علی اصغر مولوی

Detecting the charge particles at Giga hertz rate is one of the applications of UFSD (Ultra-Fast Silicon Detectors). The UFSD test in front of the proton beam to count the beam particles and use it for a more precise Dose Delivery System for the treatment of the cancerous tumor by charge particles can become an effective step for the development of cancer treatment. In fact, this assessment is a prerequisite and guarantees the use of these detectors in the dose delivery system. In this regard, the best method for time measurement, which was CFD, was chosen. MATLAB software was used to measure and analyze the UFSD output signals. The results of the 50-μm-thick UFSD test and the various geometries that we performed in several different experiments at the CNAO Cancer Treatment Center in Italy, as well as the data obtained at the laboratory of CERN accelerator in Germany, were analyzed by the CFD method. The results of many different runs of programs in MATLAB for many registered signals show: 1- These sensors are reliable to count the proton particles in Giga hertz rate. 2-The CFD devices could be used to record the UFSD output signals. Therefore, they can be used in the correction of the dose delivery system as a counter for the proton number of the proton beam.

Some different time measurement methods have been presented for similar signals with the same trigger that one can choose by considering signal conditions. Finding the best time measurement method for the output signals from the UFSD (Ultra Fast Silicon Detectors) is our goal because we wanted to use these sensors to detect protons in the proton therapy system to treat cancerous tumors. Some different methods include Constant Fraction Discriminator (CFD), Cross-Correlation (CC), and Time over Threshold (TOT) by different data. These kinds of data include Data from Weightfield2 which is a UFSD signal simulator, Data from simulated signals in practice inside the laboratory, and experiment data, which are real data from the UFSD test in front of a Pico laser beam. Several programs in MATLAB software have been written and run to analyze and compare the different methods. The results are shown that CFD is the best method for time measurement finally

In the present study, we have systematically studied the role of surface energy coefficient as well as temperature dependence in the fusion hindrance phenomenon of the heavy-ion reactions using the proximity potential formalism. To this end, we have performed the calculations of the interaction potential using the original proximity potential 1977 (Prox. 77) and the fusion cross sections are calculated based on the coupled-channels (CC) approach. The considered fusion systems are including the heavy-ion reactions 11B+197Au, 12C+198Pt, 16O+208Pb, 28Si + 64Ni, 28Si + 94Mo, 58Ni+58Ni, 32S+89Y,34S+89Y, 12C+204Pb and 36S + 64Ni with conditions of Q <0 and charge product of the participant nuclei 392≤ Z1Z2 ≤784. Our preliminary calculations show the Prox. 77 model predicts the theoretical values ​​of the fusion cross-sections less than the corresponding experimental data especially in the energy regions below the fusion barrier. However, the imposing of the mentioned physical effects increases the calculated values of the fusion cross sections and thus improves their agreement with the experimental cross sections for the selected reactions. In addition, by considering the energy dependence on the surface energy constant γ0 of the proximity formalism at the low energy region we are able to reproduce well the fusion cross sections, the astrophysical factor S(E) as well as the logarithmic derivative L(E) in these regions.‎

Radon is a natural radioactive gas that easily enter to respiratory tract and cause considerable biologic damages. The main objective of this study was to determine the dose from the alpha and gamma radiations of radon decay chain products in trachea tissue using Monte Carlo simulation.

At first a trachea-equivalent cylindrical phantom was simulated by MCNPX Monte Carlo code. Then, dose profiles from alpha and gamma-emitter progenies were separately calculated. The daughter radionuclides were considered as suspended particles with uniform distribution inside the trachea inner volume.

The results showed that the received dose by trachea in alpha decay is considerably higher than that of gamma decay. The maximum administered dose by alpha decay was 1.72×10-16 Gy/decay. 218Po was had the highest dose among the studied alpha emitter daughter nuclides. The maximum administered dose by gamma decay was also equal to the 17.55×10-19 Gy/decay, where 214Pb and 214Bi had almost the same contribution in calculated dose.

The daughter radionuclides from radon decay chain, especially alpha emitter products of 218Po and 214Po, can be considered as a serious danger viewpoint to the internal exposure. These daughter nuclides can attach to the inner wall of trachea and remain in the respiratory system for long periods of time which can cause to the continuous exposure of trachea. Reducing the biologic effects of these internal radiation source requires especial schemes in order to avoid entering the radon and its radioactive daughters to human respiratory system, as much as possible.

Radiation therapy, is one of the treatments for cancer. Brachytherapy is a radiotherapeutic technique that a sealed radiation source is placed inside or next to the tissue and has become a mainstream treatment option for cancer. Achieving maximum dose to the gland as well as minimum injury to the adjacent tissues is a basic principle in radiation therapy. Sources configuration must be designed in such a way that the dose distribution agrees with treatment planning and the prescribed dose. Exact evaluation is necessary to avoid excessive dose to other organs especially organs at risk. Optimization algorithms are applied in preplanning treatment. The aim is to deliver a desire dose in the border of tumor while all of the points inside the tumor receive the absorbed dose more than the dose border values. The accuracy of optimization and finding the best position of seeds is so important in treatment planning. We used PSO algorithm to optimize the places of 103Pd seeds which are applied in the prostate brachytherapy. The algorithm was performed for desired tumor shape in various conditions. In circle and ellipsoid tumor with 5 and 40 desire seeds, more than 90% of points of border receive the prescribed dose. Moreover, the optimized characteristics of seeds and their best positions were determined. The results show that the PSO algorithm can be used for optimizing the position of interstitial implantation brachytherapy that so many seeds used. Distribution dose and isodose curve were studied to assurance delivering adequate dose to target volume while keeping healthy tissues. Few parameters, easy implementation and fast convergence around the global answer are advantages of this algorithm.

Determination of the relative biological effectiveness (RBE) of Auger electrons is a challenging task in radiobiology. In this study, we have estimated the RBE of internal conversion (IC) and Auger electrons released during Gadolinium neutron capture reaction (GNCR) by means of biological weighting functions (BWFs) with microdosimetric approach. Regarding the different distribution of Gadolinium (Gd) relative to the DNA as a target, the microdosimetric parameters of the Gd electrons were calculated using the Geant4 Monte Carlo toolkit and ROOT software. Assuming Gd infiltration into the cells and uniform distribution inside the Cell, the lineal energy distribution of Gd electrons in DNA was used instead of the lineal energy distribution of external radiations in the micrometer-diameter targets, which has been conventionally used in the mentioned methods.The results show that the calculated RBE values of Gd electrons using BWFs (2.68) for the case where Gd distributed at the center of the DNA are approximately equivalent to the RBE value of the therapeutic neutrons, which were measured in the literatures with the same biological conditions. According to the results, although the changes of the RBE of Gd electrons to the different distribution of Gd relative to the DNA are small, the amount of biological dose of the Gd electrons in the DNA is strongly dependent on the Gd distribution. In the case where Gd distributed at the center of DNA, the mean biological dose of Gd electrons in DNA during one GNCR (227.8 kGy.Eq) is large enough for occurring double-strand breaks (DSB) of the DNA. If we have accurate information about the spatial distribution of Gd or Auger-electron emitters inside the cell, by comparing to the results obtained in this study, we can have a better estimation of the RBE of the Gd electrons or in general Auger electrons.

Nowadays, due to the high costs and large dimensions of the conventional proton accelerators, other optimal methods for producing the proton beam have been studied. Using of Laser-driven proton accelerators is one of the important and new methods. In laser-driven ion acceleration, a highly ultra-intense laser pulse interacts with solid density targets and will create a plasma media that will accelerate ions and produce protons. Currently there are projects in this in field such as ELIMED, PMRC, DROT, HZDR and …. Due to the large angular dispersion of protons, reducing their dispersion and collimating them for transmission is very important. In this research, using the GEANT4 toolkit, the exact solenoid and its magnetics field for HZDR beamline have been simulated. The effect of solenoid on protons with a primary divergence of 5 degrees was investigated. The results show that consideration of the details of the solenoid has a direct effect on the calculation of the proton profiles and is necessary. The maximum of the solenoid magnetic field was calculated to ~20 Tesla to fit the proton selector system at a distance of one meter from the source.

In this work, for the first time, effect of gamma irradiation on the optical properties of CdS (quantum dots) QDs in various concentrations was studied. The aqueous CdS QDs were synthesized in a facile and fast method by using domestic microwave oven.  Three concentration of QDs; 20, 2, 0.4 mg/cc after different administrated dose of gamma irradiation (0-20 kGy) were studied. The results showed increased sensitivity of QDs after gamma irradiation with decreasing of concentration, so that the PL emission was completely vanished for concentration of 0.4 mg/cc after 20 kGy dose of irradiation. The optical results showed QDs were grown under gamma irradiation. Therefore, desired dose measurement can be carried out by choosing appropriate concentration for  gamma dosimetry.

This study aims to investigate changes in radon concentrations in residuals areas, using a sample closed room with the surface area of 12 m2. In the room, radon gas emitted from the floor and walls surfaces with different emission rates, and gaps under the door and around the window were the natural ventilation routes. Radon concentrations were measured in different points of the room in different circumstances and times using an accurate radon detector and then compared with the simulation results from Computational Fluid Dynamics (CFD) technique under corresponding conditions and times. The analytical data were used to validate the results of these two techniques. The results indicate that the radon concentration decreases from a relatively uniform distribution of about 81 Bq/m3 to a relative non-uniform distribution in the range from 12 Bq/m3 to 44 Bq/m3 after a very slow natural ventilation. The simulation results demonstrate an appropriate agreement with the experimental data that indicate the accuracy of performed modeling.

In this research, in order to improve our calculations in treatment planning for proton radiotherapy of ocular melanoma, we improved our human eye phantom planning system in GEANT4 toolkit. Different analytical models have investigated the creating of Spread Out Bragg Peak (SOBP) in the tumor area. Bortfeld’s model is one of the most important analytical methods. Using convolution method, a new analytical model for the creating of SOBP in the eye tumors was introduced. Also, the GEANT4 Monte Carlo toolkit was implemented for the Bragg peak production in the water and realistic eye phantom. Two different phantoms are proposed to study the effect of defining realistic materials on the proton dose distribution. Moreover, for the clinical investigation, the SOBP curves are figured in the water and eye phantom, using CATANA beam line. For proton pencil beams, the SOBP width for the water and eye phantoms was 0.901 and 0.877 cm, respectively. Bragg peak and SOBP calculations show a good agreement between the results of GEANT4, proposed and Bortfeld models. Using the CATANA beam line, the SOBP width difference between the two water and eye phantoms is 0.11 cm.

Sicne in many dosimetry calculations, the water and soft tissue phantoms are used, this study aimed to investigate the difference of these two phantoms with a phantom consisted of realistic liver materials in proton therapy for liver cancer.

Three phantoms with different materials of water, soft tissue and realistic liver materials were used for the study. A spherical tumor with 2 cm radius was considered in the liver. The Spread-out Bragg Peaks (SOBPs) were measured to cover the complete tumor for the three phantoms. Dose distribution and deposited dose ratio in tumor and surrounding organs were calculated using Monte Carlo N-Particle Extended (MCNPX) code. 

The best proton energy interval to complete the coverage of tumor in the liver for phantoms with realistic and soft tissue materials was 90-120 MeV and for water phantom, it was 88-116 MeV. The shift of the Bragg peaks depth per energy in the water phantom mm relative to two other phantoms was about 4.5. The dose parameters were evaluated according to the International Commission on Radiation Units and Measurements (ICRU), and the results showed no any significant difference between them. The dose distribution in the tumor and surrounding organs showed that for all three phantoms, the dose distribution around the tumor was negligible.

The use of soft tissue phantom has more acceptable results than water phantom in simulating treatment and can be replaced with realistic liver tissue. More realistic phantoms should be used in treatment plan. 

The use of soft tissue phantom has more acceptable results than water phantom in simulating treatment and can be replaced with realistic liver tissue. More realistic phantoms should be used in treatment plan.

Herein, the optical properties of CdS and Carbon quantum dots QDs for the first time under gamma irradiation was studied. The CdS QDs were synthesized by a rapid, facile and low cost microwave assisted method and carbon QDs extracted from orange juice by hydrothermal method. The samples were exposure by gamma ray with source of Co-60 within 0-20 kGy. The results showed that gamma irradiation suppress the photoluminescence PL intensity of QDs. A linear relation between PL intensity and logarithmic dose of gamma was found for the matrixed CdS QDs deposited top of glass. The initial size of CdS QDs was indicated about 3.4 nm by transmission electron microscopy TEM. For water-soluble CdS QDs and powdered carbon QDS, PL intensity was decreased as dose of 20 kGy gamma irradiation. These results shows that the luminescent nanostructure can be a new candidate for dosimetry.

Due to the increasing of closed ventilation systems used in buildings, the risk of indoor radon is increased day by day. In this study, we selected two sample rooms to calculate the radon emission coefficient from different levels, radon concentration measured when the natural ventilation was completely closed and compared with the analytical results. The results clearly show the difference in the amount of radon concentration at different levels; then, by overcoming the common gaps in the entrance of the rooms, the natural ventilation caused by the temperature difference between the room and the outside is obtained. By substituting them in the analytical equations, the radon concentration is calculated with ventilation. The calculated results are in good agreement with the experimental results and show the important role of natural ventilation to reduce indoor radon even to over 90%.

Treatment of radio-sensitized tumor is one of the promising modalities in radiotherapy. Since the different parameters and physical conditions vary in the treatments, the use of simulation models is easier, less costly and faster than practical methods for forecasting the solutions designed to optimize treatment. Therefore in this study, Monte Carlo simulations are applied to investigate the dose enhancement and the influential factors in photon therapy of silver nanoparticle radio-sensitized tumor. Consideration of the exact composition and sequence of the different tissues is the main task of this article. Head phantom with its actual composition was modeled by MCNPX code. Common tumor and silver nanoparticle radio-sensitized tumor are simulated. In this study, it was assumed that nanoparticles in the tumor are distributed homogeneously. Dose Calculation and its enhancement in photon therapy were calculated. The results show improved dose in the silver nanoparticles radio-sensitized tumor. This parameter is a linear function of concentration. Although silver k edge energy is 25.53 KeV, but optimized energy is between 35 to 45 KeV. Moreover, it is concluded that dose enhancement decreases by increasing the tumor depth.

Active faults are actually the most important factor in the entry of radon and thoron to the surface of Earth. The location of residential areas on these faults is one of the main reasons for increasing the concentration of these radioactive gases in them.
By using RTM1688, the concentration of Radon and Thoron was measured in 200 houses in rural residential areas placed on the active faults in Northern Khorasan in the north-east of Iran.
Radon measurements range was registered from 12Bqm-3 and 188 Bqm-3 with an average of 75.43 Bqm-3. The highest annual effective dose in samples was 5.45 mSv and the lowest was 0.35 mSv with an average of 2.187mSv. The range of Thoron was registered between 0.0 Bqm-3 and 840Bqm-3 with an average of 325.48 Bqm-3. The highest annual effective dose in samples was 21.17 mSv and the lowest was 0 mSv with an average of 8.20 mSv.
The results show that in close areas to active faults of north-east of Iran the concentration of Thoron and Radon is two to three times more than the safe level. It was found that 20 percent of residential areas are subject to annual effective dose greater than the limit for radon and 54 percent for Thoron. The high concentration of Thoron and Radon in these areas show that the active faults play the main role of producing of these gases which may increase of lung diseases.

Because of its radio-biological and physical advantages, proton therapy method is highly popular compared to other radiotherapy methods. Recent attempts at enhancing dose in tumors and reducing dose in adjacent tissues have been mainly relying on the use of metal nanoparticles with the aim of activating tumors. Numerous qualitative studies have been carried out on the safety and clinical use of gold nanoparticles and the results have been promising. However, some quantitative studies should be conducted to examine the factors affecting this method. With respect to the performance of Monte Carlo Method in simulation of the particles transport, the aim of this article was to obtain the dose enhancement in tumor sensitized by gold nanoparticles (GNPs) using MCNPX code.
A slab head phantom with homogenized-GNPs-aided tumor was considered to simulate proton therapy in brain tissue. Monte Carlo simulation was performed using MCNPX code to assess the dose and its enhancement in a radio-sensitized tumor by GNPs using proton therapy.
Findings: The Bragg peak calculations were conducted for proton beams with energies in the rage of 40-150 Mev. Dose and its enhancements in tumor were obtained for several concentrations. Then, Spread-out Bragg Peak (SOBP) was evaluated.
According to our calculations, if the protons energy is high enough so that they can pass the sensitized tumor; dose will be improved in Bragg peak and then, will decrease immediately. In addition, in relation to the SOBP, solid dose enhancement in sensitized tumor and decreasing the dose immediately after it, were concluded. Dose enhancement due to the presence of nanoparticles in the tumor confirms the results of previous research. But, a significant reduction in the dose immediately after the tumor was the result of this research.

Generally in radiotherapy via photon, healthy cells can be damage besides cancer cells; but in proton therapy these additional harms reach to its minimum. Because, proton deposit its maximum linear energy at the end of its trajectory known as Bragg pick. In this study, efficient range of energy in breast cancer treatment and estimation of secondary particle flux in proton therapy for indicating subsequent cancer risk is considered. In this study, at first we have simulated a semi-cylinder compressed breast phantom via MCNPX code and then we applied proton energy with 1MeV step in semi-cylinder phantom. Afterward, we have studied effects of this beam on tumor. The calculations show that the proper energy interval for tumor treatments with a thickness of 6mm with depth of 14 mm from the surface of the breast phantom is 41-48 MeV. In this study, secondary particle flux like neutron and photon with respect to proton initial energy has been calculated. Furthermore, flux diagram of these particle versus energy have been plotted. In neutron flux graph, the neutron spectrum has a significant intensity peak at low energy and flux intensity decreases smoothly as neutron energy increases. Also, in the photon flux spectrum, observed peaks are as a result of excitations in 31P, 12C, 16O nuclei. 12C nuclei produce maximum photon flux. Proton therapy is more precise than conventional radiotherapy and cause less damage to healthy non tumor cells. Because in the useful calculated range of energy, maximum dose or damage is exerted on tumor. However, this treatment method produces secondary particles that maybe damage other cells around the tumor.

Large quantities of radiopharmaceuticals prescribed for treatment and diagnosis are excreted through kidney. Therefore, radiation unwanted dose is created in kidney. As a result, exact calculation of prescribed medicine amount is important. In Mird pamphlet, 5 kidneys have considered in ellipsoidal shape that radiopharmaceutical is uniform distributed in them and gamma absorption fraction is calculated and recorded in the tables and the fraction of beta absorption is considered unit. While, kidney has internal organs and radioisotope is not uniform distributed in and beta absorbed fraction is not unit. In this research, for the first time kidney is considered integrated shape and for the second time has been considered that it is consisted of three areas, pelvis, medulla and cortex. It is supposed that radiopharmaceutical is distributed in medulla. Then, beta absorbed dose is calculated in medulla and cortex using MCNPX code and is compared with integrated kidney results. Resuts: This research has been showed that beta absorbed dose from 203Hg, 166Ho and 177Lu isotopes in medulla is four times as much as dose in integrated kidney and beta dose in cortex is 0.004 to 0.012 times as much as beta dose in integrated kidney. Internal structure of kidney should be considered in simulation to achieve a more accurate prescribed dose. It is recommended that simulation results of three areas kidney are replaced with integrated kidney to prevent from renal toxicity.

Radon and Thoron are the radioisotopes which radiate high alpha energy particles. These two gases can enter in the body by different ways such as inhalation, eating and drinking and then destroy body`s internal tissues and cause the lung cancer. The condensation of these gases differs in various areas and is more in zones near active faults. In this research, first the relation of Radon and Thoron concentration with the effect of distance of North east active faults in about 100 residential places of Iran is studied. Results show that residential places near active faults have more concentration of Radon and Thoron than other places. Also in these places the concentration of Thoron is two or three times more than Radon. The maximum amounts of Radon and Thoron concentration are 188Bq/m3 and 803Bq/m3 with the average amounts of 71.52Bq/m3 and 326/44Bq/m3 respectively.

One of the common methods of breast cancer diagnosis is x-ray mammography. Because of the sensitivity of the breast tissue¡ patient absorbed dose in the mammography is very important. The purpose of this study is investigation of the influencing factors on the amount of absorbed dose and comparison of the absorbed dose by use of the target-filters Mo-Mo and W-Rh in the mammography device. In this study¡ the simulation of the x-ray tube of the mammography device were done by use of the MCNPX code¡ and spectrum of the common filter of Mo-Mo and newer compound of W-Rh were calculated. Then¡ for calculation of the absorbed dose¡ the breast phantom condition were simulated. We compare absorbed dose of the two common target-filter combinations which used in the mammography system. In addition to¡ we study the effect of the different factors; such as voltage¡ thickness of skin and glandular tissue of the breast on the absorbed dose level. Patient absorbed dose by use of the target-filter combination of W-Rh is less than the Mo-Mo combination¡ so this combination can be a good alternative for Mo-Mo target-filter. The present study shows that the voltage¡ thickness of skin and glandular tissue of the breast has a significant effect on the patient absorbed dose.

Optimization in radiotherapy is one of an important and attractive topic in Medical Physics. In this study, we have written a computer code base on genetic algorithm using MATLAB software, to optimize the best places of brachytherapy sources with optimal value of a parameter which is determined by weight. The weight parameter is related to the activity of each seed implant brachytherapy sources, such as iodine -125, or the irradiation time in each place after loading brachytherapy source like Iridium-192. We have run the code for some arbitrary tumor’s shapes in two and three dimensions spaces and the optimized places for seeds of Ioine-125 brachytherapy source and their activities are founded. For each tumor, the optimization is done so that the points on the boundary edge of two-dimensional or three-dimensional object, points on the surface and all points within a given dose greater or equal to the dose on the surface or in the border areas have. The Isodose curves show the result of dose optimization is done at the desirable level.

The 131I radioisotope is used for diagnosis and treatment of hyperthyroidism and thyroid cancer. In optimized Iodine therapy, a specific dose must be reached to the thyroid gland with minimum radiation to the cervical spine, cervical vertebrae, neck tissue, subcutaneous fat and skin. Dose measurement inside the alive organ is difficult; therefore the aim of this research was dose calculation in the organs by MCNPX code. First of all, the input file for MCNPX code has been prepared to calculate F6 and F8 tallies for ellipsoidal thyroid lobes with long axes is tow times of short axes which the 131I is distributed uniformly inside the lobes. Then the code has been run for F6 and F8 tallies for variation of lobe volume from 1 to 25 milliliters. From the output file of tally F6, the gamma absorbed dose in ellipsoidal thyroid, spinal neck, neck bone, neck tissue, subcutaneous fat layer and skin for the volume lobe variation from 1 ml to 25 ml have been derived and the graphs are drew. As well as, form the output of F8 tally the absorbed energy of beta in thyroid and soft tissue of neck is obtained and listed in the table and then absorbed dose of bate has been calculated. The results of this research show that for constant activity in thyroid, the absorbed dose of gamma decreases about 88.3% in thyroid, 6.9% at soft tissue, 19.3% in adipose layer and 17.4% in skin, but it increases 32.1% in spinal of neck and 32.3% in neck bone when the lobe volume varied from 1 to 25 milliliters. For the same situation, the beta absorbed dose decreases 95.9% in thyroid and 64.2% in soft tissue. For the constant activity in thyroid by increasing the thyroid volume, absorbed dose of gamma in thyroid and soft tissue of neck, adipose layer under the skin and skin of neck decreased, but it increased at spinal of neck and neck bone. Also, by increasing of the lobe volume in constant activity, the beta absorbed dose reduced. Therefore, whatever the thyroid lobe is small the administered value of 131I increased to induce the suitable dose.

In this paper, an algorithm base on Monte Carlo simulation for pileup effect in gamma spectrum of a detection system is presented whose its code was written in FORTRAN language. The code can be run in paralayzable and nonparalazable mode to obtain the pileup distortion and value of pulses pileup for any detection system. The result show, that the computed spectrum of 137Cs is in good agreement with the experimental spectrum in NaI(Tl) detector. The free of pileup free spectrum and sub-spectra with different degrees of pulses of pileup are calculated. Also, we can apply it to different sources and detectors for pileup correction.

Average glandular dose calculation in mammography with Mo-Rh target-filter and dose calculation for different situations is accurate and fast. In this research, first of all, x-ray spectra of a Mo target bombarded by a 28 keV electron beam with and without a Rh filter were calculated using the MCNP code. Then, we used the Sobol-Wu parameters to write a FORTRAN code to calculate average glandular dose. Average glandular dose variation was calculated against the voltage of the mammographic x-ray tube for d = 5 cm, HVL= 0.35 mm Al, and different value of g. Also, the results related to average glandular absorbed dose variation per unit roentgen radiation against the glandular fraction of breast tissue for kV = 28 and HVL = 0.400 mmAl and different values of d are presented. Finally, average glandular dose against d for g = 60% and three values of kV (23, 27, 35 kV) with corresponding HVLs have been calculated. Discussion and The absorbed dose computational program is accurate, complete, fast and user friendly. This program can be used for optimization of exposure dose in mammography. Also, the results of this research are in good agreement with the computational results of others.

Clinical application of encapsulated radioactive brachytherapy sources has a major role in cancer treatment. In the present research, the effects of different tissue densities on the dose distribution of a 103Pd brachytherapy source in a spherical phantom of 50 cm radius have been studied. As is well known, absorbed dose in tissue depends to its density, but this difference is not clear in measurements. Therefore, we applied the MCNP code to evaluate the effect of density on the dose distribution. 103Pd brachytherapy sources are used to treat prostate, breast and other cancers. Absorbed dose has been calculated and presented around a source placed in the center of the phantom for different tissue densities. Also, we derived anisotropy and radial dose functions and compared our Monte Carlo results with experimental results of Rivard and Li et al. for F(1, θ) and g(r) in 1.040 g/cm3 tissue. The results of this study show that relative dose variations around the source center are very considerable at different densities, because of the presence of a photoabsorber (Au-Cu alloy) in the source core. Dose variation exceeds 80% at the point (Z = 2.4 mm, Y = 0 mm). Computed values of anisotropy and radial dose functions are in good agreement with the experimental results of Rivard and Li et al.