The International Commission on Radiation Units and Measurements (ICRU) has had for some time a Standing Committee on Fundamental Quantities and Units, which in 2011 produced Report No. 85a on Fundamental Quantities and Units for Ionizing Radiation, an update of ICRU Report No. 60. In order to address the issues of overlap in the quantities and terminology used in reports on radiation therapy and to ensure uniformity in usage a Standing Committee on Terminology, Quantities, and Units in Radiation Therapy was established in 2013.
Protection of personnel working with radiation relies on careful measurement. The protection of the public and the environment depends on evaluation of radiation and radioactive materials in the environment. Because of diversity in exposures in both routine and accident conditions, internationally accepted measurement conventions are required for assessment of irradiation of individuals and for monitoring of the environment. Specialized quantities and a substantial collection of reference data are needed for correlation of individual exposures and the associated risks. ICRU developed a conceptual basis for the definition of operational quantities for area and individual monitoring in the reports Determination of Dose Equivalents Resulting from External Radiation Sources, Part 1, Report No. 39 (1985), and Part 2, Report No. 43 (1988). These quantities are used in measurements and calculations for the assessment of compliance with exposure limitations. In 1993, Report No. 51, Quantities and Units in Radiation Protection Dosimetry, updated the definitions of the operational quantities, taking account of recommendations published by the International Commission on Radiological Protection (ICRP) in 1990. Guidance for the measurement of operational quantities was provided in Report No. 47 (1992) and Report No. 66 (2001). In 1998 ICRU published Report No. 57, Conversion Coefficients for Use in Radiological Protection against External Radiation, facilitating conversion between operational and protection quantities. An update, Dose Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposure, has been prepared in conjunction with, and published as ICRP Publication 116 (2010). Environmental measurements were treated in Report 53 (1994), Gamma-Ray Spectrometry in the Environment, Report No. 65 (2001), Quantities, Units, and Terms in Radioecology, and in Report No. 75 (2006), Sampling for Radionuclides in the Environment. Beta-ray measurements were covered in Report No. 56 (1997), Dosimetry of External Beta Rays for Radiation Protection. Recently published were Report No. 84 (2010), Reference Data for the Validation of Doses from Cosmic-Radiation Exposure of Aircraft Crew, and Report No. 86 (2011) Quantification and Reporting of Low-Dose and Other Heterogeneous Exposures. A new report on Operational Radiation Protection Quantities for External Radiation [replacing Report No. 51(1993) and, in part, Report No. 57 (1998)] will take into account changes in the definitions of the quantities, and the fields of application. As a result of problems encountered with the mapping of radioactive contamination following the Fukushima nuclear catastrophe in 2011, an important report on Monitoring and Assessment of Radiation Releases to the Environment has been initiated. Funding for this work has been provided by the U.S. Environmental Protection Agency (EPA).
Three topical areas are fundamental from the point of view of basic science. First, quantities and units of radiation and radioactivity should be defined clearly and sensibly for effective communication. Second, techniques and instruments for radiation measurements need to be standardized for optimal performance. Third, basic physical data concerning interactions of radiation with matter must be established optimally in the light of the latest scientific results and updated continuously. These data are necessary in research on mechanisms of physical, chemical, and biological changes induced by radiation, as well as in application to medicine, industry, and radiation risk assessment. ICRU has been continuously studying all three of these areas and, from time to time, has issued results of its studies in many reports. Subject matter treated in the reports include: radiation quantities and units in Report Nos. 51 (1993), 65 (2001) and 85a (2011); dosimetric techniques and instrumentation in Report Nos. 34 (1982) , 36 (1983), 44 (1989), 48 (1992), 57 (1998), 61 (1998), 69 (2003), and 76 (2006), stopping powers of particles of radiological and dosimetric importance [Report No. 37 (electrons and positrons), Report No. 49 (protons), and Report No. 73 (ions heavier than helium) (ICRU, 1984; 1993; 2005)] and other radiation interaction data [Report Nos. 31 (1979), 46 (1992), 55 (1995), and 63 (2000)]. Report No. 64 (2001) described Dosimetry of High-Energy Photon Beams based on Standards of Absorbed Dose to Water; Report No. 65 (2001) treated Quantities, Units, and Terms in Radioecology; Report No. 77 (2007) provided comprehensive information on Elastic Scattering of Electrons and Positrons; and Report No. 76 (2006) discussed Measurement Quality Assurance for Ionizing Radiation Dosimetry. Report No. 80 on Dosimetry Systems for Use in Radiation Processing was published in 2008. An updated report on Fundamental Quantities and Units has been completed and published, after revision, as Report No. 85a (2011). A report on Key Data for Measurement Standards in the Dosimetry of Ionizing Radiation is currently being prepared. It is difficult to compare or combine patient doses delivered with different beam qualities and under different conditions. A report committee to compile a report on Bioeffect Modeling and Equieffective Dose Concepts in Radiation Therapy has recently been established and will address the issues involved and propose a uniform methodology. The naturally occurring radioactive gas radon is a major source of public exposure to ionizing radiation. Radon can accumulate in buildings and can cause lung cancer. A new report on Measurement and Reporting of Radon Exposures has reached an advanced stage of publication. A report on Adult Reference Computational Phantoms has been compiled in conjunction with ICRP and published as ICRP Publication 110 (2009).
Diagnostic Radiology and Nuclear Medicine
Radiation is essential in modern medicine for diagnosis and clinical management of many kinds of illness. Diagnostic imaging has become increasingly complex, and manipulation of image information requires common concepts, terminology, and measurement methodology. This is essential for the benefit of the patient to ensure maximum diagnostic information with minimum potential risk. ICRU prepared two reports on subjects related to modern medical imaging, Modulation Transfer Function of Screen-Film Systems (Report No. 41) in 1986 and Medical Imaging – Assessment of Image Quality (Report No. 54) in 1995. These provided a theoretical framework on image quality and evaluation of medical imaging systems, including conventional and digital radiography, computed tomography (CT), nuclear medical imaging, magnetic resonance imaging (MRI), and ultrasonography. Report No. 61 (1998) on Tissue Substitutes, Phantoms, and Computational Modeling in Medical Ultrasound, Report No. 67 (2002) on Absorbed Dose Specification in Nuclear Medicine, and Report No. 70 (2003) on Image Quality in Chest Radiography followed. More recently Report No. 74 (2005) on Patient Dosimetry of X Rays used in Medical Imaging was published. Report Nos. 67 and 74 addressed the issue of dose assessment in radiodiagnosis, which is of increasing concern as the average number of diagnostic procedures per capita is increasing. Reports on Receiver Operator Characteristic (ROC) Analysis in Medical Imaging (Report No. 79, 2008), Quantitative Aspects of Bone Densitometry (Report No. 81, 2009), Mammography: Assessment of Image Quality (Report No. 82, 2009), and Image Radiation Dose and Image Quality Assessment in Computed Tomography (Report No. 87, 2012) have recently been published. ICRU is also considering undertaking new reports covering state-of-the-art imaging techniques (e.g., functional and molecular imaging) which are rapidly expanding and finding increasing use diagnosis and in staging tumors and in planning and delivering radiation therapy treatments.
The successful radiation treatment of cancer depends vitally on knowledge of the precise amount and location of radiation given to a patient and the opportunity for therapists to exchange this information and the results achieved. As far as radiation measurement is concerned, ICRU published several early reports recommending dosimetry protocols for photon and electron-beam therapy [Report Nos. 17 (1970), 23 (1973), and 24 (1976)] and later for new types of radiations. In that respect, Report No. 45 (1989) dealt with clinical dosimetry for fast neutrons, and a similar report with protons [Report No. 59 (1998)]. Report No. 64 (2001) updated the dosimetry of high-energy photon beams. Fundamental data for radiation therapy were covered in Report No. 37 (1984) on Stopping Powers for Electrons and Positrons, Report No. 49 on Stopping Powers and Ranges of Protons and Alpha Particles, and Report No. 73 (2005) on Stopping of Ions Heavier than Helium. Report No. 72 (2004) discussed Dosimetry of Beta Rays and Low-Energy Photons for Brachytherapy with Sealed Sources. Progress in radiation therapy requires the ability to compare clinical results achieved in different centers using different radiation modalities and protocols. Thus a common language for reporting fractionation schedules, doses, and techniques is required for optimum treatment. ICRU has devoted considerable effort in that direction. Report No. 50 (1993) on Prescribing, Recording, and Reporting Photon-Beam Therapy provides appropriate guidance for defining tumor, target and planning volumes and gives recommendations for complete reporting of photon treatments. A supplement, published as Report No. 62 (1999), brought these recommendations up to date. The concepts and definitions in these latter reports remain the basis of reports adapting these principles to a series of reports on Prescribing, Recording, and Reporting different therapies: Electron-Beam Therapy [Report No. 71 (2004)], Proton-Beam Therapy [Report No. 78 (2007) – joint report with International Atomic Energy Agency (IAEA)], Intensity-Modulated Photon-Beam Therapy (IMRT) [Report No. 83 (2010)]. Three additional reports in the series are in preparation: Ion-beam Beam Therapy, Stereotactic Treatments with Small Photon Beams and Brachytherapy for Cancer of the Cervix. The latter report will update the report on Dose and Volume Specification for Reporting Intracavitary Therapy in Gynecology [Report No.38 (1985)]. A similar report on Dose and Volume Specification for Reporting Interstitial Therapy was published as Report No. 58 (1997). Many of the methods of prescribing, recording, and reporting doses and volumes are common to all therapy modalities. To ensure uniform application, a joint report with the American Association of Physicists in Medicine and Biology (AAPM) encompassing the definitions and terminologies used in all techniques is under consideration. Other possible new reports concern the induction of secondary malignancies and use of internal emitters in radiation therapy.
The responsibility of ICRU remains unchanged; namely, providing internationally- acceptable recommendations concerning concepts, quantities, units, and measurement procedures for users of ionizing radiation in medicine, basic science, industry, environment and radiation protection. ICRU endeavors to collect and evaluate the latest data and information pertinent to the problems of radiation measurement, and to recommend in its publications the most appropriate values of radiation quantities and the most acceptable and safest techniques for current use. These recommendations are constantly reviewed and extended in accordance with the rapid developments in radiation medicine, science, and technology. In radiation protection, ICRU has introduced operational quantities and recommendations for their experimental determination. In basic science, the measurement of physical parameters concerning ionizing radiation is improving constantly, and the results must be continuously re-evaluated in order to provide recommendations on reducing the risk of radiation exposure by both the public and radiation workers. In diagnostic radiology and nuclear medicine, these developments have been rapid, and ICRU has expanded its program related to medical imaging, ranging from fundamental concepts to practical applications involving all types of imaging techniques, and also encompassing specific dosimetric procedures regarding protection. In radiation therapy, the current ICRU program has focused much attention on specification of volumes and doses for reporting and has extended its program to newer types of therapy for which the spatial distributions of absorbed dose need to be known more precisely. ICRU is always receptive to suggestions from the scientific and medical communities for new initiatives.