Current status of eye-lens dosimetry in Canada

Abstract

For occupational exposures in planned exposure situations International Commission on Radiological Protection (ICRP) publication 118 recommends an equivalent dose limit for the lens of the eye of 20 mSv yr−1 averaged over five years with no single year exceeding 50 mSv. This constitutes a reduction from the previous limit of 150 mSv yr−1. The Canadian nuclear regulator, the Canadian Nuclear Safety Commission, responded to the ICRP recommendation by initiating amendments to the Radiation Protection Regulations through a discussion paper which was published for comment by interested stakeholders in 2013. The revised equivalent dose limit of 50 mSv in a one-year dosimetry period for nuclear energy workers came into effect in January 2021. This paper presents the outcome of discussions with Canadian stakeholders in diverse fields of radiological work which focused on the implementation of the reduced occupational equivalent dose limit for the lens of the eye in their respective workplaces. These exchanges highlighted the existing practices for monitoring doses to the lens of the eye and identified current technological gaps. The exchanges also identified that, in many cases, the lens of the eye dose is anticipated to be well within the new dose limit despite some of the gaps in technology. The paper also presents the monitoring and eye-lens dose assessment solutions that are available based on different methods for eye-lens monitoring; presented together with criteria for their use.

Electron, Photon, and Neutron Dose Conversion Coefficients of Lens and Non-Lens Tissues Using a Multi-Tissue Eye Model to Assess Risk of Cataracts and Retinitis

“…For whole-body exposures in occupational settings, thermoluminescent and optically stimulated luminescence technologies are typically used to measure dose from X ray, gamma ray, and beta exposures and CR-39 nuclear track detectors are used to measure dose from neutron exposures ( 57 ). With respect to the eye lens dosimetry measurements, Dubeau et al ( 58 ) provides a detailed description of available eye lens dosimeters that seek to measure H p (3), personal dose equivalent delivered to a 3 mm depth in an ICRU cylindrical or slab phantom. H p (3) is an operational quantity that seeks to closely approximate the dose equivalent delivered to the eye lens ( 59 ).…”

“…Commercially available eye lens dosimeters were deemed to provide a satisfactory response to photon radiation, while the response to beta radiation requires improvement ( 60 ). In addition, Dubeau et al ( 58 ) found for neutron eye lens dosimetry, that a selection of commercially available passive neutron dosimeters exists, however their ability to accurately measure neutron eye lens dose has yet to be evaluated. Another study by Dubeau et al ( 61 ) tested the response of five commercially available skin dosimeters each covered by a 300 mg cm –2 thick layer of polycarbonate.…”

On the operational quantity for eye lens neutron dosimetry considering ICRU 95 report

“…As indicated in a recent paper [35], direct monitoring using a dedicated proven H p (3) dosimeter is the preferred method for assessing and ascertaining dose to the lens of the eye. However, in case of unavailability of such a dosimeter, alternative methods may be used when applicable (e.g.…”