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Scope

1.1 This practice covers dosimetric procedures to be followed in Installation Qualification, Operational Qualification and Performance Qualifications (IQ, OQ, PQ), and routine processing at electron beam facilities to ensure that the product has been treated with an acceptable range of absorbed doses. Other procedures related to IQ, OQ, PQ, and routine product processing that may influence absorbed dose in the product are also discussed.

For guidance in the selection and calibration of dosimeters, see ISO/ASTM Guide 51261. For further guidance in the use of specific dosimetry systems, and interpretation of the measured absorbed dose in the product, also see ISO/ASTM Practices 51275, 51276, 51431, 51607, 51631, 51650, and 51956. For use with electron energies above 5 MeV, see Practice E 1026, and ISO/ASTM Practices 51205, 51401, 51538, and 51540 for discussions of specific large volume dosimeters. For discussion of radiation dosimetry for pulsed radiation, see ICRU Report 34.

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 an irradiation facility. Other measures besides dosimetry may be required for specific applications such as medical device sterilization and food preservation.

1.4 Other specific ISO and ASTM standards exist for the irradiation of food and the radiation sterilization of health care products. For food irradiation, see ISO/ASTM Practice 51431. For the radiation sterilization of health care products, see ISO 11137. In those areas covered by ISO 11137, that standard takes precedence.

1.5 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.

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. For example, 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 medical devices,

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,

4.1.11 Research on radiation effects on materials.

NOTE 2 - Dosimetry is required for regulated radiation processes such as sterilization of medical devices (see ISO 11137 and Refs (1-4)5 and preservation of food (see ISO/ASTM 51431 and Ref (5). 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.

4.2 Dosimeters are used as a means of monitoring the radiation process.

NOTE 3 - Measured dose is often characterized as absorbed dose in water to have a traceable standard reference. Moreover, materials commonly found in 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 in accordance with ISO/ASTM Guide 51261.

4.3 A beneficial irradiation process is usually specified by a minimum absorbed dose to achieve the desired effect and a maximum dose limit that the product can tolerate and still be functional. Dosimetry is essential, since it is used to determine these limits, and dosimetry is essential in the evaluation and monitoring of the radiation process.

4.4 The dose distribution within the product depends on process load characteristics, irradiation conditions, and operating parameters. The operating parameters consist of beam characteristics (such as electron energy and beam current), beam dispersion parameters, and product material handling. These critical parameters must be controlled to obtain reproducible results.

4.5 Before a radiation facility is used, it must be qualified to demonstrate its ability to deliver specified, controllable doses in a reproducible manner. This involves testing the process equipment, calibrating the equipment and dosimetry system, and characterizing the magnitude, distribution and reproducibility of the dose absorbed by a reference material.

4.6 To ensure that products are irradiated with reproducible doses, routine process control requires documented product handling procedures before, during and after the irradiation, consistent orientation of the products during irradiation, monitoring of critical process parameters, routine product dosimetry and documentation of the required activities and functions.

Keywords

absorbed dose; dose mapping; dosimeter; dosimetry system; electron beam; ionizing radiation; irradiation; irradiator characterization; radiation; radiation processing ; ICS

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