جستجوی مقالات مرتبط با کلیدواژه "medical linear accelerator" 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.

Medical electronlinear accelerators are the most practical radiotherapy facilities in cancer treatment. About 52 percent of patients are treated by these radiotherapy systems during their treatment process. However, in developing countries there are not enough systems and recent studies reported the shortage of 5000 megavoltage radiotherapy accelerators all over the world. According to international standards, there is a need of one medical linac for 180000 patients. In Iran, cancer is the third cause of death after cardiovascular diseases and accidents. This study indicates the number and status of medical electron accelerators in radiotherapy centers in Iran.

During the radiation therapy with electron beam, due to electron interaction and scattering from structures of the head of the medical linear accelerator, unwanted photons are produced. The main contribution of the photon contamination is resulted from the various components of the medical linear accelerator on the way of the high energy electron beam, and few percent is due to the interaction of the beam with the phantom or the patient's body. Structure and material of the head of the medical linear accelerator have effective roles on production of x-rays dose from the electrons beam. Therefore, the parameters of electron beam produced by a linear accelerator manufactured by different companies were varied. This difference may be seen even among the accelerators produced by one company. Therefore, this parameter must be described separately for each machine. In order to measure photon contamination at the electron mode of the Elekta Precise linear accelerator, thermoluminescence detectors (TLD700 & GR200) at two energies (10 & 15MeV) in polyethylene phantom were applied. These data were compared with the calculations using MCNPX code. Our results show an appropriate match between theory and experimental data at both energies. It shows that the rate of produced bremsstrahlung photons dose for tallies that are close to the phantom are in mSv range. Then it will be possible to calculate bremsstrahlung photon dose for different point of radiotherapy room of the Ayat-O-lah Khansari hospital by the Monte Carlo codes.

Electron beams are widely used in radiation therapy. Since the nominal electron energy value is not quite meaningful for physics or dosimetry purposes in treatment planning, depth dose data for electron beams must be determined and used. The purpose of this study was to obtain the depth dose data for the 6 and 8 MeV electron beams of a NEPTUN 10PC linac and evaluating its beam characteristics using Monte Carlo method. The linac electron beams were modeled using the BEAMnrc code. The DOSXYZnrc code was also used for the simulation of RFA 300 water phantom. The central axis depth dose and the beam profiles were calculated for the beam energies at the 10×10 cm2 field size. The R100, Rq, R85, R50 and Rp parameters were extracted from the normalized depth-dose curves. The calculated results were compared with the experimental data, where the agreement between them was very good. Since different linacs from the same manufacturer and model usually have the same structures, it seems that it can be possible to model different linacs based on a particular one from the same manufacturer by defining their energy spectra and the beam quality indexes. In addition, using this method enables us to assess the characteristics of the electron beam at the exit of the linac and the effects of every part of the linacs head structure on the electron beams. It may also be possible to study and evaluate the final dose distribution.