Editorial
Editorial Conversion to SI Units: Comment on the Special Report from the ICRU William R. Eyler, M.D. While conversion from the rad to the gray and from the curie to the becquerel poses no logistic difficulties, abandonment of the roentgen in favor of the SI unit "coulombs per kilogram" may take some getting used to. However, following consistently the logic of the International System of Units, the reasoning behind the recommended change is apparent; one roentgen equals 2.58 X 10- 4 coulombs per kilogram. INDEX TERMS: Editorials. International Commission on Radiation Units and Measurements (ICRU) • Radiations, measurement. Radiology and Radiologists Radiology 118:235, January 1976
• In a special report in this issue, the International Commission on Radiation Units and Measurements recommends that the rad, roentgen, and curie be gradually abandoned over a period of not less than 10 years (1). While the gray and the becquerel are straightforward conversions, I find a little more difficulty in adapting to the concept of coulombs per kilogram replacing the roentgen, whose definition I have carried around since residency years. I sought help from Dr. Harold Wyckoff, because it seemed to me that coulombs per kilogram did not quite equate with my concept of "exposure." Harold gave me the background that a decade or two ago, authorities had compromised and agreed to call the quantity "exposure dose"; but because of a tendency to confuse this term with "absorbed dose," it was shortened to "exposure." However, since we determine
the number of roentgens by measuring the ionization produced in electrostatic units and dividing it by the mass of air in the irradiated volume, we do the same thing when we determine the charge produced by this ionization in coulombs per unit of mass and obtain coulombs per kilogram. On this basis, one roentgen is equal to 2.58 X 10- 4 coulombs per kilogram, and this is our conversion factor. Department of Radiology Henry Ford Hospital Detroit, Mich. 48202
REFERENCE 1. Wyckoff HO, Allisy A, Liden K: The new special names of SI units in the field of ionizing radiations. Special report from the ICRU. Radiology 118:233-234, January 1976
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Editorial Conversion to SI Units: Comment on the Special Report from the ICRU William R. Eyler, M.D. While conversion from the rad to the gray and from the curie to the becquerel poses no logistic difficulties, abandonment of the roentgen in favor of the SI unit "coulombs per kilogram" may take some getting used to. However, following consistently the logic of the International System of Units, the reasoning behind the recommended change is apparent; one roentgen equals 2.58 X 10- 4 coulombs per kilogram. INDEX TERMS: Editorials. International Commission on Radiation Units and Measurements (ICRU) • Radiations, measurement. Radiology and Radiologists Radiology 118:235, January 1976
• In a special report in this issue, the International Commission on Radiation Units and Measurements recommends that the rad, roentgen, and curie be gradually abandoned over a period of not less than 10 years (1). While the gray and the becquerel are straightforward conversions, I find a little more difficulty in adapting to the concept of coulombs per kilogram replacing the roentgen, whose definition I have carried around since residency years. I sought help from Dr. Harold Wyckoff, because it seemed to me that coulombs per kilogram did not quite equate with my concept of "exposure." Harold gave me the background that a decade or two ago, authorities had compromised and agreed to call the quantity "exposure dose"; but because of a tendency to confuse this term with "absorbed dose," it was shortened to "exposure." However, since we determine
the number of roentgens by measuring the ionization produced in electrostatic units and dividing it by the mass of air in the irradiated volume, we do the same thing when we determine the charge produced by this ionization in coulombs per unit of mass and obtain coulombs per kilogram. On this basis, one roentgen is equal to 2.58 X 10- 4 coulombs per kilogram, and this is our conversion factor. Department of Radiology Henry Ford Hospital Detroit, Mich. 48202
REFERENCE 1. Wyckoff HO, Allisy A, Liden K: The new special names of SI units in the field of ionizing radiations. Special report from the ICRU. Radiology 118:233-234, January 1976
235
