Biomaterial Database

Calibration in water versus calibration in air for cobalt-60 gamma rays. 1977

W H Grant, and J H Cundiff, and W F Gagnon, and W F Hanson, and R J Shalek

In the United States it is common practice to calibrate Cobalt-60 teletherapy machines "in air," despite recommendations by the International Commission on Radiation Units and Measurements (ICRU) and other organizations that calibration be accomplished by measurement at 5-cm depth in a water phantom. A comparison has been made between the results of ionization measurements in air at 80.5-cm distance from the source and in water at 80-cm source-skin distance (SSD) for the determination of absorbed dose at three depth (5, 10, and 15 cm) for each of three fields sizes (6 X 6, 10 X 10, and 20 X 20 cm2), for a total of 42 Cobalt-60 machines. The mean of the ratio, absorbed dose from in-water measurements to absorbed dose at the same depth calculated from in-air measurements, ranged frt 5-cm depth for a 20 X 20-cm2 field size. Reasons for the differences are offered, and compliance with ICRU recommendations is suggested.

UI	MeSH Term	Description	Entries
D011839	Radiation, Ionizing	ELECTROMAGNETIC RADIATION or particle radiation (high energy ELEMENTARY PARTICLES) capable of directly or indirectly producing IONS in its passage through matter. The wavelengths of ionizing electromagnetic radiation are equal to or smaller than those of short (far) ultraviolet radiation and include gamma and X-rays.	Ionizing Radiation,Ionizing Radiations,Radiations, Ionizing
D011867	Radioisotope Teletherapy	A type of high-energy radiotherapy using a beam of gamma-radiation produced by a radioisotope source encapsulated within a teletherapy unit.	Teleradioisotope Therapy,Teletherapy, Radioisotope,Therapy, Teleradioisotope
D011879	Radiotherapy Dosage	The total amount of radiation absorbed by tissues as a result of radiotherapy.	Dosage, Radiotherapy,Dosages, Radiotherapy,Radiotherapy Dosages
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
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
D000388	Air	The mixture of gases present in the earth's atmosphere consisting of oxygen, nitrogen, carbon dioxide, and small amounts of other gases.
D014867	Water	A clear, odorless, tasteless liquid that is essential for most animal and plant life and is an excellent solvent for many substances. The chemical formula is hydrogen oxide (H2O). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)	Hydrogen Oxide