions to the output factor for irregular field settings. RESULTS: The monitor backscatter factors have been measured using a telescopic device for 2 different treatment head geometries (Varian Clinac 2100C/D, General Electric Saturne 15) and for 3 photon radiation qualities (nominal energies X6, X18, X12). A method is introduced to calculate the monitor backscatter for arbitrary irregular treatment fields from the experimental data for square or rectangular fields. CONCLUSIONS: Besides the corrections for changes in phantom scatter and changes in the aperture, corrections for monitor backscatter have to be taken into account in many clinical cases. They can contribute up to more than 10% compared with the monitor values for free regular fields.

Humans↗
PubMed1998

Radiation-induced optic neuropathy 4 years after radiation: report of a case followed up with MRI.

We report a case of radiation-induced optic neuropathy in a 32-year-old man with Cushing's disease and a recurrent tumour of the left cavernous sinus. The patient experienced rapid, painless loss of vision 4 years after treatment without recurrence of tumour or other visual disorder. MRI showed enlargement and contrast enhancement of the optic chiasm. A year later the patient was almost blind and MRI showed atrophy and persistent contrast enhancement of the chiasm.

Adenoma↗