ABSTRACT
The advantages of proton beam in radiation therapy- like small lateral scattering as well as absence of exit dose tail in the organs which are after the tumor- make it capable of delivering more treatment doses to the target and much lesser to the critical tissues near it. In this study, the Monte Carlo MCNPX code has been used to simulate a slab head phantom irradiated by proton pencil beams. The simplified slab has tissue compositions of the ICRU 46, and the necessary data have been taken from adult male phantom of MIRD-ORNL family series. Suitable energy range of incident proton beams has been estimated in order to have the Bragg peaks inside the brain tissue. Energy straggling or, rather, range straggling, and multiple scattering which affect the lateral broadening of incident beams, have been investigated. The results show that the FWHM [Full Wide in Half Maximum] increases more than six times from 1.73 mm to 10.78 mm for the energy range of 50 - 135 MeV. The FWHM values of lateral dose profiles change from 1 mm in 50 MeV to 7.5 mm in 135 MeV, and it has been shown that when a pencil beam is used to irradiate a tissue, the absorbed dose in depth along the central axis does not show a Bragg peak pattern
Subject(s)
Brain , Phantoms, Imaging , Scattering, RadiationABSTRACT
Radon concentration was measured in 50 drinking water samples in Mashhad - Iran. The tap water used for drinking and other household usages can increase the indoor radon level. Drinking water samples were collected from various places and supplies of public water used in Mashhad. Then radon concentration has been measured by portable radon gas surveyor SILENA [PRASSI] system. The results showed that about 70% of water samples had radon concentration greater than 11Bq/l the level recommended USA environmental protection agency [EPA]. The arithmetic mean of radon concentration for all samples was 16.238 +/- 9.322 Bq/l. Also the annual effective dose in stomach and lung per person were estimated in this research, with the mean value of 0.040 mSv and 0.043 mSv per year for these two organs for all samples, respectively. The results indicate that radon concentrations in public drinking water samples of Mashhad are mostly low enough and below the proposed concentration limits. The mean radon level was 16.238 Bq/l for all samples; which is not much greater than 11Bq/l as EPA advised level. Further, only two samples induced the total annual effective dose greater than 0.1 mSv per year
ABSTRACT
Skin cancer can be treated by various methods. Electron radiotherapy has been a useful therapeutic modality in the treatment of skin cancers in areas which are difficult to cure by other methods. Depth dose distribution of [166]Ho using VARSKIN2 code is presented in this work. Depth dose distribution of [166]Ho was calculated, using VARSKIN2 code by adding of [166]Ho data to the library of VARSKIN2 code. After adding [166]Ho radionuclide data to the library of the code, it was run for various input parameters including: density, air gap thickness, radiation time and different source geometry. Different forms of sources which have been used in this research are 2-D disk, cylindrical and spherical shapes. The result showed that the skin absorbed depth dose variation was an exponential function because of short range of beta ray. Dose gradient was very high near the sources. For the same activity, disk source induced a dose more than spherical and cylindrical source to skin surface. Superficial skin tumors could be successfully treated by topical application of beta-emitting [166]Ho source. VARSKIN2 is a fast, accurate and user friendly code for beta dosimetry and can be used for dose optimization calculation, especially in beta source over the human skin
Subject(s)
Humans , Holmium , Radiometry , Treatment OutcomeABSTRACT
Accurate computation of the radiation dose to the breast is essential to mammography. Various the thicknesses of breast, the composition of the breast tissue and other variables affect the optimal breast dose. Furthermore, the glandular fraction, which refers to the composition of the breasts, as partitioned between radiation-sensitive glandular tissue and the adipose tissue, also has an effect on this calculation. Fatty or fibrous breasts would have a lower value for the glandular fraction than dense breasts. Breast tissue composed of half glandular and half adipose tissue would have a glandular fraction in between that of fatty and dense breasts. Therefore, the use of a computational code for average glandular dose calculation in mammography is a more effective means of estimating the dose of radiation, and is accurate and fast. In the present work, the Sobol-Wu beam quality parameters are used to write a FORTRAN code for glandular dose calculation in molybdenum anode-molybdenum filter [Mo-Mo], molybdenum anode-rhodium filter [Mo-Rh] and rhodium anode-rhodium filter [Rh-Rh] target-filter combinations in mammograms. The input parameters of code are: tube voltage in kV, half-value layer [HVL] of the incident x-ray spectrum in mm, breast thickness in cm [d], and glandular tissue fraction [g]. The average glandular dose [AGD] variation against the voltage of the mammogram X-ray tube for d = 4 cm, HVL = 0.34 mm Al and g=0.5 for the three filter-target combinations, as well as its variation against the glandular fraction of breast tissue for kV=25, HVL=0.34, and d=4 cm has been calculated. The results related to the average glandular absorbed dose variation against HVL for kV = 28, d=4 cm and g= 0.6 are also presented. The results of this code are in good agreement with those previously reported in the literature. The code developed in this study calculates the glandular dose quickly, and it is complete and accurate. Furthermore, it is user friendly and useful for dose optimizing in mammography imaging
Subject(s)
Female , Humans , Breast/anatomy & histology , Breast/radiation effectsABSTRACT
Monte Carlo determination of TG-43 brachytherapy dosimetry parameters and dose distribution calculation for [131]Cs source model CS-1 are presented in this study. The dose distribution was calculated around the [131]Cs Model CS-1 located in the center of 30 cm x 30 cm x 30 cm water, and soft tissue phantoms cube using MCNP code by Monte Carlo method. The percentage depth dose [PDD] variation along the different axis, parallel and perpendicular, the source was calculated. Then, the isodose curves for 100%, 75%, 50% and 25% PDD were constructed. Finally, F[r, theta] and g[r] dosimetry parameters of TG-43 protocol have been determined. Results obtained show that the Monte Carlo method could only calculate dose deposition in high gradient region, near the source, accurately. The energy cut off was found to be 1 eV and the error in the calculations was less than 2%. The isodose curves of the CS-1 [131]Cs source were constructed from dose calculation by MCNP code. The calculated dosimetry parameters for the source were in agreement with previously published results
Subject(s)
Cesium Radioisotopes/analysis , Radiometry/methods , Radiation DosageABSTRACT
Palladium-103 [[103]Pd] is a brachytherapy source for cancer treatment. The Monte Carlo codes are usually applied for dose distribution and effect of shieldings. Monte Carlo calculation of dose distribution in water phantom due to a MED3633 [103]Pd source is presented in this work. The dose distribution around the [103]Pd Model MED3633 located in the center of 30×30×30 cm[3] water phantom cube was calculated using MCNP code by the Monte Carlo method. The percentage depth dose [PDD] variation along the different axis parallel and perpendicular to the source was also calculated. Then, the isodose curves for 100%, 75%, 50% and 25% PDD and dosimetry parameters of TG- 43 protocol were determined. The results show that the Monte Carlo Method could calculate dose deposition in high gradient region, near the source, accurately. The isodose curves and dosimetric characteristics obtained for MED3633 [103]Pd source are in good agreement with published results. The isodose curves of the MED3633 [103]Pd source have been derived form dose calculation by MCNP code. The calculated dosimetry parameters for the source agree quite well with their Monte Carlo calculated and experimental measurement values
ABSTRACT
[131] radionuclide has been widely used for treatment of thyroid cancer and hyperactivity. In this regard the accurate calculation of absorbed dose in thyroid gland and other organs is important. In this study, according to MIRD method, MCNP code was used for calculation of absorbed dose of [131] radioactive sources in any thyroid with specific mass and size. The results of two different geometries spherical and cylindrical shapes for each lobe of thyroid were compared. The results show when the thyroid mass increase from 20gr to 70gr, the absorbed dose per one disintegration increases 4.2%. These results firstly indicate that instead of using the total mass of thyroid in iodine therapy, it would be better to use the calculated active mass of thyroid. Secondly, the variation of absorbed dose per disintegration of [131] should be considered for the measurement of source activity in treatment of thyroid hyperactivity or cancer
Subject(s)
Radiation Dosage , Radioactivity , Iodine Radioisotopes , RadiopharmaceuticalsABSTRACT
Natural uranium exists in earth crust and seawater. The concentration of uranium might increase by human manipulation or geological changes. The aim of this study was to verify susceptibility of laser flourimetry method to determine the uranium concentration in Caspian Sea and Persian Gulf water. Laser flourimetric method was used to determine the uranium concentration in several samples prepared from Caspian Sea and Persian Gulf water. Biological and chemical substances were eliminated in samples for better evaluation of the method. As the concentration of natural uranium in samples increases, the response of instrument [uranium analyzer] increases accordingly. The standard deviation also increased slightly and gradually. Results indicate that the laser flourimetry method show a reliable and accurate response with uranium concentration up to 100 micro g/L in samples after removal of biological and organic substances