International Journal of Radiation Research
Volume:9 Issue: 2, Apr 2011

All living organisms are exposed to ionizing radiation comprising cosmic rays coming from outer space, terrestrial nuclides occurring in the earth’s crust, building materials, air, water and foods and in the human body itself. The exposures are constant and uniform for all individuals everywhere including the dose from ingestion of 40K in food. Cosmic rays are, more intense at higher altitudes, and the levels of uranium and thorium in soils are elevated in localized areas. Exposures also vary as a result of human activities and practices. In particular, building materials of houses and the design and ventilation systems strongly influences the indoor levels of the radioactive gas radon and its decay products, which contributes the doses through inhalation. Component of the sources of exposures to Indian population has been assessed based on the data generated. Total contribution from the natural sources to the Indian population works out to 2.3 mSv/y as against the global value of 2.4 mSv/y. Estimated modified source including mining of heavy metals, coal fired power plants, mining of phosphate rocks and its use as fertilizers, production of natural gas, gas mantles and luminescent dial and air travel contribution to the background radiation to the Indian population works out to be 1.2 x 10-3 mSv/y; atmospheric weapon tests contributes about 0.045 mSv/y, medical exposure contributes about 0.048 mSv/y and exposure due to nuclear power production contributes about 5.0 x 10-5 mSv/y to the background radiation. Brief review and comparison of the dose rates arising from natural and man made sources to the Indian population is given.

Health hazards associated with exposure due to the natural radioactivity which is a part of our physical environment are of great concern. In order to assess the risks associated with exposure due to the natural radioactivity in soil and building materials, extensive studies have been carried out all over the world. The most commonly encountered radionuclide’s are 238U, 232Th, their decay products and 40K. In order to study the concentration of these radionuclides soil, sand, gravel aggregates, bricks and marble, samples were collected from different sites and local suppliers of the district Mirpur, Azad Kashmir (Pakistan). 226Ra, 232Th, and 40K activities in the collected samples were measured using HPGe detector. The measured specific radioactivity concentration of 226Ra, 232Th and 40K in the studied samples ranged from 10 ±1 to 47 ± 2, 18 ± 1 to 75 ± 4 and 40 ± 3 to 683 ±3 Bq.kg-1, respectively. From the measured activity concentration, radium equivalent activity, external and internal hazard indices, gamma and alpha indices, terrestrial absorbed dose and annual effective dose were calculated. Maximum value of radium equivalent activity of 197.1 ± 9 Bq.kg-1 was observed in soil sample whereas minimum value of 45.9 ± 2 Bq.kg-1 was found in gravel aggregates. Relatively higher mean values of hazard indices were found in brick samples. Annual effective dose varied from 0.06 ± 0.01 to 0.47 ± 0.02 mSv.y-1. Current values of annual effective dose, radium equivalent activity and hazard indices have been found to be within the recommended limits.

The exposure of human being to ionize radiation from natural sources is a continuing, inescapable feature of life on earth. Direct measurement of absorbed dose rates in air has been carried out in many countries of the world during the last few decades. Such investigations can be useful for assessment of public dose rates, the performance of epidemiological studies, and keeping reference-data records to ascertain possible changes in the environmental radioactivity duo to nuclear, industrial, and other human activities. The measurements of the outdoor and indoor- environmental exposures including cosmic and terrestrial components were accomplished by a portable Geiger Muller detector (RDS -110). The measurements were made during daylight from September to October 2009, in five areas within nine big cities of Lorestan province. In each area, one building was randomly selected for indoor and outdoor measurements. Measurements were made for each region and an average value was used to calculate the exposure rate from gamma background radiation. The results showed the Maximum and minimum outdoor dose rates as 166±44 and 65±8 nSvh-1 in Borujerd and Pol-e- dokhtar, respectively. The average of outdoor dose rates was determined 113±26 nSvh-1. Also the maximum and minimum values of indoor dose were 157±52 and 74±14 nSvh-1 in Borujerd and Pol-e-dokhtar, respectively. The average indoor dose rates were determined as 119±27 nSvh-1. The average annual effective dose for gamma background radiation in Lorestan province has been 0.72 mSv, with the range of 0.3– 0.6 mSv which was more than the global value (0.48 mSv). A poor correlation coefficient between was observed altitude and absorbed dose rates.

The Poly-Allyl Diglycol Carbonate (PADC) detector is of particular interest for development of a fast neutron dosimeter. Fast neutrons interact with the constituents of the CR-39 detector and produce H, C and O recoils, as well as (n, α) reaction. These neutron- induced charged particles contribute towards the response of CR-39 detectors. Electrochemical etching was used to enlarge track diameter which was made by low energy recoil protons. Before electrochemical etching, a chemical etching was performed for 1 hour. The responses were also calculated by Monte Carlo simulations, using MCNPX code in different energy bins considering H, C and O recoils. The total registered efficiency and partial contributions of the efficiency, due to interactions with each constituent of CR-39, were calculated. The optimized condition of etchant was obtained to be 6N KOH 15kV.cm-1, and 6 hours etching time. The obtained results show that track efficiency of CR-39 was a function of incident neutron energy. The tracks caused by O and C recoil nuclei were negligible for neutron energies lower than 1 MeV. At neutron energies lower than 1 MeV, only recoil protons would have sufficient energy to leave visible tracks. But, O and C recoils had important contributions in overall response of PADC at neutron energies of few MeV. The efficiency of a CR-39 based dosemeter could be calculated by MCNPX code and the results were in a good agreement with experimental results in energy range of 241Am – Be bare source and 241Am-Be was softened with a spherical polyethylene moderator of radius of 20 cm.

The formalism recommended by Task Group 60 (TG-60) of the American Association of Physicists in Medicine (AAPM) is applicable for β sources. Radioactive biocompatible and biodegradable 153Sm glass seed without encapsulation is a β- emitter with a short half life and delivers a high dose rate to the tumor in the millimeter range. In this work the dosimetry parameters of the seed for brachytherapy were evaluated. Using MCNP4C code data, the Dosimetric parameters of AAPM TG-60 recommendations including the reference dose rate, the radial dose function and the anisotropy function were obtained. Two dimensional dose distributions were also calculated. The dose rate at reference point was estimated to be 9.41 cGy.h-1.μCi-1 for 153Sm. 153Sm with its relatively low energy beta component falls off the most rapidly of the other beta emitters. The calculated data was compared with that of several beta and photon emitting seeds. The results showed the advantage of the beta emitting 153Sm source in comparison with the other beta emitting sources, Because of its rapid dose fall-off of beta-ray and high dose rate at the short distances of the seed. The results would be helpful in development of the radioactive implants using 153Sm seeds for the brachytherapy treatment.

The heterogeneous composition of the human body presents numerous tissue types and cavities with widely differing radiologic properties. The aim of the present work was to develop a low cost homogeneous and heterogeneous phantom and the absorbed dose were measured by ionization chamber for different radiotherapy treatment techniques and compared with treatment planning system absorbed dose values. Present work deals with the fabrication of inexpensive homogeneous and heterogeneous tissue equivalent slab phantom using polymethyl methacrylate, cork, teflon and perspex as a tissue, lung, spine and tumor simulating materials respectively. These phantoms were used for different treatment techniques and full rotation techniques in SSD and SAD techniques. The measured dose values for the different positions of both phantoms were compared with the TPS values. The values are coinciding with each other and the percentage of deviation varies from 0.47 to 2.8 and 0.49 to 2.86 for heterogeneous and homogeneous phantoms respectively. The measured values from ion chamber were compared with 3-D Plato Treatment Planning System (TPS). TPS values were also revealed the same result for homogeneous and heterogeneous phantoms. The dose value of tumor is found to be gradually decreased with increase in arc angle. The dose value of spine is also found to be gradually decreased up to 90° and increased in 360°. Heterogeneity correction would definitely improve the cancer treatment of the heterogeneity region. This in-house phantom is inexpensive, easy to handle and very useful one to verify the TPS calculation.

Tangential irradiation of intact breast is one of the most common procedures performed in any radiotherapy center. This method is performed by using 2D and 3D treatment planning. The aim of this study was to compare 2D with 3D plans in breast conserving radiotherapy. Homogeneity of isodose, and lung received dose were compared. Twenty patients with breast cancer undergoing lumpectomy were included in this study. Two dosimetry plans were generated for each patient. The first plan was performed on one CT-slice (central) by using Eclipse-TPS. The second plan was based on full CT-slices using the same TPS. For both plans, the volumes receiving lower than 95% (cold areas), greater than 105% (hot areas) of the reference dose and the volume of lung receiving ≥30Gy (Vol≥30Gy) were derived from dose volume histogram (DVH). All calculations were done for 6MV photon beams. By the 2D plans, the mean values of cold and hot areas were 26.4% and 8.1%, respectively. These values were reduced to 18.9% and 6.9% in 3D plans, respectively (p<0.000, p<0.01). Dose homogeneity was obtained 65.4% in the 2D and improved to 74.8% in the 3D plans (P<0.000). By the use of 3D plans, received dose within lung volume was decreased to 6.7% as compared with 8.9% of 2D plans (P<0.01). Application of 3D plans can lead to a more tumor control probability and cosmetic results, but less skin and lung side effects in patients with conserved breast.

In the light of various applications of UV laser in biological system, we have investigated the effect of picosecond UV laser radiation on silkworm Bombyx mori. The eggs of NB4D2 of different stages were exposed to pico second pulse laser at 355 nm from Nd:YAG laser for different durations. Due to irradiation alterations in crescent larval body markings, pupae with transpositioned antennae, pseudo abdominal and caudal legs were produced from 2 and 8 hr old embryos irradiated for 30 and 50 seconds respectively. Moths devoid of antennae and underdeveloped legs were also produced from 16 and 8 hr old embryos irradiated for 60 and 50 seconds respectively. The morphological anomalies were found highest in picosecond (6.16%) compare to nanosecond (1%) irradiated embryos at 8 and 16 hrs respectively and it is duration dependent. SDS-PAGE analysis of embryo revealed the occurrence of a 41 kDa new protein and delayed utilization of yolk proteins in the irradiated embryos. The larval haemolymph protein profile also exhibited 24, 25 and 6.2 kDa new protein bands. Embryo hatching, larval weight and cocooning rate was significantly affected and declined as duration of irradiation increases. It is clear from the present study that morphological anomalies and distinct variations in egg and haemolymph proteins establish a strong evidence that UV picosecond laser not only cause damage on embryonic cells but also interfere in transcriptional factors encode for organogenesis and proteins. Thus present study envisage the use of UV laser irradiation as a potential tool in investigating the embryonic and postembryonic development and cross-linking between DNA and protein using silkworm B. mori as molecular model.

In addition to gas pollutants, many chemicals and air pollutants are in the form of particulate matter. Particulate matter consists of a complex mixture of variable sized particles and physicochemical composition. These particles mainly contain minerals including Fe, Al, Ca, K, Cu, Ti, Mn, Ni, V and their size, chemical composition and concentration are important to assess the extent to which people has been protected. Instrumental neutron activation analysis (INAA) was employed to determine the composition of elements in material collected on whatman 41 filter using high volume air sampler in Rasht. Conce ntration of elements including Al, Ca, V, Mg, Cu, Ti, K, Ba, Cl, Mn, Na, As, Br, Cr, La, Sb, Co, Fe, Hg, Sc and Zn were determined in samples. Results showed that the levels of most air pollutants in Rasht to be lower than those measured in other cities in Iran (Tehran, Esfahan and Shiraz) by the same technique. Compared to other cities in world except for some elements, mean concentration of elements in air in Rasht were lower than those reported for Milan, Pavia and Beijing. Although the level of most air pollutants in Rasht are lower than those measured in other cities in Iran, due to considerable differences in element concentrations depending on the day of sample collection, more detailed studies are needed to control the emission of pollutants in this region.