Significance and Use
4.1 Various products and materials are routinely irradiated at pre-determined doses at electron beam facilities to preserve or modify their characteristics. Dosimetry requirements may vary depending on the radiation process and end use of the product. A partial list of processes where dosimetry may be used is given below.
4.1.1 Polymerization of monomers and grafting of monomers onto polymers,
4.1.2 Cross-linking or degradation of polymers,
4.1.3 Curing of composite materials,
4.1.4 Sterilization of health care products,
4.1.5 Disinfection of consumer products,
4.1.6 Food irradiation (parasite and pathogen control, insect disinfestation, and shelf-life extension),
4.1.7 Control of pathogens and toxins in drinking water,
4.1.8 Control of pathogens and toxins in liquid or solid waste,
4.1.9 Modification of characteristics of semiconductor devices,
4.1.10 Color enhancement of gemstones and other materials, and
4.1.11 Research on radiation effects on materials.
4.2 Dosimetry is used as a means of monitoring the irradiation process.
NOTE 2: Dosimetry with measurement traceability and known uncertainty is required for regulated radiation processes such as sterilization of health care products (see ISO 11137-1 and Refs (1-36)) and preservation of food (see ISO 14470 and Ref (4)). It may be less important for other processes, such as polymer modification, which may be evaluated by changes in the physical and chemical properties of the irradiated materials. Nevertheless, routine dosimetry may be used to monitor the reproducibility of the treatment process.
NOTE 3: Measured dose is often characterized as absorbed dose in water. Materials commonly found in single-use disposable medical devices and food are approximately equivalent to water in the absorption of ionizing radiation. Absorbed dose in materials other than water may be determined by applying conversion factors (5, 6).
4.3 An irradiation process usually requires a minimum absorbed dose to achieve the desired effect. There may also be a maximum dose limit that the product can tolerate while still meeting its functional or regulatory specifications. Dosimetry is essential, since it is used to determine both of these limits during the research and development phase, and also to confirm that the product is routinely irradiated within these limits.
4.4 The dose distribution within the product depends on process load characteristics, irradiation conditions, and operating parameters.
4.5 Dosimetry systems must be calibrated with traceability to national or international standards and the measurement uncertainty must be known.
4.6 Before a radiation facility is used, it must be characterized to determine its effectiveness in reproducibly delivering known, controllable doses. This involves testing and calibrating the process equipment, and dosimetry system.
4.7 Before a radiation process is commenced it must be validated. This involves execution of Installation Qualification (IQ), Operational Qualification (OQ), and Performance Qualification (PQ), based on which process parameters are established that will ensure that product is irradiated within specified limits.
4.8 To ensure consistent and reproducible dose delivery in a validated process, routine process control requires that documented procedures are established for activities to be carried out before, during and after irradiation, such as for ensuring consistent product loading configuration and for monitoring of critical operating parameters and routine dosimetry.
Scope
1.1 This practice outlines dosimetric procedures to be followed in installation qualification (IQ), operational qualification (OQ) and performance qualifications (PQ), and routine processing at electron beam facilities.
1.2 The electron beam energy range covered in this practice is between 300 keV and 25 MeV, although there are some discussions for other energies.
1.3 Dosimetry is only one component of a total quality assurance program for adherence to good manufacturing practices used in radiation processing applications. Other measures besides dosimetry may be required for specific applications such as health care product sterilization and food preservation.
1.4 Specific standards exist for the radiation sterilization of health care products and the irradiation of food. For the radiation sterilization of health care products, see ISO 11137-1 (Requirements) and ISO 11137-3 (Guidance on dosimetric aspects). For irradiation of food, see ISO 14470. In those areas covered by these standards, they take precedence. Information about effective or regulatory dose limits for food products is not within the scope of this practice (see ASTM Guides F1355, F1356, F1736, and F1885).
1.5 This document is one of a set of standards that provides recommendations for properly implementing and utilizing dosimetry in radiation processing. It is intended to be read in conjunction with ISO/ASTM 52628, “Practice for Dosimetry in Radiation Processing”.
NOTE 1: For guidance in the calibration of routine dosimetry systems, see ISO/ASTM Practice 51261. For further guidance in the use of specific dosimetry systems, see relevant ISO/ASTM Practices. For discussion of radiation dosimetry for pulsed radiation, see ICRU Report 34.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.