جستجوی مقالات مرتبط با کلیدواژه "mcnpx code" در نشریات گروه "پزشکی"

Eye plaque brachytherapy is a suitable method for choroidal melanoma treatment. In eye tumors brachytherapy, 131Cs radioisotope has the potential to reach the highest dose to the cancerous tissue and the lowest dose to the healthy tissues. This study's aim is to investigate the received dose of choroidal melanoma tumor and right and left eye tissues in eye and water phantoms from a COMS plaque containing 131Cs seeds by simulation in MCNPX code.

First, two human eyes with full details, an 8-mm-high choroidal melanoma tumor in the right eye, and a 16-mm COMS eye plaque with 13 seeds of 131Cs that is perpendicular to the tumor were simulated in MCNPX code in an environment with dimensions of 30×30×30 cm3. Then, the absorbed dose resulting from one decay in the tumor and other tissues of the right and left eye were simulated in the eye and water phantoms, and based on that, the cumulative dose during the treatment in these tissues was calculated.

To deliver a cumulative dose of 85 Gy to the top of the tumor in 7 days, the activity of the 13 seeds of ¹³¹Cs for the eye and water phantoms should be equal to 21.86 and 23.32 mCi, respectively. In the water phantom, this activity results in the absorption of a 17.36 and 1.44 Gy cumulative dose more than in the eye phantom, in the tissues of the right and left eyes, respectively.

In this study, the cumulative dose of healthy tissues around the tumor in the eye phantom is lower than that in the water phantom, which is in agreement with the results of other studies. Therefore, by calculating the activity or treatment time using a phantom that is defined based on the actual dimensions of the patient's eye and the tumor inside it, it is possible to prevent more irradiation of the healthy tissues adjacent to the tumor, which also leads to the reduction of stochastic and nonstochastic effects.

Ionizing radiation modifies the molecular structure of the cell and ultimately disrupts its function. Brachytherapy by the Gamma Iridium-192 source is one of the most widely used radiotherapy methods in cervical and prostate cancer. For this reason, in the research, we investigated the damage to the DNA molecule by photons and secondary electrons of the source at different distances, and then we obtained the dose rates in the defined dimensions of DNA. In this work, using the MCNPX code, we calculated the flux and photon dose and secondary electrons from iradium-192 Brachytherapy, in approximate dimensions of DNA in a water phantom. Then, using the electron flux obtained, through the MCDS code, we investigated the efficiency of DNA breaks at different distances from the source. The simulations indicated that DNA damage is different at various distances from the source and it depends on the number of secondary electrons reaching that region as well as its energy. With increasing the distance from the source, the values of the probability distribution function of DNA single-strand and two-strand breaks diminish. It was also observed that these values had peaks at distances of 0.04 and 2.5 cm from the source, where the maximum probability of single-strand break at those distances was 8.06% and 3.9%, respectively, and the maximum probability of the two-strand break at those distances was 0.54% and 0.11%, respectively. It is notable that the dose reaching the DNA at these distances was 27.202 and 0.005 mGy/h, respectively.

Depth-dose distribution curve of protons in the matter has a maximum is called Bragg peak. Bragg peak of a monoenergetic proton beam is too narrow. The spread out Bragg peak should be created for full coverage of the tumor. The spread out Bragg peak is obtained in the depth of the tumor with superposition of the several Bragg peaks. The aim of this study was coverage of an eye tumor in the proton therapy while healthy eye tissue absorbs less radiation.
In this analytical study, the simulations were performed using MCNPX code. A tumor in the eye phantom was considered. The eye phantom has been irradiated with different proton beam energy. A Polystyrene modulator wheel was used for creating the spread out Bragg peak in the tumor region.
Bragg peaks were created in different depths of the tumor, by varying the proton beam energies from 20 MeV to 38 MeV. Bragg peak of the 32.85 MeV proton beam energy was precisely placed at the end of the tumor. Different pristine Bragg peaks were produced using a Polystyrene modulator wheel with different thicknesses and 32.85 MeV proton beam energy. The spread out Bragg peak was created in the tumor region by modulation of the pristine Bragg peaks. Neutrons and photons are produced by the inelastic nuclear interactions of protons with the nuclei of different tissues of eyes. The flux and absorbed dose of secondary neutrons and photons were considerably small compared to the depth-dose distribution of protons and the total absorbed dose in the tumor was more than other tissues of eyes.
Using a modulator wheel the tumor can be treated, so that the minimal damage reaches the surrounding tissues. The results show that more than 92% of the total dose of secondary particles and protons is absorbed in the tumor.

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.

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.