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BS EN ISO 11137 — Sterilization of Health Care Products — Radiation
Part 1: Requirements for development, validation and routine control of a sterilization process for medical devices; Part 2: Establishing the sterilization dose
☢️ BS EN ISO 11137 specifies requirements for the radiation sterilization of health care products (primarily medical devices), a core standard in the sterile-assurance system for medical devices. The series has two parts: BS EN ISO 11137-1 covers requirements for development, validation and routine control of the sterilization process, and BS EN ISO 11137-2 covers establishing the sterilization dose. Radiation sterilization uses gamma rays, electron beams or X-rays to irradiate the product and inactivate microorganisms; it penetrates well, can sterilise products in their final packaging, and leaves no residue — widely used for single-use medical devices, dressings and pharmaceutical packaging.
💡 The “sterilization dose” is not set arbitrarily: it is derived scientifically from the number (bioburden) and resistance (D₁₀ value) of the product’s initial bioburden using standardised methods (e.g., ISO 11137-2 Method 1/Method 2) to achieve a sterility assurance level (SAL) of 10⁻⁶.
1. Series Overview and Scope 📌
In the UK this series is the responsibility of Technical Committee CH/198 (Sterilization and Associated Equipment and Processes), within ISO/TC 198 “Sterilization of health care products”. BS EN ISO 11137-1:2015 is identical to ISO 11137-1:2006 (including Amd 1:2013), was approved by CEN in June 2015, and supersedes the withdrawn BS EN ISO 11137-1:2006+A1:2013; BS EN ISO 11137-2:2015 is identical to ISO 11137-2:2013, was approved by CEN in June 2015, and supersedes the withdrawn BS EN ISO 11137-2:2013.
| Part | Subject | ICS | ISO Equivalent | Core Content |
|---|---|---|---|---|
| BS EN ISO 11137-1:2015 | Development, validation and routine control | 11.080.01 | ISO 11137-1:2006 (incl. A1:2013) | Requirements and quality management for radiation sterilization processes |
| BS EN ISO 11137-2:2015 | Establishing the sterilization dose | 11.080.01 | ISO 11137-2:2013 | Methods for establishing and verifying the sterilization dose |
⚠️ Radiation sterilization involves ionizing radiation; its facilities, equipment and operation must comply with the relevant radiation-protection regulations and standards. This series specifies the technical requirements of the sterilization process and does not replace ionizing-radiation regulations.
2. Development, Validation and Routine Control (Part 1) 🔧
BS EN ISO 11137-1 specifies requirements for development, qualification and routine control of radiation sterilization processes, including: product families and grouping; facility and equipment qualification (Installation Qualification IQ, Operational Qualification OQ, Performance Qualification PQ); process definition and dose-mapping; use of dosimeters; routine control and release of sterilization batches; revalidation on process change; and records and documentation.
The Standard requires the process to be built on a quality management system and combined with ISO 14971 risk management: through the SAL 10⁻⁶ target, bioburden monitoring, dose audit and microbiological monitoring, each batch achieves the required sterile-assurance level. It also specifies grouping criteria so that a separate process need not be established for each product.
3. Establishing the Sterilization Dose (Part 2) 🔩
BS EN ISO 11137-2 specifies the methods for establishing the sterilization dose. The Standard provides two main methods:
- Method 1: based on the product’s initial bioburden count, deriving the sterilization dose through a specified conversion relationship.
- Method 2: based on experimental determination of the microbial resistance distribution (D₁₀ values) on the product.
After the dose is established, it must be periodically verified by dose audit: testing the bioburden of routine batches to confirm the continued validity of the dose. The Standard gives the specific steps, experimental design, statistical treatment and dose-misuse handling rules for each method.
| Comparison | Method 1 | Method 2 |
|---|---|---|
| Basis | Initial bioburden count | Microbial resistance (D₁₀) testing |
| Experimental effort | Relatively small | Larger (resistance distribution measured) |
| Typical use | Routine products, stable bioburden | Precise dose, highly resistant organisms |
| Verification | Periodic dose audit | Periodic dose audit |
4. Dosimetry and Process Control 🛠️
The core of radiation sterilization process control is dosimetry. The Standard requires the use of calibrated dosimeters to determine the minimum and maximum dose distribution in the load configuration, and specifies the routine minimum-dose measurement requirement for batch release. Dosimeter types include alanine/EPR, calorimetric, and radiochromic film, with uncertainty and calibration frequency per the requirements.
- Dose mapping: determine the dose-extreme positions in the product load.
- Dosimeter audit: verify the actual dose at specified load positions.
- Microbiological monitoring: monitor product bioburden in parallel with the dose audit.
- Change control: re-evaluate on product, packaging or load-configuration change.
5. Engineering Application Practice 🌐
Radiation sterilization is widely used for terminal sterilization of single-use syringes, infusion sets, surgical instruments, dressings, implants and pharmaceutical packaging. Manufacturers (of medical products) and contract sterilizers establish and maintain the process per this series, and regulators assess the product’s sterile-assurance compliance. When choosing radiation sterilization, evaluate the radiation resistance of the product and packaging (degradation, discoloration, performance loss) and make an overall decision considering dose and cost.
🚨 Insufficient dose leads to sterilization failure and contaminated product; excessive dose damages product and packaging. Through sound dose determination, strict dosimetry and periodic audit, ensure each batch is sterilised within the specified dose range and meets the requirement.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between radiation and ethylene oxide (EO) sterilization?
A: Radiation penetrates well, sterilises in final packaging, and leaves no chemical residue, but requires radiation-resistant products; EO is broadly applicable and low-temperature but carries residual-toxicity risk and aeration requirements. Choose per product characteristics and regulation.
A: Radiation penetrates well, sterilises in final packaging, and leaves no chemical residue, but requires radiation-resistant products; EO is broadly applicable and low-temperature but carries residual-toxicity risk and aeration requirements. Choose per product characteristics and regulation.
❓ Q: Why is a dose audit required?
A: The quantity and resistance of the initial bioburden vary with raw materials, process and environment; periodic dose audit confirms the continued validity of the original dose and keeps the SAL consistently met.
A: The quantity and resistance of the initial bioburden vary with raw materials, process and environment; periodic dose audit confirms the continued validity of the original dose and keeps the SAL consistently met.
❓ Q: What does SAL 10⁻⁶ mean?
A: SAL 10⁻⁶ means the probability of a surviving microorganism after sterilization is no greater than 10⁻⁶, i.e., no more than one in a million products may harbour a survivor — the routine target for device sterilization.
A: SAL 10⁻⁶ means the probability of a surviving microorganism after sterilization is no greater than 10⁻⁶, i.e., no more than one in a million products may harbour a survivor — the routine target for device sterilization.
❓ Q: Can all medical devices be radiation-sterilised?
A: Assess the radiation resistance of the product and packaging. Some polymers degrade, discolour or lose performance under irradiation; confirm by test that the product still meets performance and safety requirements after irradiation.
A: Assess the radiation resistance of the product and packaging. Some polymers degrade, discolour or lose performance under irradiation; confirm by test that the product still meets performance and safety requirements after irradiation.