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Significance and Use
4.1 A variety of products and materials may be irradiated with X-radiation to modify their characteristics and improve the economic value or for health-related purposes. Examples are single-use medical devices (sterilization), agricultural commodities (preservation), and various polymeric products (material modification). Dosimetry requirements for X-ray processing may vary depending on the type and end use of the product.
4.2 Dosimeters are used as means of monitoring the radiation process.
NOTE 3 - Dosimetry is required for regulated irradiation processes, such as the sterilization of medical devices and the preservation of food, because the results may affect the health of the consumer. It is less important for other industrial processes, such as polymer modification, which can be evaluated by changes in the physical properties of the irradiated materials. Nevertheless, routine dosimetry may be used to monitor the reproducibility of the treatment process.
NOTE 4 - It is necessary to specify the material in which radiation is absorbed. Frequently, water is selected as the reference material for this purpose. Water is a convenient medium to use because its radiation absorption and scattering properties are close to those of tissue and it is universally available and understood. The requirement of tissueequivalency historically originated from radiation therapy applications. Absorbed dose in materials other than water may be determined by applying conversion factors in accordance with ISO/ASTM Guide 51261.
4.3 Radiation processing specifications usually include a pair of absorbed-dose limits: a minimum value to ensure the intended beneficial effect and a maximum value to avoid product degradation. For a given application, one or both of these values may be prescribed by process specifications or regulations. Knowledge of the dose distribution within irradiated material is essential to meet these requirements.
4.4 Several critical parameters must be controlled to obtain reproducible dose distributions in the processed materials. The processing rate and dose distribution depend on the X-ray intensity, photon energy spectrum, spatial distribution of the radiation field, conveyor speed, and product configuration (see Sections 5, 8, and Annex A1).
4.5 The irradiation process must be qualified to determine its effectiveness in delivering known, controllable doses. This involves testing the process equipment, calibrating the measuring instruments and dosimetry system, and demonstrating the ability of the process to deliver dose distributions in a reliable and reproducible manner (see Sections 9 and 10).
4.6 To ensure consistent dose delivery in a qualified irradiation process, routine process control requires procedures for routine product dosimetry, product handling before and after the treatment, prescribed orientation of the products during irradiation, monitoring of critical process parameters, and documentation of the required activities and functions (see Sections 11 and 12).
1.1 This practice outlines the installation qualification program for an X-ray (bremsstrahlung) irradiator and the dosimetric procedures to be followed during operational qualification, performance qualification and routine processing to ensure that the entire product has been treated within a predetermined range of absorbed dose. Other procedures related to operational qualification, performance qualification and routine processing that may influence absorbed dose in the product are also discussed. Information about effective or regulatory dose limits and energy limits for X-radiation is not within the scope of this practice.
1.2 In contrast to monoenergetic gamma radiation, the bremsstrahlung energy spectrum extends from low values (about 35 keV) up to the maximum energy of the electrons incident on the X-ray target (see Section and ).
1.3 Dosimetry is only one component of a total quality assurance program for an irradiation facility. Other controls besides dosimetry may be required for specific applications, such as medical device sterilization and food preservation.
1.4 For the irradiation of food and the radiation sterilization of health care products, other specific ISO standards exist. 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/ASTM Practice 51431 or ISO 11137, those standards take precedence.Note 1
For guidance in the selection, calibration, and use of specific dosimeters and interpretation of absorbed dose in the product from dose measurements, see the documents listed in Section.Note 2
Bremsstrahlung characteristics are similar to those of gamma radiation from radioactive nuclides. See ISO/ASTM Practices 51204 and 51702 for the applications of dosimetry in the characterization and operation of gamma irradiation facilities. For information concerning electron beam irradiation technology and dosimetry, see ISO/ASTM Practices 51431 and 51649.
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 limitations prior to use.