staff dosimetry in interventional cardiology: survey ... - Oxford Journals

Radiation Protection Dosimetry (2008), Vol. 129, No. 1–3, pp. 100–103 Advance Access publication 20 February 2008

doi:10.1093/rpd/ncn038

STAFF DOSIMETRY IN INTERVENTIONAL CARDIOLOGY: SURVEY ON METHODS AND LEVEL OF EXPOSURE C. Foti1, *, R. Padovani1, A. Trianni1, C. Bokou2, S. Christofides3, R.H. Corbett4, K. Kepler5, Z. Korenˇova´6, A. Kosunen7, J. Malone8, P. Torbica9, V. Tsapaki10, E. Vano11, J. Vassileva12 and U. Zdesar13 1 Medical Physics Department, Udine Hospital, Italy 2 Luxembourg’s Hospital Association, Luxembourg 3 Medical Physics Department, Nicosia General Hospital, Cyprus 4 Radiology Department,Hairmyres Hospital, UK 5 Tartu University, Estonia 6 Department of Personal Dosimetry, Bratislava, Slovakia 7 STUK, Finland 8 Medical Physics Department, St James’s Hospital, Dublin, UK 9 Department of Radiology, Innsbruck University Hospital, Austria 10 Medical Physics Department, Konstantopoulio Hospital, Athens, Greece 11 Medial Physics Department, S. Carlos University Hospital, Madrid, Spain 12 Laboratory for Radiation Protection in Medicine, Sofia, Bulgaria 13 Institute of Occupational Safety, Slovenia

In interventional cardiac procedures, staff operates near the patient in a non-uniformly scattered radiation field. Consequently, workers may receive, over a period, relatively high radiation doses. The measurement of individual doses to personnel becomes critical due to the use of protective devices and, as a consequence of the large number of methods proposed to assess the effective dose, great variability in monitoring programmes is expected among European countries. SENTINEL consortium has conducted a survey on staff dosimetry methods and on the level of staff exposure in 12 European cardiac centres demonstrating the urgent need to harmonise dosimetry methods. From the dosimetry survey, constraint annual effective dose of 1.4 mSv and Hp(0.07) over the protective apron of 14 mSv are proposed for the optimisation the exposure the most-exposed operator.

INTRODUCTION Cardiac interventional procedures can be complex and involve the extensive use of relatively low dose rate from fluoroscopy and relatively high dose rate from the sequence of image acquisitions. The staff operate near the patient and is exposed to a non-uniform radiation field due to patient-scattered radiation. Consequently, workers may receive, over a period, relatively high radiation doses(1 – 3). According to the European Union Directive 96/ 29/EURATOM, radiation dose to workers has to be expressed in terms of effective dose E (ICRP publication 60)(4), a quantity that is related to the stochastic radiation risk. The avoidance of deterministic effects is instead ensured through limits on equivalent doses H to few specific tissues (extremities, eye lens, skin). Since effective dose, the weighted sum of several organ doses, and equivalent dose cannot be measured in practice, two operational quantities, personal dose equivalents Hp(10) and Hp(0.07), have been defined and recommended by the International Commission on Radiation Units and Measurements *Corresponding author: [email protected]

(ICRU)(5) as conservative estimates of E and Hskin. Thus, effective dose and equivalent dose can in theory be known through readings from dosimeters appropriately located on the body. Both E and Hp(d) vary in a complicated way with radiation type and quality, energy spectrum, fluency rate and X-ray beam direction of incidence. In addition, the use of protective clothing and protective devices makes radiation exposure highly inhomogeneous and assessment of individual dose can result can be problematic. These special situations may then require more than one dosimeter. Recommendations(6 – 9) suggest that if a single dosimeter is used it should be worn outside the apron to monitor doses to skin, eye and unshielded parts of the body even if it will overestimate E. When overestimations are unacceptable, two dosimeters should be used one over and one under the protective apron, as per ICRP Publication 75(7). The interpretation of combined results will have to depend on the local irradiation condition. Consequently, several methods of measurements and algorithms have been proposed to obtain reasonable estimates of the effective dose(10 – 14). A great variety of methods for assessing and different

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REFERENCE LEVELS AT EUROPEAN LEVEL FOR CARDIAC INTERVENTIONAL PROCEDURES

types of monitoring programmes have been expected among European countries and centres. SENTINEL consortium has performed a survey on staff dosimetry methods and on occupational exposure in cardiac interventional rooms among SENTINEL partners. Data arising from these surveys are here reported and discussed.

If only one dosimeter is used under the apron, the effective dose is estimated as Hu/21, as recommended in the NCRP report 122(8).

MATERIALS AND METHODS

Thermoluminescent dosimetry (TLD) is the most widely used technology for personal dosimetry(1 – 3, 10,15 – 17) . In all the investigated centres, TLD is adopted and the TL material mainly used is LiF:Mg. In spite of this uniformity in dosimetry technology adopted, staff dosimetry is performed with different modalities, as emerged from the information collected and reported in Table 1. Only in seven of the investigated centres two personal dosimeters, one under and the other over the apron, as recommended by ICRP, were used for the estimation of the effective dose. In five centres, a single dosimeter was used for the assessment of effective dose: in two of these centres, the dosimeter was worn over the protective apron and in the other three it is worn under the apron. In all centres, cardiologists use a thyroid protection, but these were not always used by nurses and technicians. Furthermore, algorithms employed to estimate E were quite different. The results presented here reflect the fact that deriving effective dose in such non-uniform exposure

A European survey was launched by the SENTINEL consortium to investigate the methods for measuring doses received by the staff employed in interventional cardiac laboratories and the algorithms used for estimating E. For this purpose, a questionnaire was sent in 2005 to more than 20 centres participating in the SENTINEL project. The questionnaire asked for general and technical information about type of personal and area dosimeters, dose quantity measured, dose calculation methods and monitoring programme details. A second questionnaire sent to SENTINEL partners was intended to collect staff exposure data. Radiation dose measurements performed in 12 European countries have been collected. Data were gathered over a period of at least 2 y for two to four cardiologists in each centre. E is calculated using the Niklason algorithm(10) when two measurements, one over apron-collar (Ho) and one under waist (Hu), are available: E ¼ 0:02ðHo  Hu Þ þ Hu

RESULTS Survey on methods for assessing staff doses due to external exposures in interventional cardiology procedures

Table 1. Interventional staff dosimetry survey: dosimetry methods applied in various partner hospitals for cardiologists (Card) nurses and radiographers (Rad). Partner

Number and position of dosimeters Over protective apron

Under protective apron

Algorithm to estimate effective dose Thyroid protection

Card Nurse Rad Card Nurse Rad Card

Nurse

Rad

Ireland Italy

2 1

2 1

— 1

1 1

1 1

1 —

Yes Yes

Yes Yes

Yes Yes

Spain Luxembourg Finland Greece Cyprus Slovak Rep. Estonia Slovenia Bulgaria Scotland

1 1 1 1 1 1 1 — — —

1 — 1 1

1 — 1 1 — 1 — — — —

1 1 — — 1 1 1 1 1 1

1 1 — —

1 1 — — 1 — 1 1 1 1

Yes Yes

Yes Yes

Yes Yes

Yes Yes Yes Yes Yes Yes Yes

Yes Yes No Yes Yes Yes Yes/No

Yes Yes No Yes Yes Yes No

1 — — — —

— 1 1 1 1

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— 1 dos.: E ¼ Hp(10); 2 dos.: E ¼ 0.06[Hp(0.07)2HP(10)]þHP(10) — — Hp(10) E ¼ 0.03Hp(10) (NCRP 22) E ¼ 0.5Hunder þ0.025Hover E ¼ Hp(10)þwskin Hp(0.07) — Hp(10) — Unknown

C. FOTI ET AL. Table 2. Median and third quartile of effective dose and personal dose equivalent over the protective apron for the first operator evaluated in a sample of European cardiac centres. Annual dose (mSv) Effective dose Equivalent dose over the apron (Hover)

Median

Third quartile

1.3 11.1

1.4 14

Occupational doses in interventional cardiac laboratories Staff doses recorded show a large variability: from 0.5 to 6 mSv y21 of effective dose estimated according to the Niklason algorithm. Table 2 summarises the dose distributions from personal dosimeters, providing the median and third quartile, both for the effective dose calculated according to the Niklason algorithm and for the personal equivalent dose measured over the apron, usually at the collar level, of the first and most exposed operator. The latter gives an indication of the level of eye lens exposure. The third quartile values can be adopted as the constraints annual dose for E and Hover, useful to identify poor practices where optimisation action is required. CONCLUSION The SENTINEL survey on staff dosimetry in a sample of European centres has evidenced a large variety of dosimetry methodologies adopted and a wide range of exposure experienced by interventionalists in different centres. This situation requires specific and urgent action aiming to harmonise methods and reduce unnecessary exposure. The SENTINEL consortium thinks the following actions are necessary:

† †

†

to promote the assessment of dose constraints for staff operating in the different interventional area; to promote dosimetry audits aiming to identify poor radiation protection practices.

ACKNOWLEDGEMENT

remains a serious problem since it is not clear which method and which of the many correction factors or algorithms proposed is able to provide the best estimate for E, as recently underlined by Schultz and Zoetelief(18).

†

†

to promote the use of the double dosimetry technique, one over the protective apron at the collar level and the second under the protective apron at the chest or wrist level; to promote studies to identify the most appropriate dosimetry methods and algorithms; to develop a European guideline addressing the staff protection system and dosimetry methods in interventional radiology procedures;

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