Abstract:The total attenuation coefficients of 11 biological targets against photon energies were plotted within the energy range 1-10 MeV. From these plots a possible equation describing the relationship between photon energy and the total attenuation coefficient was derived. The suggested equation is µ / ρ = 0.0696/ √ E. To test the validity of the equation and to compare the results of the total attenuation coefficients of 3 tissue-equivalent materials (bolus, rice grains, and boiled rice) that could not be determined before, they were determined experimentally by using X-rays produced at 6 MV and 18 MV. The results of the experiment show a relatively good match with the computed values using the suggested equation. It is possible to conclude that 1) the suggested equation is a practical way to define the total attenuation coefficients of biological tissue or tissue-equivalent materials and 2) the attenuation coefficient is one of the most important to determine the absorbed dose by patients and so they should be worked out experimentally before treatment.

No abstract

In a medical linear accelerator, the primary and secondary collimators are generally made of high atomic weight metals. The energy of the x-rays generated by accelerated electrons exceeds the bonding energies of high atomic number materials such as tungsten, and lead in the structure of the components in the accelerator head, it causes the production of neutron from the nucleus. Consequently, the resulting photo-neutrons can easily be scattered and spread into the treatment room. Thus, an additional neutron dose cannot be ignored in the tumor volume of the patient and in areas outside this volume. The contribution of the primary and secondary collimators to the neutron contamination is found to be approximately 52% and 30%, respectively. In this paper, the effects of using different composite materials such as Boron, Cadmium, and Polyethylene in secondary collimators on neutron contamination have been investigated by using Fluka Monte Carlo and TALYS 1.9 codes

Abstract:The purpose of this investigation is to measure the total attenuation coefficients (TACs) of plaster materials using different geometries of the plaster, field sizes, and photon beam energies. The percent depth dose measurements were made using X-rays at 6 MV and 18 MV from the linear accelerator in order to plan the probable radiation dose to be given to the patient wearing a plaster cast. The TAC was experimentally determined in solid phantoms of various thicknesses both with and without plaster over areas of 5 × 5 cm 2 , 10 × 10 cm 2 , and 15 × 15 cm 2 . The experimentally measured TAC for plaster was compared to that of the NIST program. The TAC of solid phantom with plaster was found to be larger than without plaster. This means that d max is very close to the skin and that in these situations plaster has a bolus effect, increasing the skin's dose.

No abstract