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At least 775 records · Page 43Linked to original sources
PubMed1985

Thermal enhancement of the radiation damage in the mouse foot at different heat and radiation dose: influence of thermotolerance.

We studied the reaction of the mouse foot after combined X-irradiation and heat treatment. Acute reactions after heat differ from those after irradiation, however, after healing of the lesions, the same symptoms of deformity of the mouse foot remain. Prior heat treatment, 30 min at 43 degrees C, of the foot led to thermotolerance and this thermotolerance resulted in resistance to combined irradiation-heat treatments and hence to a decreased thermal enhancement of radiation effects. Resistance could be observed up to 168 h after prior heat treatment. The development of resistance to combined treatment at higher irradiation dose (15 or 20 Gy) and less severe heating was slower than at lower irradiation dose (10 Gy) and more severe heating. Thermal enhancement was confirmed to be dependent on the sequence of, and the interval between irradiation and heat treatment. When the mouse foot was made thermotolerant by prior heat treatment, thermal enhancement was always reduced, regardless of the sequence, when the combined heat and radiation treatments were given with an interval of less than 12 h. Thermotolerance led to an apparent decrease in the effective temperature employed in a combined treatment equivalent to approximately 1.0 degrees C, at temperatures above 43 degrees C in a 1 h heat treatment.

Animals↗
PubMed2006

Dose dependences of radiation induced yield in mixed radiation fields.

A theoretical model that describes dose dependences of trap filling (radiation yield) in mixed radiation fields consisting of two components is proposed. The model consists of one type of electron traps and one type of hole traps and assumes as an initial step the creation of two types of tracks, each represented by some volume with a uniform electron-hole pair density, different for each track. The relaxation process that follows comprises interband recombination, trapping of electrons and holes, and recombination of electrons with trapped holes and of holes with trapped electrons. These processes result in filled traps in amounts depending on the absorbed dose in the track and the number and types of tracks created in a given region of irradiated matter. The summation over the matter with areas of different degrees of overlapping (assuming poisson distribution of the created tracks), gives expressions for the dependences of trap filling as a function of doses for separated and simultaneous irradiation. It is shown that the key parameters determining the behaviour of the dose dependences are the ratios between the doses in the separated tracks and the average doses delivered on the irradiated matter by the separated components of the mixed field. If the ratios of the average dose to the track dose are low, the dose dependences will be linear. In the opposite limiting case the dose dependencies go to saturation. The linear and additive approximations of dose dependences in a mixed field are valid at low doses only.

Computer Simulation↗
PubMed2006

Influence of alpha and gamma radiations and non-radiation risk factors on the incidence of malignant liver tumors among Mayak PA workers.

This Mayak worker-based study focuses on evaluating possible associations between malignant liver cancers and chronic alpha irradiation, chronic gamma irradiation, and non-radiation risk factors (alcohol consumption, smoking, viral hepatitis, chemical exposure, and chronic digestive diseases). This is the first multivariate study related to liver cancer among Mayak workers. The study was performed using the nested, case-control approach and includes 44 cases of malignant liver tumors diagnosed from 1972 to 1999, and 111 matched controls. Adjusted odds ratio (OR(ad)) was evaluated relative to a group of workers with alpha radiation doses to liver (D(alpha)) < 2.0 Gy. Dose estimates of D(alpha) > 2.0 Gy (corresponding (239)Pu body burden estimates >20.4 kBq) were significantly associated (p < 0.003) with the occurrence of hemangiosarcomas (HAS) but only marginal significance (0.05 < p < 0.1) was found for hepatocellular cancers (HCC). The ORad for HAS was 41.7 [95% confidence interval (CI): 4.6, 333] for a group with D(alpha) in the range >2.0-5.0 Gy and was 62.5 (7.4, 500) for a group with D(alpha) > 5.0-16.9 Gy. The attributable risk (AR) was calculated as 82%. For HCC, O(Rad) was estimated as 8.4 (0.8, 85.3; p < 0.07) for a group with D(alpha) in the range >2.0-9.3 Gy. For the indicated group, the AR was 14%. An association with high external gamma-ray doses (D(gamma)) to the total body was revealed for both HCC and for combined liver cancers when dose was treated as a continuous variable. However, we find no evidence that chronic low doses of gamma rays are associated with liver cancer occurrence. Cholangiocarcinoma (CHC) was not associated with either alpha- or gamma-ray exposure. As expected, an association between alcohol abuse and HCC was inferred [O(Rad) = 3.3 (1.2, 9); AR = 41%] but not for CHC or HAS.

Alpha Particles↗
PubMedDate not supplied

Radiation pneumonitis in breast cancer patients treated with taxanes: does sequential radiation therapy lower the risk?

Taxanes are now routinely used in conjunction with radiation therapy (RT) as adjuvant therapy for breast cancer. Recent publications have reported several cases of radiation pneumonitis (RP) in patients receiving RT and taxane chemotherapy, thus raising concern as to the safety of this combination. To decrease the potential risk of RP, we sequenced RT after taxane chemotherapy with a target interval of 3-4 weeks in two consecutive institutional breast protocols. Forty patients were treated on two adjuvant systemic protocols consisting of modified radical mastectomy (n = 9) or breast-conserving surgery (n = 31), followed by adjuvant doxorubicin, cyclophosphamide, and a sequential taxane (ACT), followed by RT. All patients had either node-positive or high-risk node-negative breast cancer and were treated between October 2000 and September 2002. Postmastectomy, a median dose of 5040 cGy was delivered to the chest wall. After breast-conserving surgery, a median dose of 4680 cGy was delivered to the breast plus a 1400 cGy boost to the surgical cavity. Information regarding RP was gathered retrospectively by reviewing patient records. With a median follow-up of 28 months (range 6-42 months), no cases of clinical RP were identified and no local failures had occurred. The median time interval for all patients between the completion of chemotherapy and the initiation of RT was 34 days (range 5-70 days). At the latest follow-up, 2 patients were diagnosed with metastatic disease and 38 patients were without evidence of disease. Sequencing of RT after taxane therapy with a target interval of 3-4 weeks does not appear to result in increased pulmonary toxicity and is associated with good local control.

Adult↗
PubMed1990

Monitoring the radiation dose to a multiprogrammable pacemaker during radical radiation therapy: a case report.

Multiprogrammable pacemakers, using complimentary metaloxide semiconductor (CMOS) circuitry, may fail during radiation therapy. We report about a patient who received 6,400 cGy for unresectable carcinoma of the left lung. In supine treatment position, arms raised above the head, the pacemaker was outside the treated area by a margin of at least 1 cm, shielded by cerrobend blocking mounted on a tray. From thermoluminescent dosimeter (TLD) measurements, we estimate that the pacemaker received 620 cGy in scatter doses. Its function was monitored before, during, and after completion of radiation therapy. The pacemaker was functioning normally until the patient's death 5 months after completion of treatment. The relevant electrocardiograms (ECGs) are presented.

Aged↗
PubMed2006

Three dimensional radiation dosimetry in lung-equivalent regions by use of a radiation sensitive gel foam: proof of principle.

A polymer hydrogel foam is proposed as a potential three dimensional experimental dosimeter for radiation treatment verification in low-density tissue such as the lung. A gel foam is created by beating a radiation sensitive polymer gel mixture in an anoxic atmosphere. The mass density of the gel foam is in the order of 0.25-0.35 kg/dm3. Both nuclear magnetic resonance (NMR) spin-spin relaxation rate (R2) and magnetization transfer ratio (MTR) have been used to map the dose distribution from the gel dosimeter. It is found that MTR has significant advantages compared to R2 for mapping the dose distribution in the polymer gel foam dosimeters. The magnetization transfer ratio is found to be less dependent on the density and microstructure of the gel foam dosimeter while spin-spin relaxation dispersion has been observed making the spin-spin relaxation rate dependent on the interecho time interval. Optical microscopy reveals a microstructure that shows great similarity with human lung tissue. It is also shown how NMR hydrogen proton density measurements can be used to map the density distributions in gel dosimeters.

Dose-Response Relationship, Radiation↗
PubMed1992

Radiation-induced optic neuropathy: correlation of MR imaging and radiation dosimetry.

The authors performed topographic correlation of dosimetric measurements with contrast medium-enhanced magnetic resonance (MR) imaging signal aberration in two cases of radiation optic neuropathy. The region of pathologic contrast enhancement in the optic nerve and chiasm had received 55-62 Gy, which supports the theory that the risk of injury to the optic nerve and chiasm increases steeply with radiation doses above the tolerance level of 50-55 Gy.

Female↗
PubMed2006

Enhanced radiation sensitivity and radiation recall dermatitis (RRD) after hypericin therapy -- case report and review of literature.

BACKGROUND: Modern radiotherapy (RT) reduces the side effects at organ at risk. However, skin toxicity is still a major problem in many entities, especially head and neck cancer. Some substances like chemotherapy provide a risk of increased side effects or can induce a "recall phenomenon" imitating acute RT-reactions months after RT. Moreover, some phototoxic drugs seem to enhance side effects of radiotherapy while others do not. We report a case of "radiation recall dermatitis" (RRD) one year after RT as a result of taking hypericin (St. John's wort). CASE REPORT: A 65 year old man with completely resected squamous cell carcinoma of the epiglottis received an adjuvant locoregional RT up to a dose of 64.8 Gy. The patient took hypericin during and months after RT without informing the physician. During radiotherapy the patient developed unusual intensive skin reactions. Five months after RT the skin was completely bland at the first follow up. However, half a year later the patient presented erythema, but only within the area of previously irradiated skin. After local application of a steroid cream the symptoms diminished but returned after the end of steroid therapy. The anamnesis disclosed that the patient took hypericin because of depressive mood. We recommended to discontinue hypericin and the symptoms disappeared afterward. CONCLUSION: Several drugs are able to enhance skin toxicity of RT. Furthermore, the effect of RRD is well known especially for chemotherapy agents such as taxans. However, the underlying mechanisms are not known in detail so far. Moreover, it is unknown whether photosensitising drugs can also be considered to increase radiation sensitivity and whether a recall phenomenon is possible. The first report of a hypericin induced RRD and review of the literature are presented. In clinical practise many interactions between drugs and radiotherapy were not noticed and if registered not published. We recommend to ask especially for complementary or alternative drugs because patients tend to conceal such medication as harmless.

Aged↗
PubMed2002

New strategies for the prevention of radiation injury: possible implications for countering radiation hazards of long-term space travel.

New strategies for the prevention of radiation injuries are currently being explored with the ultimate aim of developing globally radioprotective, nontoxic pharmacologics. The prophylactic treatments under review encompass such diverse pharmacologic classes as novel immunomodulators, nutritional antioxidants, and cytokines. An immunomodulator that shows promise is 5-androstenediol (AED), a well-tolerated, long-acting androstene steroid with broad-spectrum radioprotective attributes that include not only protection against acute tissue injury, but also reduced susceptibility to infectious agents, as well as reduced rates of neoplastic transformation. Other potentially useful radioprotectants currently under study include the nutraceutical vitamin E and analogs, a chemically-engineered cytokine, interleukin-1beta, and a sustained-release formulation of an aminothiol, amifostine. Results suggest that a new paradigm is evolving for the prophylaxes of radiation injuries, based on use of newly identified, nontoxic, broad-spectrum prophylactic agents whose protective action may be leveraged by subsequent postexposure use of cytokines with organ-specific reparative functions.

Animals↗
PubMedDate not supplied

[Quantitative regularities for clinical manifestations of radiation injury in large-sized laboratory animals exposed to supralethal radiation doses Gamma-neutron and electron biological effectiveness as influenced by exposure conditions and dose distribution in the animal body].

The damaging effect of gamma-neutron radiation over a wide neutron-energy range, with average values of 0.37 and 1.2 MeV, and that of electrons with an average electron energy of 25 MeV have been compared in dogs and two monkey species exposed to a broad range of supralethal doses. An analysis of absorbed dose distribution in critical organs and systems has shown the highest effect of gamma-neutron radiation with an average neutron energy of 1.2 MeV. With severity of early clinical manifestations of damage as a criterion, electrons have appeared the most effective. The radiosensitivity of animals grew in the order as follows: dog-->M. fascicularis-->P. hamadryas.

Animals↗
PubMedDate not supplied

[The interactive determination of the mathematical model parameters for the planning of the radiation therapy of malignant tumors. 2. A method of adjusting the mathematical model parameters for calculating the tolerance doses and probabilities of the occurrence of radiation complications in body organs and tissues].

To enhance the accuracy of calculation of tolerance doses, adequate doses and the likelihood of radiation complications in normal organs and tissues, a method has been developed for local model parameter adjustment (LMPA) by using mathematical models. It includes the analysis of the structure of a mathematical model, the systematization of clinical data and their goal-oriented use for model adjustment. The necessity of developing a new research line (LMPA) is determined by the complexity of the irradiated organism as a system and by the attempts to take into account the impact of the system on the parameters of mathematical models. LMPA can be considered to generalize determination of the parameters of mathematical models or their directed (interactive) determination. The strategy of using LMPA, which is based on the preset radiation treatment protocol and its respective dosage distributions in normal organs and tissues, is described. The efficiency of LMPA is shown to depend on the volume and relevance of clinical data that the radiological therapist has at his disposal.

Computer Simulation↗
PubMedDate not supplied

[Radiation detectors and the problem of radiation loads in roentgenodiagnosis].

The development of new effective roentgenolumonophors, screens, based thereon, and image intensifiers helps reduce the exposure radiation dose in radiography, fluorscopy and fluorography. The effect produced by the characteristics of diverse elements of the radiation dectector on the increase of sensitivity is considered. Numerical values of some characteristics are cited.

Fluoroscopy↗
PubMed1992

[Dynamics of the radiation conditions and evaluation of the radiation dosage of the inhabitants of Kiev following the accident at the Chernobyl Atomic Electric Power Station].

The estimation of the effective dose equivalents of exposure to accidental and non-accidental sources was made on the basis of the studying of radiation situation variations in Kiev after the Chernobyl accident in 1986-1989. The total annual effective dose equivalents to the Kiev population from all sources of exposure for 1986-1989 were 9.19, 7.29, 5.34 and 5.03 mSv, respectively. The necessity of radiation health measures aimed at limiting the intake of long-acting radionuclides of Chernobyl nature and reducing the exposure doses by optimizing the x-ray procedure and by regulating the natural radioactivity of building materials are under discussion.

Accidents↗
PubMed1989

[Polymer materials for biomedical use obtained by radiation methods. III. Radiation cross-linking of acrylamide and N-vinylpyrrolidone].

The course of the radiation formation of hydrogels in aqueous solutions of acrylamide and N-vinylpyrrolidone was investigated on the base of gel-sol analysis. Using relations from Inokuti's equation as a test of crosslinking mechanism it was pointed out that creation of gels takes place according to classical mechanism e.g. through four-functional joining points. In the systems containing oxygen gel formation results from simultaneous crosslinking and degradation. On the base of swelling measurements of gels (ROCH method) the yields of radiation processes were calculated. Using a method of pulse radiolysis the absorption spectra of macroradicals were recorded, their structures discussed and the rate constants of crosslinking estimated.

Acrylamides↗
PubMedDate not supplied

[The equivalent dose as a dosimetric criterion of acute radiation injury by radiations of various quality. Energy dependence of generalized coefficients of the quality of neutrons].

The notion of "a generalized equivalent dose" was introduced in order to use an equivalent dose as a dosimetric criterion for the estimation of acute exposure to densely ionizing radiation. The generalized quality coefficients that were used to quantify a generalized equivalent dose depended on LET, and with gamma/neutron radiation, on neutron energy. Several possible LET functions of the generalized quality coefficients were chosen and mean quality coefficients were transformed, depending on neutron energy, and estimated for actual neutron energy distributions, used in radiobiological experiments, with due regard for the alteration in the neutron spectrum with the body depth.

Animals↗
PubMed1987

[Radiation exposure and radiation risk in our environment].

The extent of radiation exposure of the population of central Europe will be described by natural sources, by medical application and exposure by nuclear power facilities with special emphasis of the accident in Chernobyl. It will be shown, how the assessment of the various exposures can be standardized. Especially the risk for cancer and genetic diseases should be taken into account. The consequences for optimal radiation protection will be discussed.

Accidents↗
PubMed1985

[Escherichia coli K-12 mutants with increased resistance to ionizing radiation. V. The effect of mutations on spontaneous and radiation mutagenesis].

The frequencies of spontaneous mutations (reversions his-4----His+ and forward mutations to rifampicin-, nalidixic acid- or valine-resistance) in radiation-resistant mutants Gamr444 and Gamr445 are much lower than in the wild-type strain AB1157. His+ revertants and rifampicin-resistant mutants Rifr are induced by low doses of gamma-rays more efficiently than in the wild-type. Low doses of UV light only enhanced mutagenic activity in Gamr strains for induction of His+ reversions but not for Rifr mutations. For the wild-type strain the frequencies of His+ and Rifr mutations increase proportionally to the square of dose both of UV light and gamma-rays. For the most radioresistant Gamr444 mutant the frequencies of UV- and gamma-rays-induced Rifr mutations and of gamma-rays-induced reversions increase linearly with the dose. Possible reasons for these anomalies of radiation-induced mutagenesis in Gamr mutants are discussed.

DNA Repair↗
PubMedDate not supplied

[Determination of the contribution of gamma radiation to absorbed dose and the radiobiological effects in the radiation field resulting from the reaction p(50MeV)--Be].

A contribution of gamma-radiation to a total dose absorbed in the radiation field formed during 50 MeV proton bombardment of a beryllium target has been determined. A study was made of the biological effectiveness of action of mixed gamma/neutron-radiation on albino mongrel and inbred (C57 black) female mice.

Animals↗