Implications in dosimetry of the implementation of the revised dose limit to the lens of the eye

Report of IRPA task group on issues and actions taken in response to the change in eye lens dose limit

In 2018, the International Radiation Protection Association (IRPA) established its third task group (TG) on the implementation of the eye lens dose limit. To contribute to sharing experience and raising awareness within the radiation protection community about protection of workers in exposure of the lens of the eye, the TG conducted a questionnaire survey and analysed the responses. This paper provides an overview of the results of the questionnaire.

Monitoring neurointerventional radiation doses using dose-tracking software: implications for the establishment of local diagnostic reference levels

OBJECTIVES

There is potential for high radiation exposure during neurointerventional procedures. Increasing regulatory requirements mandate dose monitoring of patients and staff, and justification of high levels of radiation exposure. This paper demonstrates the potential to use radiation dose-tracking software to establish local diagnostic reference levels.

METHODS

Consecutive neurointerventional procedures, performed in a single institution within a one-year period, were retrospectively studied. Dose area product (DAP) data were collected using dose-tracking software and clinical data obtained from a prospectively generated patient treatment database.

RESULTS

Two hundred and sixty-four procedures met the selection criteria. Median DAP was 100 Gy.cm² for aneurysm coiling procedures, 259 Gy.cm² for arteriovenous malformation (AVM) embolisation procedures, 87 Gy.cm² for stroke thrombolysis/thrombectomy, and 74 Gy.cm² for four-vessel angiography. One hundred and nine aneurysm coiling procedures were further studied. Six significant variables were assessed using stepwise regression analysis to determine effect on DAP. Aneurysm location (anterior vs posterior circulation) had the single biggest effect (p = 0.004).

CONCLUSIONS

This paper confirms variable radiation exposures during neurointerventional procedures. The 75th percentile (used to define diagnostic reference levels) of DAP measurements represents a reasonable guidance metric for monitoring purposes. Results indicate that aneurysm location has the greatest impact on dose during coiling procedures and that anterior and posterior circulation coiling procedures should have separate diagnostic reference levels.

KEY POINTS

• Dose-tracking software is useful for monitoring patient radiation dose during neurointerventional procedures • This paper provides a template for methodology applicable to any interventional suite • Local diagnostic reference levels were defined by using the 75th percentile of DAP as per International Commission on Radiological Protection recommendations • Aneurysm location is the biggest determinant of radiation dose during coiling procedures. • Anterior and posterior circulation coiling procedures should have separate diagnostic reference levels.

EYE LENS DOSIMETRY WITHIN THE CARDIAC CATHETERISATION LABORATORY-ARE ANCILLARY STAFF BEING FORGOTTEN?

Eye lens doses have been widely explored for interventional clinicians, however, data for ancillary staff is limited. Eye doses have been measured using a headband technique for clinicians, specialist registrars, nurses and radiographers working in a cardiac catheterisation laboratory in a UK hospital. Workload was found to be significantly higher for ancillary staff, and consequently, despite the absolute monthly collar doses and other indicators such as eye dose/KAP and eye dose/procedure being highest for clinicians, our study found there was no significant difference in the monthly eye dose readings between the clinicians and nurses (p = 0.82), and clinicians and radiographers (p = 0.72). The average eye dose/collar dose ratios were 0.71 and 0.61 for cardiologists and SPRs, but ratios above one were found for nurses and radiographers. This work expands on the eye dose data available for ancillary staff and demonstrates that eye dosimetry for these workers should not be overlooked.

Report of IRPA task group on the impact of the eye lens dose limits

In 2012 IRPA established a task group (TG) to identify key issues in the implementation of the revised eye lens dose limit. The TG reported its conclusions in 2013. In January 2015, IRPA asked the TG to review progress with the implementation of the recommendations from the early report and to collate current practitioner experience. This report presents the results of a survey on the view of the IRPA professionals on the new limit to the lens of the eye and on the wider issue of tissue reactions. Recommendations derived from the survey are presented. This report was approved by IRPA Executive Council on 31 January 2017.

ON-FIELD EVALUATION OF OPERATOR LENS PROTECTIVE DEVICES IN INTERVENTIONAL RADIOLOGY

The recent publication of the Euratom Directive 2013/59, adopting the reduction of eye lens dose limits from 150 to 20 mSv y^-1, calls for the development of new tools and methodologies for evaluating the eye lens dose absorbed by the medical staff involved in interventional radiology practices. Moreover, the effectiveness of the protective devices, like leaded glasses, which can be employed for radiation protection purposes, must be tested under typical exposure scenarios. In this work, eye lens dose measurements were carried out on an anthropomorphic phantom simulating a physician bound to perform standard interventional neuroradiology angiographic procedures. The correlation between eye lens doses, in terms of Hp(0.07), and the equivalent dose [again in terms of Hp(0.07)] monthly measured with thermoluminescent dosemeters placed above the lead apron at the chest level was studied, in the presence and in the absence of different types of leaded glasses.

Eye lens monitoring for interventional radiology personnel: dosemeters, calibration and practical aspects of H p (3) monitoring. A 2015 review

A thorough literature review about the current situation on the implementation of eye lens monitoring has been performed in order to provide recommendations regarding dosemeter types, calibration procedures and practical aspects of eye lens monitoring for interventional radiology personnel. Most relevant data and recommendations from about 100 papers have been analysed and classified in the following topics: challenges of today in eye lens monitoring; conversion coefficients, phantoms and calibration procedures for eye lens dose evaluation; correction factors and dosemeters for eye lens dose measurements; dosemeter position and influence of protective devices. The major findings of the review can be summarised as follows: the recommended operational quantity for the eye lens monitoring is H p (3). At present, several dosemeters are available for eye lens monitoring and calibration procedures are being developed. However, in practice, very often, alternative methods are used to assess the dose to the eye lens. A summary of correction factors found in the literature for the assessment of the eye lens dose is provided. These factors can give an estimation of the eye lens dose when alternative methods, such as the use of a whole body dosemeter, are used. A wide range of values is found, thus indicating the large uncertainty associated with these simplified methods. Reduction factors from most common protective devices obtained experimentally and using Monte Carlo calculations are presented. The paper concludes that the use of a dosemeter placed at collar level outside the lead apron can provide a useful first estimate of the eye lens exposure. However, for workplaces with estimated annual equivalent dose to the eye lens close to the dose limit, specific eye lens monitoring should be performed. Finally, training of the involved medical staff on the risks of ionising radiation for the eye lens and on the correct use of protective systems is strongly recommended.