Joint ICTP-IAEA Workshop on Determination of Uncertainties of Measurements in Medical Radiation Dosimetry | (smr 2616)
Starts 9 Jun 2014
Ends 13 Jun 2014
Central European Time
LB (Euler Lecture Hall)
Strada Costiera, 11
I - 34151 Trieste (Italy)
The aim of this Workshop is to familiarize physicists, working in radiation dosimetry laboratories or lecturers teaching radiation dosimetry, with procedures and methodologies that should be utilized for the determination of uncertainties in medical radiation dosimetry.
Contrary to earlier practice, when the terms error and uncertainty were used interchangeably, the modern approach distinguishes between these two concepts. Traditionally, an error has been viewed as having two components, namely a random component and a systematic component. According to present definitions, an error is the difference between a measured value and the true value. If errors were known exactly, the true value could be determined; in reality, errors are estimated in the best possible way and corrections are made for them. Therefore, after application of all known corrections, errors do not need any further consideration and the quantities of interest are uncertainties. An error has both a numerical value and a sign. In contrast, the uncertainty associated with a measurement is a parameter that characterizes the dispersion of the values “that could reasonably be attributed to the measurand”.
This parameter is normally an estimated standard deviation. An uncertainty, therefore, has no known sign and is usually assumed to be symmetrical. It is “a measure” of our lack of exact knowledge, after all recognized systematic effects have been taken into count by applying appropriate corrections.
Uncertainties of measurements are expressed as relative standard uncertainties and the evaluation of standard uncertainties is classified into type A and type B. The method of evaluation of type A standard uncertainties is by statistical analysis of a series of observations, whereas the method of evaluation of type B standard uncertainties is based on means other than statistical analysis of a series of observations.
The IAEA, understanding the need to provide practical guidance on the estimation of measurement uncertainty in dosimetry, has incorporated a specific section on this topic in relevant publications on radiation dosimetry, such as the IAEA TRS-398 (Absorbed Dose Determination in External-Beam Radiotherapy An-International Code of Practice for Dosimetry Based on Standards of Absorbed dose toWater), IAEA TRS-454 (Quality Assurance for Radioactivity Measurement in Nuclear Medicine), IAEA TRS-457 (Dosimetry in Diagnostic Radiology: An International Code of Practice) and IAEA TEC DOC-1585 Measurement Uncertainty: A Practical Guide for Secondary-Standards Dosimetry Laboratories).