International Journal of Radiation Research
Volume:13 Issue: 2, Apr 2015

It is now universally accepted that DNA is the main target for damages caused by physical and chemical genotoxicants. Although there are different methods to measure directly the induced DNA damages but due to fast repair processes in cellular environment, most of the damages would be repaired even before sampling, therefore processed DNA damages, i.e. damages left unrepaired after acting repair machinery is preferable to measure in various exposure scenarios. Various cytogenetic end points are introduced and implemented such as metaphase analysis, sister chromatid exchanges, premature chromosome condensation, translocation assay and micronucleus assay. All of these methods were extensively used for various purposes but among them micronucleus (MN) assay was found more practical because of ease of scoring, potential for automation as well as being nearly as sensitive as other procedures. These characteristics made MN assay very popular for screening of the effects of various genotoxic agents in vitro and in vivo. In this review we try to summarize the main aspects of application of this method in radiobiological studies and genome instability related diseases.

The present work aims to study the out-of-field photon calculation accuracy of a commercial treatment planning system (TPS), Oncentra, for three-dimensional conformal radiotherapy (3D-CRT) and intensity modulated radiation therapy (IMRT) treatment techniques from Elekta Synergy medical linear accelerator. Accuracy of individual out-of-field dose components was studied by defining a square field of 10 x 10 cm2 in our TPS and it is verified by using ionization chamber and TLDs (Thermoluminescent dosimeter) at 5 cm depth. Using 3D-CRT and IMRT techniques Ca (carcinoma) prostate treatment plans were created using 6 MV photon beam and calculated in Oncentra Masterplan v4.3 planning systems for out-of-field and further compared the same with TLD measurements. Individual components study shows the poor out-of-field calculations in TPS, with respect to that obtained from TLD measurements. Underestimation increases from 10 % to 80 % as a contribution from various components while moving far from field edge. Complex IMRT plans resemble this underestimation of TPS calculations in greater extend. This study quantifies the poor accuracy for out-of-field dose calculations in TPS. No significant difference in 3D-CRT and IMRT plans is found at near field edge. While, as distance from field edge increases, underestimation of TPS in IMRT plan is higher. 10 % – 60 % difference in out-of-field dose was found as distance move from 2 cm to 7.5 cm far from field edge between TPS estimations and the measurements.

The concentrations and distributions of natural and anthropogenic radioactive materials in soils of the site of Rooppur Nuclear Power Plant (RNPP) were investigated with the aim of evaluating the environmental radioactivity and radiation hazard. Soil samples were collected from 40 locations in and around the proposed site of Rooppur Power Plant and determined the activity level by using a gamma-ray spectrometry. The concentrations of 226Ra, 232Th, and 40K in soil samples, radium equivalent activity (Raeq) for soil, absorbed dose rates, external hazard (Hex) values were determined. No artificial radioactivity (137Cs) was found in these samples. This present study provides a baseline of radioactivity and radiation levels in the proposed nuclear power plant site area at Rooppur. It will be utilized to correlate the radioactivity measured after operation of the reactor.

Vegetation (food stuff) is grown in soil that contains many radioactive elements such as 238U (uranium), 232Th (thorium) and 40K (potassium), which may get deposited either due to radioactive fallout or/and by absorption from the soil and can pose serious health hazards. Natural radioactivity, radiological hazards and annual effective dose assessment was carried out in vegetation samples (vegetables, cereals and fruits) collected from fields and market. Gamma spectrometry using HPGe detector was used. The measured specific activity concentration of 238U (uranium), 232Th (thorium) and 40K (potassium) varied from 10.25 ± 0.94 Bq/kg to 29.13 ± 0.69 Bq/kg, 22.20 ± 2.46 Bq/kg to 58.21 ± 1.15 Bq/kg, and 1158.4 ± 26.05 Bq/kg to 1962.2 ± 18.17 Bq/kg respectively in various vegetable and cereal samples and varied from 2.5 ± 0.16 Bq/kg to 9.8 ± 0.15 Bq/kg, 7.4 ± 1.24 Bq/kg to 18.4 ± 1.39 Bq/kg, and 287.13 ± 11.23 Bq/kg to 815.72 ± 12.50 Bq/kg respectively in various fruit samples studied in the present work. From these values, hazard indices, the minimum and maximum values of absorbed dose and indoor and outdoor annual effective doses were calculated for various samples used in the present investigation. The various values obtained were found to be within the recommended limits. The absorbed dose and annual effective dose for the vegetable and cereal samples in which fertilizers were used to enhance the crop yield were higher than that in fruit samples.

Radio-adaptive response and bystander effects are known phenomena occurring in cells following exposure to ionizing radiation (IR). In this study we examined possible radio-adaptation of lymphocytes following bystander effects induced by CHO-K1 cells. Whole blood and CHO-K1 cells were cultured in RPMI-1640 complete medium. Cells were separately irradiated with various doses of gamma rays. A co-culture was set to examine the bystander effects induced by CHO-K1 cells on lymphocytes exposed later to a challenge dose of 4 Gy. Treated cells were exposed to cytochalasin-B to arrest cells in cytokinesis stage. Micronucleus (MN) as end point was scored in binucleate cells after staining in Giemsa. The frequency of MN increased significantly with increasing dose of radiation both in lymphocytes and CHO-K1 cells (p<0.001). Although, no significant difference was observed between control non-irradiated cells and those exposed to 0.2 Gy (p>0.05). Co-culture of the non-irradiated lymphocytes with pre-irradiated CHO-K1 cells significantly reduced the mean frequency of MN in lymphocytes irradiated with a dose of 4Gy (p<0.001). Results showed that bystander effects induced by gamma-irradiated CHO-K1 cells led to induction of radio-adaptive response in lymphocytes. The mechanism by which radio-adaptive response is induced following bystander effect is not clearly known, however cellular signaling and genome instability induced in cells indirectly might be considered as possible triggering events for radio-adaptive response.

Ionizing radiation causes cognitive impairment in adult brain. However, the effects of various irradiation protocols with fractionated fixed total dose on hippocampal function have not yet been studied. Fractionated whole brain irradiation with a total dose of 36 Gy was performed according to the following protocols: 2Gy-18 fractions (2Gy*18), 4Gy-9 fraction (4Gy*9) and 6Gy-6 fractions (6Gy*6). Changes in spatial memory were studied in Morris water maze tests at 12th and 17th day after irradiation with a hidden platform and at 38th day after irradiation without a platform. Levels of expression of brain derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) genes were evaluated using qPCR. Expression of genes of neurotrophic factors (BDNF and VEGF) was decreased at 4th and 8th week after irradiation, the decrease depended on fractionation. The Morris water maze test with a hidden platform showed improvement in long-term spatial memory at 12th and 17th day after irradiation. In the Morris water maze test without platform cognitive deficit was detected only in 6Gy*6 group at 4th week after irradiation. Our study shows that different fractionation protocols affect hippocampal functions differently, and that the greatest negative impact has the protocol with the maximum single dose. In addition, decrease in expression of genes of neurotrophic factors might play an important role in cognitive impairment.

In the current study the effect of shielded colpostat on rectum received dose was calculated in cervical brachytherapy using Monte Carlo (MC) method. Two 60Co sources of GZP6 brachytherapy unit used for intracavitary treatments were simulated using MCNPX Monte Carlo code. Also the two types of colpostats including shielded and unshielded were simulated inside a water phantom. The radial dose function, depth doses and dose distribution around sources were calculated with spatial dose resolution of 2×2×2 mm. The effect of tungsten shields on rectum dose was studied. Moreover, the accuracy of treatment planning system (TPS) was verified comparing to MC results. Our results showed that shielded colpostats reduce the rectum dose up to 7% according to the MC calculations. Also, it was found less than 3% difference between TPS and MC results in percentage depth dose and radial doses for unshielded case. It can be concluded that the application of shielded colpostats provide a relatively mild protection (7% reduction in dose) for the rectum in intracavitary brachytherapy due to the higher energy of 60Co photons. However, application of shielded colpostats in treatment planning system is desirable for more accurate treatments.

Therapeutic radiopharmaceuticals are designed to deliver high doses of radiation to selected target organs with an aim of minimizing unwanted radiation to surrounding healthy tissue. Due to the potential of targeted radiotherapy to treat a wide range of malignant conditions, [153Sm]-samarium maltolate was developed for possible therapeutic applications. The organ radiation-absorbed doses have been evaluated for human based on animal data. After intravenous administration of 153Sm-Mal to four groups of rats, they were sacrificed at exact time intervals and the percentage of injected dose per gram of each organ was calculated by direct counting from rat data. Then S values for 153Sm by using specific absorbed fractions were calculated. By taking advantage of the formulation that Medical Internal Radiation Dose suggests, radiation-absorbed doses for all organs were calculated and extrapolated from rat to human. From rat data, it is estimated that a 185-MBq injection of 153Sm-Mal into a human might result in the highest absorbed dose in the lymphoma tissues (liver 176.3, lungs 68, spleen 66.8 and sternum 19 mGy), especially in liver respect to the other tissues. These results suggest 153Sm-Mal as an efficiently new therapeutic agent in order to overcome possible lymphatic malignancies.

Radiation-induced bystander effect is a response which results in damage in non-irradiated cells in response to signals from the irradiated cells. The aim of the present study was to investigate microwave-induced bystander effect from a GSM mobile phone simulator on induction of apoptosis in Jurkat cell line. Jurkat cells were divided into three groups of non-irradiated, exposed and bystander (medium transfer from the irradiated cells). The exposed group was subjected to irradiation from GSM mobile simulator for 2h and 12h; the medium from irradiated cells was then transferred to the bystander cells. Apoptosis rate was measured12 and 24 hours after treatment by Annex in V 7-AAD kit using flow cytometry. Apoptosis was observed in both exposed and bystander cells of Jurkat cell line. The difference among non-irradiated, exposed and bystander cell groups was significant (p<0.05). From the obtained results it can be concluded that microwave radiation exposure in Jurkat cells leads to a significant increase in the apoptosis rate not only in the exposed cells but also in the bystander cells.

Seaweeds contain significant quantities of lipids, protein, vitamins and minerals. Aquavac Ergosan contains 1% alginic acid extracted from two brown seaweeds, Laminaria digitata and Ascophyllum nodosum. Both in vivo and in-vitro researches have mainly been focused on the effect of Ergosan on fish growth, survival rate, reproductive performance and innate immunity in blood and epidermal mucus. Despite numerous studies on the effects of Ergosan on immune system of aquatic animals and evaluation of seaweeds in proximate analysis, there is no data available on proximate analysis of irradiated Ergosan extract (alginic acid). Therefore, the aim of this study was to assess the effect of on different groups of irradiated alginic acid (10, 20, 30, 40 and 50 KGy) for analyzing proximate composition. Alginic acid was prepared from the sonicated Ergosan extract. The Alginic acid extracted from Ergosan was irradiated with a gamma cell. The protein and lipid content and Moisture and ash were recorded. Statistical analysis showed no significant differences among all of groups in terms of protein, lipid, ash and moisture. Radiation processing is a very convenient tool for imparting desirable effects in polymeric materials. The polysaccharide degradation by gamma or ultraviolet irradiation is free of initiators. High energy radiation technique can be effectively used to decrease the molecular weight of different polysaccharides such as alginate and Chitosan. Based on the results of this study, gamma irradiation of alginic acid as natural polysaccharide had no effect on crude protein, crude lipid, moisture and ash.

In order to deliver the precise dose to the target in radiotherapy, absorbed dose to water at the reference point should be assessed. When the calibration procedure is performed for a reference dosimeter in the 60Co beam of a Secondary Standard Dosimetry Laboratory (SSDL), the total uncertainty in absorbed dose to water (Dw) is estimated to be approximately 1.5%. This study attempts to re-measure the ND,W factors for all available field chambers at Reza Radiotherapy & Oncology Centre (RROC). Consistency and linearity checks were performed for a range of available chambers using a check source. The ND,W factors were also measured for the ionization chambers. All cylindrical chambers have been cross calibrated at 6 MV photon beam using a Siemens Primus Plus Linac. The Plane Parallel Chamber has been cross calibrated at the highest available electron beam and the ND,W factor has been measured. The tolerance of consistency and linearity checks has been reported to be within 0.3%. The ND,W value for field Farmer chamber was found in agreement with certificate within 1%. In contrast for small active volume chambers, the deviation from the SSDL reports was 2.3%. For the plane parallel chamber, the difference between SSDL and Home measurements are found to be 12%. Although the calibration of reference chambers used for absolute dosimetry through a Primary Standard Dosimetry Laboratory (PSDL) or SSDL is recommended, for field chambers this can be done at home department as a Tertiary Standard Dosimetry Laboratory (TSDL).

The Shielding methods in radiotherapy due to delivering an accurate radiation dose to cancer tissues and avoiding unnecessary dose to normal tissues are very important. These methods include Lead standard blocks, individual molding and multi leaf collimator (MLC). The MLC method is not still common in Iran radiotherapy centers. Individual molding is better than the lead block shielding because of lower operator error and time consuming. This study was performed in Shahid Ramazanzade radiotherapy center of Yazd and intended to compare radiation dose due to the two shielding methods of lead and Cerrobend. The radiation field sizes of head and neck, pelvis, and breast cancer treated by Cobalt unit, 9MV, and 6MV photon beams of Neptun and Compact linear accelerators were studied, respectively. The Absolute and Relative dosimetry were achieved by Farmer ionic chamber and diod detector. The Absolute and Relative dose values which were measured at the two shielding methods of lead standard and Cerrobend individual molding were similar without significantly difference. The miss difference dose between these two methods shielding and the advantages such as saving time, precision, and accuracy lead to preference of individual molding method rather than the lead block shielding.