Biomaterial Database

Electron contamination from different materials in high energy photon beams. 1985

B Nilsson

Relative lateral electron surface dose distributions from filters and air in high energy photon beams were determined using the Fermi-Eyges theory of multiple scattering. The model includes transmission and angular scattering in materials and in air. Backscatter from the phantom was also estimated. The variation of surface dose with different parameters such as atomic number, thickness and position of material, field size and photon energy was investigated. The calculated data show good agreement with experiment. For 60Co gamma rays, electron filters of medium atomic number give the lowest surface dose, whereas for higher energies a low to medium atomic number material should be used, especially for short material-phantom distances and large field sizes. The contribution to surface dose can be reduced by over 30% by placing a thin foil of high atomic number after a low to medium atomic number filter, thus scattering some electrons from the beam. For 60Co gamma rays the air is often the dominant source of contaminating electrons because of high multiple scatter loss at this energy, while for higher photon energies the beam flattening filter is the main electron source because of the small emission angle of the electrons and the small scattering power at high energies.

UI	MeSH Term	Description	Entries
D008961	Models, Structural	A representation, generally small in scale, to show the structure, construction, or appearance of something. (From Random House Unabridged Dictionary, 2d ed)	Model, Structural,Structural Model,Structural Models
D011879	Radiotherapy Dosage	The total amount of radiation absorbed by tissues as a result of radiotherapy.	Dosage, Radiotherapy,Dosages, Radiotherapy,Radiotherapy Dosages
D011882	Radiotherapy, High-Energy	Radiotherapy using high-energy (megavolt or higher) ionizing radiation. Types of radiation include gamma rays, produced by a radioisotope within a teletherapy unit; x-rays, electrons, protons, alpha particles (helium ions) and heavy charged ions, produced by particle acceleration; and neutrons and pi-mesons (pions), produced as secondary particles following bombardment of a target with a primary particle.	Megavolt Radiotherapy,High-Energy Radiotherapy,Radiotherapy, Megavolt,High Energy Radiotherapy,Radiotherapy, High Energy
D003037	Cobalt Radioisotopes	Unstable isotopes of cobalt that decay or disintegrate emitting radiation. Co atoms with atomic weights of 54-64, except 59, are radioactive cobalt isotopes.	Radioisotopes, Cobalt
D004583	Electrons	Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS.	Fast Electrons,Negatrons,Positrons,Electron,Electron, Fast,Electrons, Fast,Fast Electron,Negatron,Positron
D005720	Gamma Rays	Penetrating, high-energy electromagnetic radiation emitted from atomic nuclei during NUCLEAR DECAY. The range of wavelengths of emitted radiation is between 0.1 - 100 pm which overlaps the shorter, more energetic hard X-RAYS wavelengths. The distinction between gamma rays and X-rays is based on their radiation source.	Gamma Wave,Gamma Radiation,Nuclear X-Rays,Radiation, Gamma,X-Rays, Nuclear,Gamma Radiations,Gamma Ray,Gamma Waves,Nuclear X Rays,Nuclear X-Ray,Ray, Gamma,Wave, Gamma,Waves, Gamma,X Rays, Nuclear,X-Ray, Nuclear
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D013679	Technology, Radiologic	The application of scientific knowledge or technology to the field of radiology. The applications center mostly around x-ray or radioisotopes for diagnostic and therapeutic purposes but the technological applications of any radiation or radiologic procedure is within the scope of radiologic technology.	Radiologic Technology,Technology, Radiological,Radiological Technology
D014965	X-Rays	Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard X-rays are the higher energy, shorter wavelength X-rays. Soft x-rays or Grenz rays are less energetic and longer in wavelength. The short wavelength end of the X-ray spectrum overlaps the GAMMA RAYS wavelength range. The distinction between gamma rays and X-rays is based on their radiation source.	Grenz Ray,Grenz Rays,Roentgen Ray,Roentgen Rays,X Ray,X-Ray,Xray,Radiation, X,X-Radiation,Xrays,Ray, Grenz,Ray, Roentgen,Ray, X,Rays, Grenz,Rays, Roentgen,Rays, X,X Radiation,X Rays,X-Radiations