International Journal of Radiation Research
Year:2003 | Volume:1 | Issue:1|Papers Count:9

The rapid discoveries of X-rays by Roentgen, natural radioactivity by Becquerel and radium by Curies at the end of 19th century changed broadly the worlds of physics, biology and medicine. At the close of the 20th century, fundamental discoveries in biology at moecular level, often appear to overshadow this earlier work. However as more basic discoveries are made these separate scientific eras merged to contribute to the conquest of disease, specially cancer. The rapid advancements achieved during recent years, mainly due to revolutionary methodological improvements, have led to an unparalleled explosion of information. The exponential growth of data so impressive that the conceptual evaluation of the material has seemed almost an insignificant part of the scientific process. All these achievements have allowed researchers to ask new questions or to rephrase old ones. The result is a virtual avalanche of new formed knowledge.

This article provides a brief review of aspects of biophysical modelling in radiation biology. A major concern of radiation biology in the past half century has been the quantification of the health hazards of ionising radiations of different qualities and extrapolation of human cancer risks at high dose and dose rates to low dose and dose rates (UNSCEAR 1993). In the past decade with the accelerated progress in molecular biology techniques and advances in theoretical methods attention has become more focused on mechanistic studies and interpretation of effects of ionising radiation. To this end, track structure has provided a theoretical tool to investigate those parameters of ionising radiation that predominantly determine the nature and magnitude of the final effect (Vogelstein and Kinzler 1998).

Background: Recent results have provided increasing evidence to support involvement of membrane damage in the mechanism of ionizing radiation induced killing of mammalian cells. These findings have stimulated renewed interest in evaluating the damage to membrane as a primary initiator in radiation-induced cell killing especially in apoptotic death. The present study was aimed to gain deeper insight on the molecular mechanisms of radiation-induced damage at membrane level with consequences to apoptotic cell death. Materials and Methods: Radiation mediated changes in membrane fluidity in egg yolk lecithin (EYL) liposomal membrane were studied by employing 1,6-diphenyl hexatriene (DPH) fluorescence polarization and subsequent oxidative damage by measurement of malondialdehyde (MDA) by thiobarituric acid reactive species (TBARS) spectrophotometrically. Alterations in membrane permeability and nuclear dimensions in g -irradiated immature mouse thymocytes were investigated by fluorescein diacetate (FDA) and propidium iodide (PI) method, respectively.Results: Results on irradiated liposomes have shown dose dependent lipid peroxidation with concomitant alterations in bilayer fluidity. These parameters were found significantly modified, when liposomes were prepared with a -tocopherol or cholesterol suggesting the contributions of both the radical scavenging and matrix modifying factors in membrane peroxidative damage. In addition, studies on mouse thymocytes labeled with FDA and PI have shown increased permeability of the plasma membrane and decreased nuclear diameter following g -irradiation of thymocytes. Alteration in membrane permeability with the time of post-irradiation incubation was found correlated with the induction of apoptotic death of thymocytes.Conclusion: These results suggest that membrane associated radiation damage were correlated with changes in the nucleus of cells. Moreover, the membrane damage seems a primary trigger in radiation-induced apoptosis which may have implications in cancer radiotherapy. Iran. J. Radiat. Res.;

Background: A powerful and improved technique, Proton Induced X-ray Emission (PIXE) has been performed-yielding the elemental composition of 17 samples of surgically excised malignant and normal tumors of breast tissue. The samples without any further process as thick targets were put on capton foil backing. There are no homogenizing processes. The PIXE spectra analysis was performed using he non-linear least square fitting code AXIL and GUPIX. Materials and Methods: The samples are taken from patients in the wide range of age and are bombarded by 2.0 Me v energy proton beams produced by van de graff accelerator in vacuum. The quantitative comparison between two types of tissues was evaluated by assessing the presence of c alcium, Potassium, Iron, Copper and Zinc, as minor and trace elements. Results: Results in this study indicate that relative values of Cu / Zn, P / K and also Ca and S in benign type were higher than those in malignant type, but the concentration of Fe and Zn in cancerous tissues was significantly higher than those for benign type. Conclusion: Results suggest significant elevation of Zinc in the pathological tissues. Cu/Zn ratio for both type of tissues are evaluated. The results show that this ratio in patients with breast cancer is significantly lower than the normal group. Selenium and Arsenic was not obtained in any of 17 samples. Most of the tissues of benign kind (Fibrocystic and Fibro adenoma) contain Cadmium.Calcium concentration in normal tissues is significantly higher than tumorous tissues. Iran . J. Radiat. Res., 2003; 1(1): 23 - 27

Background: Previous investigations have revealed, cimetidine, a histamine H2-receptor antagonist, show radioprotective effects against gamma- and neutron-induced micronuclei in bone marrow erythrocytes. In this study, the anticlastogenic effects of famotidine and ranitidine, which act similar to cimetidine as histamine H2-receptor antagonists, was investigated. Materials and Methods : Balb/c male mice were injected i.p. with various doses of famotidine and ranitidine two hours before 2 Gy gamma irradiation. Frequency of micronuclei was determined in bone marrow erythrocytes following each treatment. Results: The results indicated that gamma irradiation alone can cause a high frequency of micronuclei formation and decrease cell proliferation ratio. Pre-irradiation injection of famotidine and ranitidine, of various doses, effectively reduced the number of micronucleated polychromatic erythrocytes (MnPCEs), yet has no effect on cell proliferation ratio (PCEs/PCEs+NCEs). In fact, these two drugs reduce the clastogenic effects of gamma rays, while they are ineffective against the cytotoxic properties of gamma rays. Conclusion: The dose reduction factor (DRF) calculated, shows a DRF=2 for famotidine and a DRF=1.8 for ranitidine which is indicative of a high radioprotective property of these drugs. The mechanism in which these drugs reduce clastogenic effect of gamma radiation is not fully understood. It might be due to their antioxidant and free radical-scavenging properties. Iran

Backgrounds: Bleomycin (BLM) has been labeled with radioisotopes and widely used in therapy and diagnosis. In this study BLM was labeled with [62Zn] zinc chloride for oncologic PET studies. Materials and methods: The complex was obtained at the pH=2 in normal saline at 90 ° C in 60 min. Radio-TLC showed an overall radiochemical yield of 95-97% (radiochemical purity > 97%). Stability of complex was checked in vitro in mice and human plasma/urine. Results: Preliminary in vivo studies performed to determine complex stability and distribution of [62Zn] BLM in normal and fibrosarcoma-bearing mice. [62Zn] BLM accumulated significantly in induced fibrosarcoma tumors in mice according to bio-distribution/imaging studies. Conclusion: [62Zn] BLM can be used in PET oncology studies due to its suitable physico-chemical properties as a diagnostic complex in vitro and in vivo. Further studies should be performed for evaluation of the complex behavior in higher animals

Background: Since 1984 MRI gel dosimetry has been introduced as a potential technique for 3D dosimetry. Most of the studies have measured R1 (1/T1) or R2 (1/T2) properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Methods: Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques.Results: Our results showed that linear response exists between the variations of image intensity with absorbed dose (1-15 Gy). Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo (GRE) imaging technique also have been studied in comparison with classic spin echo (SE) imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel dosimetry. Reduction of imaging time is achievable in image intensity technique so that it’s possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel. Iran

Backgrounds: Thallium-201 is produced through 203Tl (p, 3n) 201pb 201Tl reaction by cyclotron. This radioisotope has known as one of the cyclotron radioisotopes which is used for myocardial perfusion in the coronary artery disease, Tl-201 after chemical purification and quality control in the form of 201Tl-chlorid is ready to send to the hospitals. Materials and methods: In this work the effect of the proton energy on quality of Tl-201, was studied. Radionucleidic purity was determined by high purity Ge (HPGe) detector Gamma spectrometer, in production time and after one half-life (73h). The targets were coated with Enriched Thallium-203 (97%). Results: The Variation of thickness of targets was 18.3 ± 1.3µm. The different energies of bombardment on quality of Tl-201 and Tl-200, Tl-202, and Pb-203 (as impurity) were studied. The results have shown that optimum energy for proton was 28.5 MeV. Conclusion: The variation energy of bombardment can change the purity of Tl-201 but all results were in the standard range according to the United States Pharmacopoeia (USP) and European Pharmacopoeia.

Background : There are growing evidences for chromosomal radioadaptive response in human lymphocytes . Highly variable inter- and intra-individual responses have been reported. Some individuals are non-responders and even in some donors the frequency of chromatid aberrations induced by a challenge dose increases by pre-exposure to an adapting dose. It has been proposed that the lack of radioadaptive response is due to transient physiological factors. Materials and Methods : We found a young healthy donor who exhibited no radioadaptive response in our initial experiments. After a common adapting dose, the donor occasionally showed a highly increased susceptibility to subsequent high-dose irradiation. To assess whether the lack of radioadaptive response and the induction of a synergistic effect are transient responses , we have performed a 3-year follow-up study employing micronuclei in binucleated cells besides chromatid aberrations as biological endpoints. To eliminate the effect of the cell cycle on intrinsic radiosensitivity of a cell, we used the multiple-fixation regimen for analysis of chromosomal aberrations. Results : This donor showed no adaptive response in any experiment.Conclusion : Considering the consistent non-responsiveness observed throughout our serial experiments, it may be concluded that the lack of radioadaptive response is not attributed to some transient physiological factors but rather to permanent constitutional traits