Overview of the Revised Radiation Sterilization Standards (2022)

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Volume 40, Issue 1

1 January 2006

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  • Structure of the Revised Standard

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Research Article| January 01 2006

Eamonn Hoxey

Eamonn Hoxey

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Biomed Instrum Technol (2006) 40 (1): 85–87.

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Eamonn Hoxey; An Overview of the Revised Radiation Sterilization Standards. Biomed Instrum Technol 1 January 2006; 40 (1): 85–87. doi: https://doi.org/10.2345/0899-8205(2006)40[85:AOOTRR]2.0.CO;2

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The current standard for radiation sterilization is ANSI/AAMI/ISO 11137:1994. Work started on preparing this standard in 1990, and it was published in 1995. Under the normal practice of standards organizations, standards are reviewed after five years.

The revision process is now drawing to a close and a revised standard is undergoing its final ballot through the International Organization for Standardization (ISO) and, in the U.S., through AAMI, where it will be adopted as an American National Standard.

Structure of the Revised Standard

This revision was undertaken in parallel with the revision of ANSI/AAMI/ISO standards for industrial ethylene oxide and industrial moist heat sterilization (11135 and 17665, respectively). It was decided that the structure of the standards for the three principle methods of sterilization should be the same.

The revision of ANSI/AAMI/ISO 11137 will be divided into three parts, under the general title ‘Sterilization of health care products—Radiation,’ with each part titled as follows:

  • Part 1—Requirements and guidance;

  • Part 2—Establishing the sterilization dose;

  • Part 3—Guidance on dosimetric aspects.

The main clauses of Part 1 are illustrated in Table 1.

Table 1.

The clauses of ANSI/AAMI/ISO 11137-1 and the aspects covered.

Overview of the Revised Radiation Sterilization Standards (2)

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Overview of the Revised Radiation Sterilization Standards (3)

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(Video) Gamma Irradiation Sterilization Overview | STERIS AST

Check Points

What has changed in ANSI/AAMI/ISO 11137:1994?

✓ Stipulates restrictions on transfer sterilization or verification doses between different electron beam or x-ray irradiators

✓ Balances the frequency of sterilization dose audits with bioburden determinations

Technical Changes

The major technical issues that were addressed in the revision are summarized below.

i) Electron beam energy levels and inclusion of x-rays for sterilization

ISO 11137:1994 set no maximum energy level for electron beams for sterilization or for the generation of x-rays. After considerable discussion among the technical experts, it was agreed that if the energy level of electrons for sterilization exceeds 10 MeV or the energy level for electrons used for the generation of x-rays exceeds 5 MeV, the manufacturer would be required to assess the potential for induced radioactivity in product.

ii) Transferring a sterilization dose

The revised standard stipulates restrictions on transfer of sterilization or verification doses between different electron beam or x-ray irradiators. A manufacturer has to demonstrate that differences in operating conditions of the two irradiators do not alter microbicidal effectiveness unless the transfer is between:

  • two electron sources with identical operating conditions or for doses applied to dry products; and

  • two x-ray radiation sources with identical operating conditions or for doses applied to dry products.

Restrictions also apply to the transfer of sterilization doses determined with gamma radiation to either electron beam or x-ray irradiation.

iii) Dose setting methods

The two methods of dose setting described in Annex B of ISO 11137:1994 have been revised editorially, but there have been no technical changes in the methods themselves.

Users of Method 1 will note that the table listing the verification dose and sterilization dose for a range of levels of average bioburden has been amended so that the table is organized in regular progression of value of average bioburden. Additionally, the lower limit for Method 1 has been set at an average bioburden of 0.1 cfu and the method is not to be applied to average bioburden below this value.

iv) Substantiating a sterilization dose of 25kGy

Method VDmax25 for the substantiation of a sterilization dose of 25 kGy, the basis of which was developed by Kowalski and Tallentire(1 ,2) and published in AAMI TIR27, is included. AAMI TIR27 will be removed from circulation once AAMI/ISO 11137-2 is published.

(Video) TechTalk: Testing & Validation for Radiation Sterilization

v) Dose setting for products with low bioburden

There was considerable discussion among the technical experts regarding methods to determine the sterilization dose for product with a low bioburden.

Manufacturers of products with low bioburden were concerned that they might be penalized by the need to perform extensive microbiological investigation. Therefore, a variation on Method VDmax25, to be designated Method VDmax15 is now included, permitting manufacturers with an average bioburden of less than 1.5 cfu to select and substantiate a sterilization dose of 15kGy.

vi) Maintaining process effectiveness

ISO 11137:1994 contained a requirement for sterilization dose audits to be conducted at three-month intervals. The revised standard recognizes two approaches for specifying the frequency of sterilization dose audits: a time interval of three-months or a time interval based on a documented rationale. This rationale is required to consider: the available data on bioburden and its variation; the controls in place on the manufacturing environment, materials, and processes; and the manner in which the sterilization dose has been established.

The revised standard balances the frequency of sterilization dose audits with that for bioburden determinations; as the sterilization dose audit frequency is reduced, the requirement for routine determinations of bioburden increases. An out-of-specification bioburden result could trigger a sterilization dose audit.

Transition Arrangements

Usual practice on revision of a standard is for the previous version to be withdrawn after six months. This is problematical for a standard used to demonstrate regulatory compliance, as is the case with ANSI/AAMI/ISO 11137:1994. Therefore, a three-year transition period to allow manufacturers adequate time to prepare and revise their supporting processes and documentation has been proposed.

With the expected publication of ANSI/AAMI/ISO 11137-1. −2 and −3 in 2006, this transition period will run until 2009.


The revision of ANSI/AAMI/ISO 11137 will provide manufacturers with opportunities by confirming the international acceptance of Method VDmax25, defining a more flexible approach for maintaining the effectiveness of the sterilization dose, and introducing Method VDmax15 for the substantiation of 15 kGy for the sterilization of product with average bioburden below 1.5 cfu.

AAMI Documents

▪ ANSI/AAMI/ISO 11137:1994Sterilization of health care products - Requirements for validation and routine control - Radiation sterilization. Specifies requirements for validation, process control and routine monitoring in the radiation sterilization of health care products. It applies to continuous and batch type gamma irradiators using the radionuclides 60 Co and 137 Cs, and to irradiators using a beam from an electron or x-ray generator. ST1137 is available in print and PDF. AAMI Member Discount Price: $50. List price: $95. Order code: ST1137. PDF order code: ST1137-PDF.

▪ Medical Equipment Symbols & Safety Signs Clip Art Collection. More than 640 symbols and safety signs for medical equipment are included in this clip art collection from AAMI. Features all of the ISO 15223 and IEC 60878 symbols in several file formats. AAMI Member Discount Price: $ 395. List Price: $495. Order code: SYMBCD.

▪ ANSI/AAMI ST46:2002Steam sterilization and sterility assurance in health care facilities. This recommended practice provides guidelines for steam sterilization in hospitals and other health care facilities. The recommendations are intended to promote assurance of sterility and to guide health care personnel in the proper use of processing equipment. Definitions of terms and a bibliography are also provided. ST46 is available in print and PDF. AAMI Member Discount Price: $50. List price: $95. Order code: ST46. PDF order code: ST46-PDF.

▪ Human Factors Conference CD Package. AAMI is offering a conference CD package, which includes both the PowerPoint slides and audio from each session. Watch the slides, listen to the speakers, and follow the Q&A from the audience. AAMI Member Discount Price: $ 500. List Price: $625. Order code: HFCD.











Substantiation of 25 kGy as a sterilization dose: A rational approach to establishing verification dose.

Radiat. Phys. Chem





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Aspects of putting into practice VDmax.

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Author notes

Dr Eamonn Hoxey is executive director in Europe, the Middle East, and Africa for Johnson & Johnson's Quality & Compliance Worldwide. He is Chairman of CEN TC 204, Sterilization of medical devices, and a member of Working Group 2 of ISO TC 198 on Radiation Sterilization. Dr Hoxey is a Fellow of the Royal Pharmaceutical Society of Great Britain, and is an individual member and past chairman of the Panel on Gamma and Electron Irradiation. Dr Hoxey is a member of the Board of Directors of AAMI.

Overview of the Revised Radiation Sterilization Standards (4)

Copyright: © 2006 This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.


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