Biomaterial Database

Computer calculation of the dose distribution in the electron build-up region. 1980

J M Galvin, and R E Wallace, and P Bloch, and E Cheng

A procedure has been developed for producing accurate computer-calculated dose distributions at the air-tissue boundaries for oblique incidence of a photon beam. Measurements of the dose distribution under conditions of tangential incidence are presented for a Siemens 6 MV linear accelerator. These measurements have been compared with calculated distributions using the standard Cunningham-Clarkson calculation technique. Based on this comparison, two changes are suggested for improving the accuracy of the calculation. The grid spacing for the calculation is decreased in order that the rapid dose variations that occur at the boundary may be better followed. Furthermore, the dose calculation scheme is modified to take into account the differences in the amount of electron build-up which occurs. An algorithm is presented for making this modification. Also, the calculated dose at the exit surface had to be modified to handle the deficit of scatter material behind the calculation points. The results of these changes are shown as a comparison of a typical chest wall irradiation treatment plan using two opposing tangential fields.

UI	MeSH Term	Description	Entries
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D010315	Particle Accelerators	Devices which accelerate electrically charged atomic or subatomic particles, such as electrons, protons or ions, to high velocities so they have high kinetic energy.	Betatrons,Linear Accelerators,Accelerator, Linear,Accelerator, Particle,Accelerators, Linear,Accelerators, Particle,Betatron,Linear Accelerator,Particle Accelerator
D011522	Protons	Stable elementary particles having the smallest known positive charge, found in the nuclei of all elements. The proton mass is less than that of a neutron. A proton is the nucleus of the light hydrogen atom, i.e., the hydrogen ion.	Hydrogen Ions,Hydrogen Ion,Ion, Hydrogen,Ions, Hydrogen,Proton
D011829	Radiation Dosage	The amount of radiation energy that is deposited in a unit mass of material, such as tissues of plants or animal. In RADIOTHERAPY, radiation dosage is expressed in gray units (Gy). In RADIOLOGIC HEALTH, the dosage is expressed by the product of absorbed dose (Gy) and quality factor (a function of linear energy transfer), and is called radiation dose equivalent in sievert units (Sv).	Sievert Units,Dosage, Radiation,Gray Units,Gy Radiation,Sv Radiation Dose Equivalent,Dosages, Radiation,Radiation Dosages,Units, Gray,Units, Sievert
D003201	Computers	Programmable electronic devices designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations.	Calculators, Programmable,Computer Hardware,Computers, Digital,Hardware, Computer,Calculator, Programmable,Computer,Computer, Digital,Digital Computer,Digital Computers,Programmable Calculator,Programmable Calculators
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012867	Skin	The outer covering of the body that protects it from the environment. It is composed of the DERMIS and the EPIDERMIS.

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