International Journal of Radiation Research
Volume:8 Issue: 2, Apr 2010

This work investigated the dosimetry limitations of the random and systematic uncertainties of sliding window (SW) intensity modulated radiation therapy (IMRT). A Varian 21EX linear accelerator, Pinnacle3 treatment planning system and radiographic film dosimetry was used. The limitations of the SW were studied using beam modulation ranging from 2 to 100 MU/beam, DR from 100 to 600 MU min-1, LV from 1 to 5 cm s-1 and field size up to 12 × 12 cm2. The random and systematic errors were investigated using clinical and flat beams, as well as beams of high profile modulation including linear, exponential, and sinusoidal profiles. The leading edge and plateau of the SW profiles have a significant deformation for higher DR and for beams of < 10 MUs/beam. It was found that the error is directly proportional to the DR and LV, and inversely proportional to the number of MU/beam. The high DR and LV are limiting factors, producing random profile deformation when SW beams of small number of MU/beam are delivered. A very good agreement was found between the planned and delivered geometrical and clinical dose profiles when beams > 10 MUs irradiated by a DR from 100 to 600 MU min-1 and LV from 1 to 5 cm s-1. After the proposed correction, an average difference < 0.5% for clinical profiles was measured for beams irradiated with DR = 600 MU min-1 and LV= 5 cm s-1. It was concluded that this correction methodology may serve as a pre-treatment Quality Assurance tool for SW IMRT beams.

The radioprotective effect of Grewia asiatica fruit (GAE) which contains anthocyanin type cyanidin 3- glucoside, vitamin C, A, minerals, carotenes and dietary fibers etc was studied. For study Swiss albino mice were divided into five groups-1. Control (vehicle treated) 2. GAE treated (700 mg / Kg. b.wt / day for fifteen days), 3. Irradiated (5 Gy), 4. GAE + Irradiated and 5. Irradiated + GAE treated. The irradiation of animals resulted in a significant depletion in the DNA and RNA level at all intervals studied viz 1-30 days in comparison to control group. Treatment of mice with GAE before and after irradiation caused a significant elevation in liver DNA and RNA level in comparison to irradiated mice. Photomicrograph of liver histology also showed that pre and post supplementation of GAE provides protection against radiation. Similarly counting of different type hepatocytes also showed that GAE protect the liver against radiation. Thus biochemical and histopathological results proves that GAE has the potential against radiation.

Accurate voxel phantom is needed for dosimetric simulation in radiation therapy for malignant tumors in female pelvic region. However, most of the existing voxel phantoms are constructed on the basis of Caucasian or non-Chinese population. A computational framework for constructing female pelvic voxel phantom for radiation dosimetry was performed based on Chinese Visible Human (CVH) datasets. First, several organs within pelvic region were segmented from CVH datasets. Then, polygonization and voxelization were performed based on the segmented organs and a 3D computational phantom is built in the form of a set of voxel arrays. The generated phantom can be converted and loaded into treatment planning system for radiation dosimetry calculation. From the observed dosimetric results of those organs and structures, we can evaluate their absorbed dose and implement some simulation studies. A voxel female pelvic phantom was developed from CVH datasets. It can be utilized for dosimetry evaluation and planning simulation, which would be very helpful to improve the clinical performance and reduce the radiation toxicity on organ at risk (OAR).

In Radiation Therapy, the sparing of normal tissues can be performed using either multi-leaf collimators or Cerrobend blocks. The current work focuses on the physical characteristics of Cerrobend blocks including attenuation coefficient, effective penumbra width and isodose curves undulation in penumbral regions. All measurements were performed using a dual energy linac and the Cerrobend blocks designed and fabricated using a commercial Cerrobend material. Data were collected using a calibrated ionization chamber as well as EDR2 films. The results showed that the attenuation coefficient was found to be 0.4475 and 0.4276 cm-1 for photon beams 6MV and 15 MV, respectively, and a potential air bubble with a diameter greater than 3 mm affects beam attenuation significantly. The optimum Cerrobend block width was found to be around 16 mm. The isodose curves scalloping achieved for secondary collimator jaws, were also similar. If Cerrobend blocks are used as a basic method to protect normal tissues, its physical characteristics will be recommended to be taken into account comprehensively.

The sources of radioactivity in the environment have natural, terrestrial and extraterrestrial, and anthropogenic origins. Plants may get radioactive nuclides in two ways: (i) by the deposition of radioactive fallout, (ii) by absorption from the soil. The Concentrations of the natural radionuclides (226Ra, 228Ra, 40K) and the artificial radionuclide (137Cs) in leek and parsley in Tehran province-Iran were determined using HPGe. Also the effective dose due to the ingestion of such vegetables by the population of Tehran province was studied. The average value of radionuclide concentrations in parsley samples were measured 177.69 ± 12.47 mBq kg-1 fresh for 226Ra; 349.62 ± 28.42 mBq kg-1 fresh for 228Ra; 187364.6 mBq kg-1 fresh for 40K. The average value of radionuclide concentrations in leek samples were measured 94.31 ± 6.46 mBq kg-1 fresh for 226Ra; 207.47 ± 19.46 mBq kg-1 fresh for 228Ra; 174555 ± 1704.21 mBq kg-1 fresh for 40K. The concentrations of 137Cs in most of Parsley and Leek samples were below the minimum detectable activity (MDA). The Average 226Ra and 228Ra activities in 29 leek and parsley samples were about 2.63 and 6.78 times the reference values, respectively. The annual effective dose resulting from the studied radionuclides for the adult population in Tehran province were found to be safe in comparison with normal background areas.

Photon attenuation as an inevitable physical phenomenon influences on the diagnostic information of SPECT images and results to errors in accuracy of quantitative measurements. This can be corrected via different physical or mathematical approaches. As the correction equation in mathematical approaches is nonlinear, in this study a new method of linearization called ‘Piece Wise Linearization’ (PWL) is introduced and to substantiate its validity for SPECT image reconstructions, a phantom study is performed. A SPECT scan of a homemade heart phantom filled with 2 mCi 99mTc was acquired by dual head Siemens E.Cam gamma camera equipped with LEHR collimator. Row data of the scan were transferred in DICOM format to a pc computer for reconstruction of the images using MLEM iterative algorithm in Matlab software. Attenuation map of the phantom µ(x) were derived using PWL with linear optimization approach. Based on that, the attenuation corrected SPECT image of the phantom were reconstructed and compared with non-corrected image, using MLEM iterative algorithm. Comparison of the corrected and non-corrected images confirmed with CT attenuation correction method. Attenuation correction in SPECT image can be achieved successfully, using emission data and piecewise linearization with linear optimization approach. The corrected image of f(x) and attenuation map µ(x) of the heart phantom using this approach promise acceptable image quality for diagnostic clinical use.

Proton induced X-ray emission (PIXE) has been applied as reliable and improved techniques in this study to compare concentration of various trace elements in normal and abnormal varicose veins. Five samples from normal veins and 13 samples from varicose veins bombarded by 2.0 MeV energy proton beams produced by a Van de Graff accelerator in vacuum. Two specimens from each sample, approximately 1cm, were processed for PIXE (proton induced X-ray emission) analysis. Both qualitative and quantitative analyses of potassium, iron, copper and zinc concentration were performed with respect to calcium concentration. The concentration of potassium and iron in the varicose vein group has been significantly higher than the normal group. Copper and zinc concentration were also higher in the varicose veins, and the elevation of bromine was seen in the normal group. PIXE analysis showed higher concentrations of trace elements in veins derived from varicos patients compared to normal group. The difference in normal and abnormal vein might be independent of age.

The Singh index is an inexpensive simple method to evaluate bone density, commonly used to assess osteoporosis is based on the radiological appearance of the trabecular bone structure of the proximal femur on a plain antero-posterior (AP) radiograph. The purpose of this study was to compare between Singh index and bone mineral density measurement using dual energy X-ray absorptiometry (DXA). Three orthopedists evaluated radiographs of 72 patients suspected with osteoporosis. The inter-observer agreements of the Singh index were obtained by using kappa statistics. The bone mineral density (BMD) of proximal femur was measured by DXA in all patients, and then the BMD results were compared with those of Singh index by using reference radiographic charts of the Singh index method. Dual-energy X-ray absorptiometry was used to measure bone mineral density. A Norland XR46 system was used for the investigations. The inter-observer agreement kappa values were 0.01, 0.07 and 0.09 (mean value: 0.05) and the strength of the observer agreements was negligible. The obtained osteoporosis prevalence among the studied patients was 38.9%. The inter-observer variation was large, there was no any correlation between the Singh index and bone densitometry. So, the index cannot be used; for evaluating and osteoporosis diagnosis, because of its low reliability.