IRRADIATION GLOSSARY OF TERMS
TECHNICAL TIP #27
AAMI: Association for the Advancement of Medical
Curie: Radionuclide unit of measure. 1 Curie= 3.7 Becquerel= 1
Instrumentation. Publish guidelines used for sterilization. For
disintegration per second.
irradiation, sterilization documents 11137 and TIR 33 are most
commonly referenced for dose setting. Additional documents
on microbiological testing, materials, etc. related to the device
industry are also available.
Absorbed Dose: Quantity of energy delivered per unit mass of
matter. The unit of absorbed dose is the Gray (Gy). See Kilogray
also.
Accelerated Aging: Storage of product at elevated temperature
and or other intensified conditions (such as humidity) in order to
simulate real time ageing in a shorter period of time.
ANSI: American National Standards Institute
Augmentation: Action taken to increase the sterilization dose
based on the results obtained from a dose audit. Occurs when a
dose audit has failed at the original verification dose.
Bacteriostasis and Fungistasis (B/F): Test performed with
selected microorganisms to demonstrate the presence of
substances that inhibit the multiplication of microorganisms. This
is done prior to a sterility test to assure that the readings of the
sterility test are true. For example, if the product has an inhibitory
effect on bacterial growth, you might get a false sense of security
D10 Value (decimal reduction value): Dose in kGy required to
achieve inactivation of 90% of a population of the test organisms
under stated exposure conditions.
Dose Uniformity Ratio: The ratio of the maximum dose divided
by the minimum dose.
Dosimeter: Device or system having a reproducible, measurable
response to radiation which can be used to measure the
absorbed dose to a product. Common types include Harwell Red
Perspex, alanine pellets, ceric cerous or FWT film.
Dosimetry: Measurement of absorbed dose by the use of
dosimeters
Gamma Ray: Short wavelength, high energy electromagnetic
radiation (photons) emitted from a radioactive material in the
process of nuclear transition. For commercial applications, this is
commonly Cobalt 60.
Half Life: Time required for a radioactive isotope to decay to half
of its original Curie content.
Irradiator: Assembly of equipment that allows safe and reliable
sterilization processing which includes a radiation source,
as to the sterility of the product.
conveyer , carriers or totes, safety devices and shielding, etc.
Bioburden: Population of viable organisms on a product. This
a. Batch irradiator: Irradiator in which containers are introduced
value is used to determine correct verification and sterilization
or removed while the radioactive source is in the storage
dose. This represents the contamination that the product
position.
received in the process of being manufactured. Samples tested
b. Continuous irradiator: Irradiator which can be loaded and
for bioburden are un-irradiated samples from the complete
manufacturing process in final format and packaging.
Cobalt 60: Radioactive isotope of Cobalt 59, produced for
commercial applications by neutron bombardment. Cobalt 59 (27
protons and 32 neutrons) is the stable natural isotope. Cobalt 60
when produced absorbs one additional neutron (27 protons and
33 neutrons). The half life of Cobalt 60 is 5.26 years; the gamma
rays produced as it decays have 1.17 MeV and 1.44 MeV of
emitted energy. These high energy photons can penetrate
deeply into a product, which makes them effective at sterilization.
Colony Forming Unit (cfu): Visible growth of microorganisms
arising from a single cell or multiple cells.
unloaded with product while the source is in the processing
position.
Kilogray: Unit of absorbed dose. 1 Gray (Gy) equals 1 Joule of
energy per Kilogram of product (1 Gray= 100 rads. 1 kilogray is
1000 Joules per Kilogram. This is the mean energy imparted to a
unit of matter divided by the mass of that matter. The kGy is the
international unit of absorbed dose. Older literature may use a
term called Megarad. 1 Megarad equals 10 kGy.
Real Time Aging: Storage of product at ambient conditions in
order to evaluate the function over time.
Recovery Efficiency: Measure of ability of a specific technique
Sterilization Dose: Minimum absorbed dose required to achieve
to remove microorganisms from a product. This is the value that
the specified sterility assurance level.
will be used to give estimated bioburden value that will be used
for dose setting. Common methods for determining recovery
are exhaustive rinse (repeated rinsing of product to recovery
additional organisms) and inoculated recovery (applying known
organisms of a known quantity and trying to recovery them from
product).
SIP (Sample Item Portion): Defined portion of product used for
testing. If entire product is used SIP is 1.0.
Sterile: Free from viable microorganisms. Also see definition of
Verification dose: This is the irradiation dose delivered for
the purpose of doing sterility testing. It represents a Sterility
assurance level of 10-2 (1 in 100) for an AAMI Method 1
validation, or and SAL of 10-1 (1 in 10) for a VDmax25 validation.
These samples, when irradiated are only for testing purposes.
This dose is used to establish and confirm the sterilization dose.
X-ray: Short wavelength electromagnetic radiation emitted by
high energy electrons when they are accelerated, decelerated or
deflected by a strong electric or magnetic field.
sterilization.
Sterility Assurance Level (SAL): Probability of a viable
microorganism being present on a product after sterilization.
Normally expressed as 10-n. Most common SAL for medical
devices is 10-6.
Sterilization: Validated process used to render a product free
from viable microorganisms. The presence of microorganisms is
expressed as a probability. While the probability can be reduced
to a very low number, it can never with certainty be reduced to
zero. This is why we use the term Sterility Assurance level to
express a sterile claim.
For more information, please contact:
STERIS Applied Sterilization Technologies
5960 Heisley Road
Mentor, OH 44077
877.783.7479
www.steris-ast.com
TechTip 27, 05/16, Rev 2