Federal/Provincial/Territorial Requirements for Dosimetry Services in Canada

November 20, 2008

Independent Test Specifications for Dosimetry Services: X-Radiation

1. Introduction

Quality in a dosimetry service is defined by accuracy and repeatability of dose measurements. The objective of a quality assurance program in a dosimetry service is to implement a management system that ensures dosimetry results are accurate, repeatable, verifiable, and properly recorded. The quality assurance program in a dosimetry service needs to include the following:

  • Management Policy
  • Quality Assurance Program Description
  • Review by Management
  • Organization and Authority
  • Personnel Qualifications
  • Procurement
  • Work Control
  • Change Control
  • Document Control
  • Calibration and Maintenance
  • Verification
  • Non-conformance
  • Corrective Action
  • Records
  • Independent Audits

Additional details on these can be found in Canadian Nuclear Safety Commission (CNSC) Regulatory Standard S-106 revision 1, Technical and Quality Assurance Requirements for Dosimetry Services dated May 2006.

In addition to the quality assurance program described above, there is a specification for independent testing which must meet the criteria described in Table 1. This is achieved by means of an independent testing program which enables the dosimetry service operator to demonstrate to the appropriate clientele (e.g., employees, customers) and the Provincial Radiation Dosimetry Review Sub-Committee (PRDRSC) that the service's results are reliable.

Table 1: Accuracy Specifications for Dosimeters
Dosimeter Mean Response
R
Coefficient of Variation
Note: For these tests, Table 1 defines the response relative (as defined in S-106 revision 1) to the conventionally true value of the appropriate quantity.
Worn on the torso 0.9 ≤ R ≤ 1.1 ≤ 0.075
Worn on the extremities 0.80 ≤ R ≤ 1.25 ≤ 0.2

The Institute for National Measurement Standards (INMS) of the National Research Council of Canada (NRC) develops, maintains and disseminates primary standards for the measurement of radiation. The INMS may also act directly as the Reference Calibration Centre for the dosimetry of x radiation. In addition, a laboratory using standards directly traceable to the INMS is recognized by the PRDRSC as a reference calibration centre for the dosimetry of x radiation.

Dosimetry services using dosimeters that require processing, e.g., TLDs, must follow the protocol outlined in section 2, below. Dosimetry services using dosimeters, which do not require processing, e.g., electronic dosimeters, must follow the protocol outlined in section 3, below.

2. Protocol for Dosimeters Which Require Processing

2.1 Whole Body Dosimetry

  • (a) At regular intervals and at a frequency of at least annually, or otherwise in consultation with the PRDRSC, each dosimetry service shall send, to a reference calibration centre, at least 50 identified dosimeters per processing unit being tested plus sufficient control dosimeters to satisfy the readout process. For each unit being tested, the reference calibration centre conducting the test will divide the submitted dosimeters into at least 10 groups of at least 5 dosimeters per group. Each group of dosimeters shall be irradiated free-in-air, in an x-ray beam. The x-ray beams used to irradiate the various groups of dosimeters shall be chosen:
    • (i) with different but known exposure (air kerma) between 1.0 mGy (3 x 10-5 C/kg ) and 50 mGy (1.5 x 10-3 C/kg); and
    • (ii) with different but known reference x radiation at 30, 80, 100, 150 and 250 kVcp as defined in the International Standard ISO 4037 Table 2, Narrow Spectrum;
    The delivered exposures (air kerma) for the irradiated dosimeters will not be revealed at this time to the participants but the kVcp used will be indicated.
  • (b) The irradiated dosimeters and controls will be returned to the dosimetry service for processing by the established procedures of the service. The results in exposure (air kerma) units are then reported to the Reference Calibration Centre.
  • (c) The Reference Calibration Centre will compare the reported results with the Reference Calibration Centre values of exposure (air kerma). The results of the independent test (giving both the participant's and the Reference Calibration Centre values) will be reported to the PRDRSC by the Reference Calibration Centre, with a copy to the participant. In order to pass this test, reported results must lie within the criteria described in Table 1.

2.2 Extremity Dosimetry

  • (a) At regular intervals and at a frequency of at least annually, or otherwise in consultation with the PRDRSC, each dosimetry service shall send, to a reference calibration centre, at least 25 identified dosimeters per processing unit being tested plus sufficient control dosimeters to satisfy the readout process. For each unit being tested, the reference calibration centre conducting the test will divide the submitted dosimeters into at least 5 groups of at least 5 dosimeters per group. Each group of dosimeters shall be irradiated free-in-air, in an x-ray beam.

    The x-ray beams used to irradiate the various groups of dosimeters shall be chosen with different but known reference x radiation at 30, 80, 100, 150 and 250 kVcp as defined in the International Standard ISO 4037 Table 2, Narrow Spectrum. Each group of dosimeters shall be irradiated to a different but known exposure (air kerma) between 1.0 mGy (3 x 10-5 C/kg ) and 50 mGy (1.5 x 10-3 C/kg).

    The delivered exposures (air kerma) for the irradiated dosimeters will not be revealed at this time to the participants but the kVcp used will be indicated.
  • (b) The irradiated dosimeters and controls will be returned to the dosimetry service for processing by the established procedures of the service. The results in exposure (air kerma) units are then reported to the Reference Calibration Centre.
  • (c) The Reference Calibration Centre will compare the reported results with the Reference Calibration Centre values of exposure (air kerma). The results of the independent test (giving both the participant's and the Reference Calibration Centre values) will be reported to the PRDRSC by the Reference Calibration Centre, with a copy to the participant. In order to pass this test, reported results must lie within the criteria described in Table 1.

3. Protocol for Dosimeters Which Do Not Require Processing

  • Not to be included at this time.
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