جستجوی مقالات مرتبط با کلیدواژه « رادیوتراپی » در نشریات گروه « فیزیک »

High energy photons (10-20 MeV) that originate form medical linear accelerator in Radiotherapy treatment room, produce neutron. The produced neutrons id absorbed with different materials in the accelerator, the environment and even patient body that produced radioactive materials. These radioactive materials may pose a risk of radiation exposure to the radiotherapists who go to the treatment room frequently between patients. This process may cause internal radiation exposure in addition to external radiation exposure.  In this research after the expose of 18 MV X-Ray by medical accelerator (Varian 2300C/D), the spectrum of accelerator head was collected by portable HPGe detector and 19 radioisotopes were recognized.

Lung cancer is one of the most common types of cancer with a high mortality rate among men and women.  This type of cancer, by involving the arteries and lymph nodes, causes the cancerous mass to spread regionally and metastasize. Radiation therapy using teletherapy method and the use of Siemens linear accelerators is one of the most effective non-invasive treatments for lung tumors. In the present study, using Monte Carlo statistical technique and MCNPX2.6 transport code, simulation calculations of treatment process with female ORNL phantom modeling including tumor tissue in the right lung wall and LINAC linear accelerator and validation at 6 and 18MV energies were performed. According to the results, it can be concluded that to control secondary abnormalities during or after the treatment process in the target tissue and other vital organs, increasing the depth and voltage and reducing the treatment time will reduce the dose received by clinical tissues from the electron beam source.

Radiotherapy using various beams is one of the methods for treating cancer, Hadrons  used   to  treat cancers  that  are  near critical organs. The most important part of the cell that is damage by ionizing radiation is DNA. In this study, damages induced in the  genetic material of  living cells (DNA) defined by  the  atomic model from the  protein data bank (PDB) have been studied by  radiation of monoenergetic protons and its secondary particles using  Geant4 code. The total SSB yield is independent of energy of incident particle. The total DSB yield is increase with increasing of  incident particle LET. The ratio of total inelastic events to absorbed dose for primary protons as well as its  secondary particles is independent of energy. The contribution of  secondary particles in the formation  of  single-strand  breaks and double-strand breaks have been calculated. The DSB yield generated by secondary particles is increase with decreasing the energy of the incident particle and the contribution of  secondary particles to the generate of double-strand break for energies less than 5 Mev  is greater than their contribution to the creation of single-strande breaks. The ratio of double-strand breaks to single- strand breaks have been reduced by increasing  the energy of   the radiation particle.

Charged particles such as protons and carbon ions are an increasing tool in radiation therapy. However, unresolved physical problems prevent optimal performance, including estimating the deposited dose in non-homogeneous tissue, is an essential aspect of optimizing treatment. The Monte Carlo (MC) method can be used to estimate the amount of radiation, but, this powerful computing operation is very expensive, and has the ability to restrict it. In this work, we use basic physics in the form of the Bethe equation to provide a new analytical solution for range, energy and LET of particles. This solution is presented in terms of the functional integral by converting the relativistic harmonics, which allows it to be used at the level of radiotherapy energy (protons 50-350 MeV, carbon ions of 100-600 Mev / a.m.u). The agreement along the path of the particles, with some differences in reaching the path is high. The model presented in an optimization framework for radiation particle radiation is estimated as a rapid method for dose and LET, which is able to account for heterogeneity in electron density and ionization potential.

The aim of this study was to estimate the delivered doses to tissues and organs around the liver tumor during radiotherapy and to determine organs with a high probability of secondary induction cancers. This study was carried out using Monte Carlo method.
The used Phantom, the ORNL phantom is for an adult female. The volume of the tumor is as much as 30% of the liver tissue.In the initial step of this study, we will focus on simulating the linear accelerator of Varian 2100 6MV and by comparing the output results with the calculated values;​​ we will make sure that the results of MCNPX code are sufficiently accurate. In the next step, the corrections are considered in phantom and Monte Carlo technique was used for radiotherapy. The dose calculations was done for 38 organs. According to the obtained results in this simulation, the reached doses to other tissues surrounding tumor was in the range of 0.01-13.07%. Among the examined organs, the healthy tissue of the liver, kidney, the left part of bone_rib cage, the right part of bone_rib cage, adrenals pancreas and lung have received 88, 24.5, 24.2, 18.8, 15.9, 7, 5 cGy, respectively. Due to the linear relationship between the dose received in each organ and the risk of cancer of the organ in subsequent years, in the BERT model, the kidneys have a higher risk of secondary cancers than other organs. In calculating of the risk by Monte Carlo method at a given time, the healthy part of the liver has the highest risk of inducing secondary cancers, and the risk of inducing secondary cancers for kidney, the right part of cage, the left part of cage and adrenal glands were 81, 48, 36 and 18 percent, respectively. Secondary cancer induction is more likely for patients who require more therapy for effective radiotherapy than other patients.

Recent studies suggest that relative biological damage (RBD) may change from in to out off field regions for 6 MV photon beams. In this study RBD was calculated in and out of field of 30x30 cm2 and 40x40 cm2 6 MV clinical photon beams including low energy slowing down electrons in track length estimated method. Varian 2100C/D linear accelerator was simulated using MCNPX code. Electron and photon spectra at energies higher than 2 keV were collected in a water phantom at different depths and off-axis points. New extrapolation method was used to estimate the electron spectra at energies lower than 2 keV. These spectra were used as an input to MCDS code to calculate the RBD of induced damage in DNA. There was an observable difference in the energy spectra for photons and electrons for points in the primary radiation field and those points out-of-field. RBD increases up to 10% for 10 MV photons in the out-of-field region. This work supports the hypothesis that in megavoltage treatments at the out-of-field, radiation quality can very enough to have an impact on RBD per unit dose.