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 assure maximum diagnostic information with minimum potential risk. The ICRU prepared two reports on subjects related to modern medical imaging, Modulation Transfer Function of Screen-Film Systems (Report 41) in 1986 and Medical Imaging - Assessment of Image Quality (Report 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 61 (1998) on Tissue Substitutes, Phantoms, and Computational Modeling in Medical Ultrasound, Report 67 (2002) on Absorbed Dose Specification in Nuclear Medicine, and Report 70 (2003) on Image Quality in Chest Radiography followed. More recently Report 74 (2005) on Patient Dosimetry of X Rays used in Medical Imaging was published. Reports 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 79, 2008), Quantitative Aspects of Bone Densitometry (Report 81, 2009) and Mammography: Assessment of Image Quality (Report 82, 2009) have recently been published.
The ICRU is also considering undertaking new reports covering state-of-the-art imaging techniques, viz., functional and molecular imaging, which are rapidly expanding and finding increasing use in staging tumors and planning radiation therapy treatments.
Radiation Therapy
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, the ICRU published several early reports recommending dosimetry protocols for photon and electron-beam therapy [Reports 17 (1970), 23 (1973), and 24 (1976)] and later for new types of radiations. In that respect, ICRU Report 45 (1989) dealt with clinical dosimetry for fast neutrons, and a similar report with protons [ICRU Report 59 (1998)]. ICRU Report 64 (2001) updated the dosimetry of high-energy photon beams. Fundamental data for radiation therapy were covered in Report 37 (1984) on Stopping Powers for Electrons and Positrons, Report 49 on Stopping Powers and Ranges of Protons and Alpha Particles, and Report 73 (2005) on Stopping of Ions Heavier than Helium. ICRU Report 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. The ICRU has devoted considerable effort in that direction. Report 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 ICRU Report 62 (1999), brings these recommendations up to date with current practice. The concepts and definitions in this report remain the basis of reports adapting these principles to electrons [ICRU Report 71 (2004)], protons [ICRU Report 78 (2007)] and to reports on Prescribing, Recording, and Reporting Intensity-Modulated Photon-Beam Therapy (IMRT) (to be published in 2010) and Prescribing, Recording, and Reporting Ion-beam Beam Therapy (in preparation). Similar reports have been published for intracavitary therapy in gynecology [Report 38 (1985)]: an update is currently in preparation; and for interstitial therapy [Report 58 (1997)].
Many of the methods of prescribing, recording, and reporting are common to all therapy modalities. A generic report on Harmonization of Prescribing, Recording, and Reporting Radiotherapy has been initiated.
Radiation Protection
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 risk.
The 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 39 (1985), and Part 2, Report 43 (1988). These quantities are used in measurements and calculations for the assessment of compliance with exposure limitations. In 1993, Report 51, Quantities and Units in Radiation Protection Dosimetry, updated the definitions of the operational quantities, taking account of recommendations published by the ICRP in 1990. Guidance for the measurement of operational quantities was provided in ICRU Report 47 (1992). In 1998 the ICRU published Report 57, Conversion Coefficients for Use in Radiological Protection against External Radiation, facilitating conversion between operational and protection quantities.
Environmental measurements were treated in Report 53 (1994), Gamma-Ray Spectrometry in the Environment, Report 65 (2001), Quantities, Units, and Terms in Radioecology, and in Report 75 (2006), Sampling for Radionuclides in the Environment.
Beta-ray measurements were covered in ICRU Report 56 (1997), Dosimetry of External Beta Rays for Radiation Protection. Recently published were Report 66 (2001), Determination of Operational Dose-Equivalent Quantities for Neutrons, Report 68 (2002), Retrospective Assessment of Exposure to Ionizing Radiation, and Report 69 (2003), Direct Determination of the Body Content of Radionuclides. A joint ICRP/ICRU report on Adult Reference Computational Phantoms has recently been published as ICRP Publication 110, 2009.
Reports on Alternatives to Absorbed Dose for Quantification of Low Fluence and Other Inhomogeneous Exposures and Reference Data for the Validation of Doses from Cosmic-Radiation Exposure of Aircraft Crew, and are currently nearing completion. A new report on Operational Radiation Protection Quantities for External Radiation [replacing ICRU Report 51(1993) and, in part, ICRU Report 57 (1998)] will take into account the changes in the definitions of the quantities, and the changes in the fields of application.
Radiation in Science
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.
The 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 Reports 51 (1993), 60 (1998), and 65 (2001); dosimetric techniques and instrumentation in Reports 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 [ICRU Report 37 (electrons and positrons), Report 49 (protons), and Report 73 (ions heavier than helium) (ICRU, 1984; 1993; 2005)] and other radiation interaction data [Reports 31 (1979), 46 (1992), 55 (1995), and 63 (2000)].
Report 64 (2001) described Dosimetry of High-Energy Photon Beams based on Standards of Absorbed Dose to Water; Report 65 (2001) treated Quantities, Units, and Terms in Radioecology; Report 77 (2007) provided comprehensive information on Elastic Scattering of Electrons and Positrons; and Report 76 (2006) discussed Measurement Quality Assurance for Ionizing Radiation Dosimetry. Report 80 on Dosimetry Systems for Use in Radiation Processing was published in 2008.
An updated report on Fundamental Quantities and Units is complete and awaiting publication. Reports on Key Data for Measurement Standards in the Dosimetry of Ionizing Radiation and Small-field photon Dosimetry and Applications in Radiotherapy are 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 The Concept of Isoeffective Dose in Radiotherapy 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 committee to report on Measurement and Reporting of Radon Exposures is being formed.
Two reports are being compiled in conjunction with the ICRP and will be published by ICRP: Dose Conversion Coefficients for External Exposures [replacing ICRP Publication 74 and ICRU Report 57 (1998)] and Second Cancers and New Radiation Techniques. Publication of the latter report is expected in 2010.
Future
The responsibility of the 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, and radiation protection. The 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 diagnostic radiology and nuclear medicine, these developments have been rapid, and the 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.
In radiation protection, the ICRU has introduced operational quantities and recommendations for their experimental determination. In basic science, the measurement of physical parameters concerning ionizing radiations 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.
The ICRU is always receptive to suggestions from the scientific and medical communities for new initiatives.
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