Journal of the ICRU Vol 6 No 2 (2006) Report 76 Oxford University Press
doi:10.1093/jicru/ndl031
DEFINITIONS AND GLOSSARY OF TERMS
Absorbed dose, D, is the quotient of d « by dm, where d « is the mean energy imparted by ionizing radiation to matter of mass dm, thus D¼
d « : dm
Unit: J kg1 The special name for the unit of absorbed dose is gray (Gy). The absorbed dose rate, D_ , is the quotient of dD by dt. Accredited calibration laboratory is an organization disseminating standards traceable to primary standards and designated by an accrediting body as to their ability to meet metrological criteria (ISO/IEC, 1999). Accuracy of measurement is the closeness of the agreement between the result of a measurement and a true value of the measurand. Note: Accuracy is a qualitative concept. The term precision (see repeatability) should not be used in place of accuracy. Accuracy of a measuring instrument is the ability of a measuring instrument to give responses close to a true value (ISO/IEC, 1993). Arithmetic mean or the average, q, of individual observed values qj ( j ¼ 1, 2, . . ., n) is evaluated (ISO, 1995) using q ¼
n 1X qj : n j¼1
Calibration is a set of operations that establish, under specified conditions, the relationship between values indicated by a dosimetric device and the
corresponding known (i.e., conventionally true) values of the quantity to be measured (ISO, 1995). Indication (of a measuring instrument) is the value of a quantity provided by a measuring instrument (ISO/IEC, 1993). Note: The value read from the displaying device can be called the direct indication; it is multiplied by the instrument constant to give the indication. The quantity can be the measurand, a measurement signal, or another quantity to be used in calculating the value of the measurand. For a material measure, the indication is the value assigned to it. Instrument constant is the coefficient by which the direct indication of the measuring instrument must be multiplied to give the value of the measurand, or of a quantity to be used to calculate the value of the measurand (ISO/IEC, 1993). Calibration coefficient is the quotient of the conventional true value of the quantity to be measured and the direct indication of the instrument normalized to the reference conditions. The calibration coefficient is equivalent to the instrument constant multiplied by the calibration factor (ISO/IEC, 1993). Calibration factor is the factor by which the indication (direct indication multiplied by the instrument constant), of the device is multiplied to obtain the conventional true value of the quantity to be measured under reference conditions (ISO/IEC, 1993). Combined standard uncertainty is the standard uncertainty of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or covariances of these other quantities weighted according to how the measurement result varies with changes in these quantities (ISO, 1995). Conventional true value (of a quantity) is the value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainty appropriate for a given purpose (ISO/IEC, 1993). Coverage factor, k, is the numerical factor used as a multiplier of the combined standard
International Commission on Radiation Units and Measurements 2006
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
Definitions of dosimetric quantities can be found in ICRU Report 60 (ICRU, 1998), but several useful definitions will be reproduced here, for convenience, as are some terms taken from the International Vocabulary of Basic and General Terms in Metrology (VIM, 1993) and the Guide to the Expression of Uncertainty in Measurement (GUM, 1995). Additional terms are defined because they are used in the present report in specific contexts, and it is necessary to have precise definitions to avoid misinterpretation.
MEASUREMENT QUALITY ASSURANCE FOR IONIZING RADIATION DOSIMETRY
uncertainty, uc(y), in order to obtain the expanded uncertainty U. Note: U ¼ kuc ( y) (ISO, 1995).
Measurement assurance program is a process that quantifies the total uncertainty of measurements by means of comparison to national standards, and demonstrates that the uncertainty is appropriate for the intended use of the measurements (ISO, 2003).
Determination limit is the lowest (expectation) value of the quantity of interest that can be measured with a given fractional (percentage) uncertainty (ISO, 1995).
Measurement control system consists of a set of operations to confirm the quality of measuring equipment and measurement processes (ISO, 2003).
Direct indication of an instrument is the numerical value read from the displaying device; it can be multiplied by the instrument constant to give the indication (ISO/IEC, 1993).
Model function is a mathematical expression or algorithm used to determine a measurand (ISO, 1995). Normalization factor is the dimensionless parameter used to correct to reference conditions (ISO/IEC, 1993). Output estimate is an estimate of the measurand using an equation or model function and estimates of input quantities (ISO, 1995).
Experimental standard deviation is the standard deviation of the mean that follows from an averaging procedure or an appropriate regression analysis (ISO/IEC, 1993).
Output quantity is a quantity not measured directly, but is determined from N other quantities X1, X2,. . ., XN through a functional relationship (ISO, 1995).
Indication (of a measuring instrument) is the value of a quantity provided by a measuring instrument. Note: The indication (reading) is expressed in units of the measurand regardless of the units marked on the scale of the instrument. What appears on the scale has to be multiplied by the instrument constant to provide the indication (reading). It is necessary to document whether the indication (reading) is normalized to the reference conditions to account for influence quantities and is corrected for intrinsic background and other factors (ISO/IEC, 1993).
Point of test is the point in the radiation field at which the conventional true value of a quantity is known (ISO, 1995). Quality assurance can be defined as those planned and systematic actions necessary to provide adequate confidence that a structure, system, procedure, or component will perform satisfactorily and comply with agreed upon standards (ISO, 2003). Quality control consists of the set of operations intended to maintain or improve quality.
Influence quantity is a quantity that is not the measurand but that affects the result of the measurement (ISO/IEC, 1993).
Reading (see indication).
Input quantities are quantities X1, X2,. . ., XN upon which the output quantity Y depends (ISO, 1995).
Reference conditions are conditions of use prescribed for testing the performance of a measuring instrument or for comparison of results of measurements. Note: The reference conditions generally include reference values or reference ranges for the influence quantities affecting the measuring instrument (ISO/IEC, 1993).
Kerma, K, is the quotient of dEtr by dm, where dEtr is the sum of the initial kinetic energies of all the charged particles liberated by uncharged particles in a mass dm of material, thus dEtr K¼ : dm Unit: J kg1. The special name for the unit of kerma is gray (Gy). Note: The quantity dEtr includes the kinetic energy of Auger electrons.
Reference direction is the direction in the coordinate system of the dosimetric instrument with respect to which the angle of the direction of radiation is measured in unidirectional fields. Reference orientation of a dosimetric instrument is the orientation for which the direction of incident radiation coincides with the reference direction of the dosimeter.
Measurand is a particular quantity subject to measurement (ISO/IEC, 1993). 40
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
Expanded uncertainty, U, is the quantity defining an interval about the result of a measurement that can be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand. Note: y U Y y þ U, which is commonly written as Y ¼ y – U (ISO, 1995).
DEFINITIONS AND GLOSSARY OF TERMS Response (response characteristic) is the relationship between a stimulus and the corresponding output signal for defined conditions. Note: The input signal to a measuring system may be called the stimulus; the output signal may be called the response.
Reference point is the point on a dosimetric instrument that is placed at the point of test for calibration or test purposes. Reference standard is a measuring device of the highest metrological quality at the facility. Repeatability is the closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement. Note: These conditions are called repeatability conditions. Repeatability conditions include the same measurement procedure, the same observer, the same measuring instrument, used under the same conditions, the same location, and repetition over a short period of time. Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the results. Precision, although no longer the preferred word, has been used to mean repeatability (ISO/IEC, 1993).
Secondary standard dosimetry laboratory is an organization disseminating standards traceable to primary standards. Standard deviation, s Xi , or standard uncertainty, u(xi), is given as follows: "
n X 2 1 Xi;k Xi nðn 1Þ k¼1
#1=2 ,
where n is the number of independent observations of the quantity X (ISO, 1995). Standard test conditions are those represented by the range of values for the influence quantities under which a calibration or determination of the response is carried out. Appropriate corrections to reference conditions should be made.
Reproducibility (of results of measurements) is the closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement. Note: A valid statement of reproducibility requires specification of the conditions changed. The changed conditions can include principle of measurement, method of measurement, observer, measuring instrument, reference standard, location, conditions of use, or time. Reproducibility can be expressed quantitatively in terms of the dispersive characteristics of the results. Results are usually understood to be corrected results (ISO/IEC, 1993).
Sensitivity coefficient indicates the extent to which the output estimate is influenced by variations in the input estimate (ISO, 1995). Uncertainty (of measurement) is the parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (ISO, 1995).
41
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
s Xi ¼ uðxi Þ ¼
doi:10.1093/jicru/ndl031
DEFINITIONS AND GLOSSARY OF TERMS
Absorbed dose, D, is the quotient of d « by dm, where d « is the mean energy imparted by ionizing radiation to matter of mass dm, thus D¼
d « : dm
Unit: J kg1 The special name for the unit of absorbed dose is gray (Gy). The absorbed dose rate, D_ , is the quotient of dD by dt. Accredited calibration laboratory is an organization disseminating standards traceable to primary standards and designated by an accrediting body as to their ability to meet metrological criteria (ISO/IEC, 1999). Accuracy of measurement is the closeness of the agreement between the result of a measurement and a true value of the measurand. Note: Accuracy is a qualitative concept. The term precision (see repeatability) should not be used in place of accuracy. Accuracy of a measuring instrument is the ability of a measuring instrument to give responses close to a true value (ISO/IEC, 1993). Arithmetic mean or the average, q, of individual observed values qj ( j ¼ 1, 2, . . ., n) is evaluated (ISO, 1995) using q ¼
n 1X qj : n j¼1
Calibration is a set of operations that establish, under specified conditions, the relationship between values indicated by a dosimetric device and the
corresponding known (i.e., conventionally true) values of the quantity to be measured (ISO, 1995). Indication (of a measuring instrument) is the value of a quantity provided by a measuring instrument (ISO/IEC, 1993). Note: The value read from the displaying device can be called the direct indication; it is multiplied by the instrument constant to give the indication. The quantity can be the measurand, a measurement signal, or another quantity to be used in calculating the value of the measurand. For a material measure, the indication is the value assigned to it. Instrument constant is the coefficient by which the direct indication of the measuring instrument must be multiplied to give the value of the measurand, or of a quantity to be used to calculate the value of the measurand (ISO/IEC, 1993). Calibration coefficient is the quotient of the conventional true value of the quantity to be measured and the direct indication of the instrument normalized to the reference conditions. The calibration coefficient is equivalent to the instrument constant multiplied by the calibration factor (ISO/IEC, 1993). Calibration factor is the factor by which the indication (direct indication multiplied by the instrument constant), of the device is multiplied to obtain the conventional true value of the quantity to be measured under reference conditions (ISO/IEC, 1993). Combined standard uncertainty is the standard uncertainty of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or covariances of these other quantities weighted according to how the measurement result varies with changes in these quantities (ISO, 1995). Conventional true value (of a quantity) is the value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainty appropriate for a given purpose (ISO/IEC, 1993). Coverage factor, k, is the numerical factor used as a multiplier of the combined standard
International Commission on Radiation Units and Measurements 2006
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
Definitions of dosimetric quantities can be found in ICRU Report 60 (ICRU, 1998), but several useful definitions will be reproduced here, for convenience, as are some terms taken from the International Vocabulary of Basic and General Terms in Metrology (VIM, 1993) and the Guide to the Expression of Uncertainty in Measurement (GUM, 1995). Additional terms are defined because they are used in the present report in specific contexts, and it is necessary to have precise definitions to avoid misinterpretation.
MEASUREMENT QUALITY ASSURANCE FOR IONIZING RADIATION DOSIMETRY
uncertainty, uc(y), in order to obtain the expanded uncertainty U. Note: U ¼ kuc ( y) (ISO, 1995).
Measurement assurance program is a process that quantifies the total uncertainty of measurements by means of comparison to national standards, and demonstrates that the uncertainty is appropriate for the intended use of the measurements (ISO, 2003).
Determination limit is the lowest (expectation) value of the quantity of interest that can be measured with a given fractional (percentage) uncertainty (ISO, 1995).
Measurement control system consists of a set of operations to confirm the quality of measuring equipment and measurement processes (ISO, 2003).
Direct indication of an instrument is the numerical value read from the displaying device; it can be multiplied by the instrument constant to give the indication (ISO/IEC, 1993).
Model function is a mathematical expression or algorithm used to determine a measurand (ISO, 1995). Normalization factor is the dimensionless parameter used to correct to reference conditions (ISO/IEC, 1993). Output estimate is an estimate of the measurand using an equation or model function and estimates of input quantities (ISO, 1995).
Experimental standard deviation is the standard deviation of the mean that follows from an averaging procedure or an appropriate regression analysis (ISO/IEC, 1993).
Output quantity is a quantity not measured directly, but is determined from N other quantities X1, X2,. . ., XN through a functional relationship (ISO, 1995).
Indication (of a measuring instrument) is the value of a quantity provided by a measuring instrument. Note: The indication (reading) is expressed in units of the measurand regardless of the units marked on the scale of the instrument. What appears on the scale has to be multiplied by the instrument constant to provide the indication (reading). It is necessary to document whether the indication (reading) is normalized to the reference conditions to account for influence quantities and is corrected for intrinsic background and other factors (ISO/IEC, 1993).
Point of test is the point in the radiation field at which the conventional true value of a quantity is known (ISO, 1995). Quality assurance can be defined as those planned and systematic actions necessary to provide adequate confidence that a structure, system, procedure, or component will perform satisfactorily and comply with agreed upon standards (ISO, 2003). Quality control consists of the set of operations intended to maintain or improve quality.
Influence quantity is a quantity that is not the measurand but that affects the result of the measurement (ISO/IEC, 1993).
Reading (see indication).
Input quantities are quantities X1, X2,. . ., XN upon which the output quantity Y depends (ISO, 1995).
Reference conditions are conditions of use prescribed for testing the performance of a measuring instrument or for comparison of results of measurements. Note: The reference conditions generally include reference values or reference ranges for the influence quantities affecting the measuring instrument (ISO/IEC, 1993).
Kerma, K, is the quotient of dEtr by dm, where dEtr is the sum of the initial kinetic energies of all the charged particles liberated by uncharged particles in a mass dm of material, thus dEtr K¼ : dm Unit: J kg1. The special name for the unit of kerma is gray (Gy). Note: The quantity dEtr includes the kinetic energy of Auger electrons.
Reference direction is the direction in the coordinate system of the dosimetric instrument with respect to which the angle of the direction of radiation is measured in unidirectional fields. Reference orientation of a dosimetric instrument is the orientation for which the direction of incident radiation coincides with the reference direction of the dosimeter.
Measurand is a particular quantity subject to measurement (ISO/IEC, 1993). 40
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
Expanded uncertainty, U, is the quantity defining an interval about the result of a measurement that can be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand. Note: y U Y y þ U, which is commonly written as Y ¼ y – U (ISO, 1995).
DEFINITIONS AND GLOSSARY OF TERMS Response (response characteristic) is the relationship between a stimulus and the corresponding output signal for defined conditions. Note: The input signal to a measuring system may be called the stimulus; the output signal may be called the response.
Reference point is the point on a dosimetric instrument that is placed at the point of test for calibration or test purposes. Reference standard is a measuring device of the highest metrological quality at the facility. Repeatability is the closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement. Note: These conditions are called repeatability conditions. Repeatability conditions include the same measurement procedure, the same observer, the same measuring instrument, used under the same conditions, the same location, and repetition over a short period of time. Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the results. Precision, although no longer the preferred word, has been used to mean repeatability (ISO/IEC, 1993).
Secondary standard dosimetry laboratory is an organization disseminating standards traceable to primary standards. Standard deviation, s Xi , or standard uncertainty, u(xi), is given as follows: "
n X 2 1 Xi;k Xi nðn 1Þ k¼1
#1=2 ,
where n is the number of independent observations of the quantity X (ISO, 1995). Standard test conditions are those represented by the range of values for the influence quantities under which a calibration or determination of the response is carried out. Appropriate corrections to reference conditions should be made.
Reproducibility (of results of measurements) is the closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement. Note: A valid statement of reproducibility requires specification of the conditions changed. The changed conditions can include principle of measurement, method of measurement, observer, measuring instrument, reference standard, location, conditions of use, or time. Reproducibility can be expressed quantitatively in terms of the dispersive characteristics of the results. Results are usually understood to be corrected results (ISO/IEC, 1993).
Sensitivity coefficient indicates the extent to which the output estimate is influenced by variations in the input estimate (ISO, 1995). Uncertainty (of measurement) is the parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (ISO, 1995).
41
Downloaded from http://jicru.oxfordjournals.org/ at University of Oklahoma on August 24, 2014
s Xi ¼ uðxi Þ ¼
