below 120 µ.Gy when an undercouch X ray tube and a mechanical contrast injector were used. ..... Entrance dose on the outer surface of the lead apron.
Radiation Protection Dosimetry Vol. 82, No. 2, pp. 93- 103 ( 1999) Nuclear Technology Publishing
DOSIMETRY OF OCCUPATIONALLY EXPOSED PERSONS IN DIAGNOSTIC AND INTERVENTIONAL ARTERIOGRAPHY. PART I: ASSESSMENT OF ENTRANCE DOSES P. J. H. Kicken*, G. J. Kemerink and J. M. A. van Engelshoven Department of Radiology, University Hospital Maastricht P. Debijelaan 25, 6229 HX, Maastricht, The Netherlands
Received October 16 1998, amended December 11 1998, accepted December 14 1998 Abstract- The purpose of this study was to obtain representative quantitative information on exposure conditions and entrance doses of occupationally exposed persons (workers) in diagnostic and interventional arteriography. In a study in three hospitals all parameters of the X ray systems that are related to the exposure of workers were quantified with an automatic data acquisition system. Using LiF thermoluminescence dosemeters, entrance doses to workers were measured at the forehead , neck, thorax , abdomen, upper arms, hands and lower legs. Measurements were performed during 353 procedures, and it was found that exposure of workers was predominantly caused by tluoroscopy. Averaged over all procedures in the annual workload, entrance doses were below 120 µ.G y when an undercouch X ray tube and a mechanical contrast injector were used. For an overcouch tube the doses were higher. It is concluded that entrance doses are low, and that legally established annual dose limits are unlikely to be exceeded.
INTRODUCTION Obtaining quantitative data on radiation dose to occupationally exposed persons is important to demonstrate compliance with dose limits, to assist in quality control and optimisation of radiological procedures, and to provide necessary data for (inter)national organisations that issue recommendations. The foregoing is particularly relevant in the field of diagnostic and interventional endovascular procedures, where relatively high doses to staff are possible. It is, therefore, not surprising that a large number of studies has been performed in this field c1- 11>. The results were in general reassuring, but a few were more alarmingC3 . i 3 .l7). This variance is not only related to the complexity and duration of the procedures involved, but also to differences in radiological methodology. For instance, overcouch X ray tubes and manual contrast injection, two potential sources of high doses to radiological personnel, were still frequently used in published studies. The majority of the investigations assessed entrance doses to tissues at high risk only, and not effective dose (or its precursor effective dose equivalent), although this quantity is certainly of interest for comparison with legally established dose limits and for calculations of collective dose of occupationally exposed workers. Often relatively small numbers of procedures were monitored, and many studies were performed rather long ago for imaging equipment that has probably been improved since then. In the Netherlands a need was felt for new, more representative data. For this reason a study was *Present address: University Hospital Rotterdam, Daniel den Hoed Cancer Center, Groene Hilledijk 301 , 3075 EA Rotterdam, The Netherlands 93
initiated that aimed at quantifying exposure conditions, doses to tissues at risk, and effective dose. To obtain representative data, measurements were performed in three hospitals. The monitored procedures were chosen to cover a significant part of the normal diagnostic and interventional vascular workload (excluding cardiac work). This study was part of a larger project that included assessment of patient dose, the results of which have been published elsewhere 0 8- 20 >. The study into occupational dosimetry will be presented in two parts. Part I (this paper) presents a description of hospitals and procedures monitored, methodology of the measurements, and entrance dose data for exposed persons. Part II comprises new Monte Carlo radiation transport code calculations, effective dose estimates, and relations between effective dose and easily accessible exposure quantities (dose-area product and entrance dose at the neck). MATERIALS AND METHODS
Hospitals and equipment The dose to occupationally exposed persons (workers) was monitored in three hospitals in the south of the Netherlands. These hospitals are referred to as AZM, DW and MA. The AZM is a university hospital, DW and MA are not, but DW like AZM educates radiological residents. Information on the equipment applied for vascular imaging is presented in Table 1. Three modes of imaging were generally used: fluoroscopy, DSA, and serial cut film radiography . In AZM and DW the tube position was usually undercouch, in MA it was initially overcouch, but this was changed to undercouch after the first part of the study had been finished.
P. J. H. KICKEN, G. J. KEMERINK and J. M. A. VAN ENGELSHOVEN
Inherent to the construction of the angiography systems in DW and MA, film exposure in these hospitals was only possible with an overcouch X ray tube. Exposure of workers is related to the exposure of patients, and since this relation is of practical interest, exposure of patients was quantified as well. The X ray system and dose-area product (DAP) meter were electronically interfaced to a PC-based automatic monitoring system. The following data were recorded separately for the three imaging modes ftuoroscopy, DSA and film: dose-area product, tube voltage, X ray diaphragm settings, tube current (ftuoroscopy), tube load (or mA.s value; for radiography and DSA), rotation and angulation, the image intensifier input diameter and the position of the X ray tube along the longitudinal axis of the patient. Fluoroscopy time, the number of DSA frames and the number of films were also recorded automatically. Details of the data acquisition system have been published previously< 21 i.
Assistant: a radiologist, radiologist-trainee or a radiographer, supporting the operator. In MA the assistant was always a radiographer. Ambulant helper: a radiographer, or other medical personnel, providing additional support.
Operators and assistants had to meet sterile working conditions, ambulant helpers had not. Due to the relatively great distance to the patient, and their presence in the protected control room for most of the time, it was anticipated that exposure of ambulant helpers would be low. Therefore, these helpers have not been included in this study. If a radiologist-trainee and a radiologist were involved as operator and assistant, they sometimes switched their activities and positions (AZM and DW). This occurred most frequently if the catheterisation was complicated and required skill and experience not yet mastered by the radiologist-trainee. In the analysis of exposure data a distinction was therefore made between operator, ·assistant and the combined operator/assistant function .
Exposed personnel Protective measures
Workers were classified according to their function: Operator: a radiologist or radiologist-trainee who conducted the medical procedure.
All workers wore protective lead aprons. Characteristics of these aprons are:
Table 1. Features of the angiography X ray systems in the three hospitals. Features of X ray system
Hospitals* DW
AZM
MA
Type
Philips**, Diagnost Arc
Philips, Poly Diagnost UPI
Philips, Poly Diagnost UPI
Generator
Philips, Maximus CM 100 12-pulse generator
Philips, Super Maximus 100 constant voltage
Philips, Optimus M200 constant voltage 2.8 mm Al
Beam filtration
4.5 mm Al
2.8 mm Al
First HVL at 80 kV
3.6 mm Al
2.9 mm Al
2.9 mm Al
Stand
C-shape arm
U-shape arm
U-shape arm
Rotation
-90 to +90°
-90° to 240°
-90° to 240°
Angulation
- 40° to +40°
0° to 35°
0° to 35°
Tube position
Undercouch
Undercouch
Period 1: overcouch Period 2: undercouch
Image intens. (II)
6", HY', 14"
6 11 , 9"
6" 9"
1
Dose rate II (grid)
0.6 µGy .s- at 14"
0.9 µGy .s- 1 at 9"
1.4 µGy .s- 1 at 9"
Dose/DSA frame
Manual setting
9 µGy
9 µGy
X ray focus-II i
26 42 4 II 8 18
20 29 7 43 110 130
51 82 10 100 300 340
88 140 32 180 435 590
17 26 5 34 97 145
-
445 PTA
1220 PTA
2200 PTA
460 PTA
-
4 3 -
18 23 5 37
7 CA2
86
9 22 4 16 39 20
6 II I 9 27 14
79 155 29 165 340 795
23 32 8 36 115 300
245 PTA
115 AAB
91 AAB
3490 CA2
1450 PTA
5.0 7.4 8.4 15 .6 19.3
6.6 9.3
17 5 3
'
