Radiation Protection Dosimetry (2007), Vol. 124, No. 2, pp. 164–166 Advance Access publication 24 May 2007
doi:10.1093/rpd/ncm203
INDICATORS FOR THE FINGER DOSES IN INTERVENTIONAL RADIOLOGY Erling Stranden1,*, Tonje Seske2, and Anders Widmark2 1 Faculty of Health, Buskerud University College, Konggate 51, Drammen, Norway 2 Norwegian Radiation Protection Authority, Østera˚s, Norway
Received October 20 2006, amended January 4 2007, accepted February 26 2007 Finger doses and other factors have been recorded in order to investigate parameters that could be used to assess the likely level of finger doses of interventional radiologists. A relatively good correlation between finger dose and dose-area product was found regardless of the type of procedure. The correlation between finger dose and screening time was less significant. Very significant correlation between finger doses and the personal dosemeter reading outside the lead apron was found. This strongly suggests that personal dosemeter worn outside the lead apron can serve as a screening device for finger or hand doses to the radiologists. For radiologists, surgeons and cardiologists likely to receive an annual personal dose reading of more than 20 mSv measured outside the lead apron, doses to the hands are likely to be higher than 50 mSv. In these cases, monitoring of finger doses is recommended to establish dose levels.
INTRODUCTION
MATERIALS AND METHODS
There is a potential for staff carrying out interventional procedures in radiology to receive significant radiation doses to their hands(1 – 5). There is a wide range of reported hand doses for interventional radiologists, and there is a potential for annual doses to approach the annual dose limit of 500 mSv given by ICRP(6). This limit also applies in Norway according to national regulations(7). Important factors influencing the dose to the hand are type of procedure, the X-ray equipment used and, not least, the experience and skill of the operator. Routine monitoring of doses to the hands requires a measurement technique which is easy to apply. Furthermore, the use of the monitoring technique should not be a hindrance for the radiologist’s work. It is therefore not a practical approach to monitor the hand or finger doses to all radiologists, but rather apply some screening procedure to define those radiologists whose hand doses are likely to be high. In a study by Whitby and Martin(1), it is suggested that the dose-area product (DAP) could be used as an indicator of the likely dose level, even though the relationship between hand dose and DAP per procedure performed is variable. In the present study, finger doses have been recorded together with other factors for interventional radiological procedures at different hospitals in order to investigate parameters that could be used to assess the likely level of finger doses in order to find individuals or groups that should be monitored especially for finger doses.
Finger doses were recorded by using the thermoluminescence dosemeters (TLDs) DXT_RAD Extremity dosemeters. The dosemeters consist of lithium fluoride doped with magnesium and titanium, LiF:Mg,Ti. The crystal is 0.38-mm thick and mounted on a bar coded disc for identification and placed in a disposable ring during measurement. In the calibrations, the dosemeters were mounted in plastic rings and irradiated on a perspex rod phantom as described in the standard ISO 4037-3(8) with a diameter of 19 mm and a length of 312 mm. The dosemeters used in the X-ray calibrations were calibrated basically in terms of TL-signal related to air kerma free-in-air, using the ion chamber Capintec PM30, traceable to a national standard. The conversion factor hpK(0.07;N)(8) was then used to calculate the equivalent finger dose from the air kerma. More details of reading procedure and calibration are given elsewhere(2). Often, the ring finger or middle finger is used in finger dosimetry. Studies by Whitby and Martin(1), however, conclude that for the radiologist performing a typical mix of interventional procedures, ring dosemeters at the base of the ring finger or little finger will give the best indication of the dose received at the most exposed area. In cardiology the base of the little finger is recommended. During this study, the radiologists therefore were instructed to wear the dosemeters on the base of the little finger bilaterally. Personal dosemeters were also worn by all radiologists participating in the study. The dosemeter was worn at neck position on the outside of lead apron. The dosemeters used were those used in routine
*Corresponding author:
[email protected]
# The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please email:
[email protected]
INDICATORS FOR THE FINGER DOSES IN INTERVENTIONAL RADIOLOGY
Figure 3. Measured finger doses vs. personal dosemeter reading Hp(10).
Figure 1. Measured finger doses vs. DAP.
personal dosimetry supplied by the Norwegian radiation protection authority. The dosemeters are based on LiF TLD crystals supplied by Harshaw. For each dosemeter, two crystals are placed under two different filters representing the ‘shallow dose’, Hp(0.07) and ‘deep dose’, Hp(10). The dosemeters are read on Harshaw model 660 TLD readers. Details on procedure and calibration are given elsewhere(9). In the routine procedure, the dosemeter exposure period is 2 months. In all, 10 radiologists from five hospitals participated in the study. For two of the radiologists, in two different hospitals, the finger doses were recorded for each procedure, while the other radiologists used the standard procedure of 2 months’ exposure time. DAP and screening times were recorded. The DAP values were obtained from the built-in DAP meters of the X-ray machines used
during the procedures. These DAP meters are calibrated by the supplier and are certified to yield correct results within +20%. RESULTS In Figure 1, measured finger doses vs. DAP are given for all our measurements. Data are given for both hands for the individual operators who were followed for 2 months. The data point based on individual procedures is obtained as from the sum of total DAP and dose, respectively, for all the individual procedures. For all the radiologists, the left hand was the most exposed hand as could be expected for right-handed persons. There is a relatively good correlation between DAP and finger dose for the most exposed hand (r ¼ 0.85), whereas the correlation for the other hand is not so good (r ¼ 0.56). In Figure 2, finger dose to the most exposed hand is plotted vs. screening time for single procedures. Here, the correlation is less significant (r ¼ 0.76). In Figure 3, measured finger doses are plotted vs. personal dosemeter readings, Hp(10). Here, the correlation is very good (r ¼ 0.92 and r ¼ 0.87 for most exposed and less exposed hand, respectively). The two lines are given by y ¼ 4.3x and y ¼ 1.6x, respectively. DISCUSSION AND CONCLUSIONS
Figure 2. Measured finger doses vs. screening time for individual procedures.
Even though the total DAP may be used as an indicator, the correlation between DAP and finger dose is not so straightforward. The correlation between finger dose and screening time is even less significant. This was also reported by Sæther et al. (2) These findings are probably explained by the differences in working technique and the choice of exposure parameters.
165
E. STRANDEN ET AL.
The very significant correlation between finger doses and the personal dosemeter reading Hp(10) for a dosemeter worn outside the lead apron supports the assumption that the radiologist who is working closest to the patient for the longest time will receive the highest reading of Hp(10) and, in most cases, the highest finger doses as well. The Norwegian Protection Authority (NRPA) runs an extensive personal dosimetry service(9), but finger doses are not measured to a great extent. In Norway, radiation workers using protective lead aprons are instructed to wear personal dosemeters outside the lead apron at collar height. The results of this work strongly suggest that this dosemeter also can serve as a screening device for finger or hand doses to the radiologists. Even though this study only represents values for radiologists, it could be assumed that this is also the case for surgeons and cardiologists. As seen in Figure 3, the finger dose to the most exposed hand is on average about four times higher than the measured Hp(10). This suggests that for radiologists, surgeons and cardiologists who are likely to receive annual Hp(10) of more than 20 mSv measured on the outside of the lead apron, doses to the hands could exceed 100 mSv and at least are likely to exceed 50 mSv. In these cases, monitoring of finger doses is recommended to establish dose levels. Annually, a small number of cardiologists and radiologists in Norway receive Hp(10) of more than 50 mSv(8) measured on the outside of the lead apron. This indicates that annual doses to their most exposed hand may be in the order of 200– 300 mSv. ACKNOWLEDGEMENTS The authors would like to express their gratitude to the participating interventional radiologists and radiographers at Buskerud Hospital, Haukland University Hospital, Ullevaal University Hospital,
Vestfold Hospital and Tromsoe University Hospital. Valuable inputs from the students A. K. Schanch, E. Storhaug and I. Ellingsen at Buskerud University College are also acknowledged.
REFERENCES 1. Whitby, M. and Martin, C. J. A study of the distribution of dose across the hands of interventional radiologists and cardiologists, Br. J. Radiol. 78, 219 –229 (2005). 2. Sæther, H. K., Davidsen, T.-M., Widmark, A. and Wøhni, T. Measurements of finger doses in x-ray guided surgery, nuclear medicine and research. Rad. Prot. Dosim. 113(4), 392–395 (2005). 3. Cruikshank, J. G., Fraser, G. M. and Law, J. Finger doses received by radiologists during Chiba needle percutaneous cholangiography. Br. J. Radiol. 53, 584– 585 (1980). 4. Vano, E., Gonzales, L., Guibelalde, E., Fernandes, J. M. and Ten, J. I. Radiation exposure to medical staff in interventional and cardiac radiology. Br. J. Radiol. 71, 954– 960 (1998). 5. Vehmas, T. Radiation exposure during standard and complex interventional procedures. Br. J. Radiol. 70, 296– 298 (1997). 6. ICRP. 1990 Recommendations of the International Commission on Radiological Protection. ICRP publication 60. Ann. ICRP 21(1–3) (Oxford: Pergamon Press) (1991). 7. The Norwegian Radiation Protection Authority. Regulations No 1362 of Nov23, 2003 on Radiation Protection and Use of Radiation, http://www.lovdata.no 8. International Organization for Standardization. X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy – Part 3: Calibration of area and personal dosemeters and measurements of their response as a function of energy and angle of incidence. ISO 4037– 3 (Geneva: ISO) (1999). 9. Paulsen, G. U., Sekse, T. and Widmark, A. Annual dose statistics from the Norwegian Radiation Protection Authority, 2004. Stra˚levernRapport 2005: 16, Norwegian Radiation Protection Authority (2005).
166
