Radiation Protection Dosimetry (2015), Vol. 163, No. 2, pp. 181 –187 Advance Access publication 3 May 2014
doi:10.1093/rpd/ncu148
INFLUENCE OF STANDING POSITIONS AND BEAM PROJECTIONS ON EFFECTIVE DOSE AND EYE LENS DOSE OF ANAESTHETISTS IN INTERVENTIONAL PROCEDURES Y. Kong1, L. Struelens2, F. Vanhavere2, C. S. Vargas2, W. Schoonjans2 and W. H. Zhuo1, * 1 Institute of Radiation Medicine, Fudan University, Xietu Road 2094, Shanghai 200032, China 2 Radiation Protection Dosimetry and Calibration, Belgian Nuclear Research Centre, SCK.CEN, Boeretang 200, Mol 2400, Belgium
Received 27 January 2014; revised 2 April 2014; accepted 4 April 2014 More and more anaesthetists are getting involved in interventional radiology procedures and so it is important to know the radiation dose and to optimise protection for anaesthetists. In this study, based on Monte Carlo simulations and field measurements, both the whole-body doses and eye lens dose of anaesthetists were studied. The results showed that the radiation exposure to anaesthetists not only depends on their workload, but also largely varies with their standing positions and beam projections during interventional procedures. The simulation results showed that the effective dose to anaesthetists may vary with their standing positions and beam projections to more than a factor of 10, and the eye lens dose may vary with the standing positions and beam projections to more than a factor of 200. In general, a close position to the bed and the left lateral (LLAT) beam projection will bring a high exposure to anaesthetists. Good correlations between the eye lens dose and the doses at the neck, chest and waist over the apron were observed from the field measurements. The results indicate that adequate arrangements of anaesthesia device or other monitoring equipment in the fluoroscopy rooms are useful measures to reduce the radiation exposure to anaesthetists, and anaesthetists should be aware that they will receive the highest doses under left lateral beam projection.
INTRODUCTION During X-ray guided interventional radiology procedures, medical staff are exposed to high radiation dose since they work in a fluoroscopy room with large amount of scattered radiation. The primary operators who usually stay longer and stand closer to the patient’s right side are most likely to receive the highest exposure among all staff involved in interventional procedures. The radiation exposure to the primary operator has been widely investigated and measures of radiation protection were also recommended(1 – 4). With the rapid popularisation and development of new techniques in interventional radiology, more and more anaesthetists who operate the anaesthesia device and check other monitoring equipment are involved in the clinical procedures for the patient care. During interventional procedures, the anaesthetists usually stay shorter time in the fluoroscopy room than the primary operators. It was thought that their radiation exposure would be lower than the primary operators. However, recent surveys indicated that their exposure could also be relatively high. Anastasian et al. (5) found that the averaged radiation exposure to anaesthetists’ face was .3-fold of the exposure to radiologists in the neurointerventional suite. Ismail et al. (6) reported that the averaged dose to anaesthetists was 0.28 mSv for an endoscopic retrograde cholangiopancreatography procedure and 2.32 mSv in cardiac catheterisation
suite over 6 months. Routine monitoring of radiation for anaesthetists working in the cardiac catheterisation laboratory was also suggested by Henderson et al.(7). Compared with the primary operators, the anaesthetists usually stand on the left side or the head side of the patients, and their standing positions are more flexible. It is thought that their exposure can be reduced by changing their standing positions and trying to avoid the main scattered radiation according to the X-ray beam projections. In this work, based on Monte Carlo simulations, both the effective dose and eye lens dose of anaesthetists were calculated under different irradiation conditions. The effect of four standing positions of anaesthetists and some common beam projections on the effective dose and eye lens dose were studied and partially compared with field measurements. Furthermore, the correlations between the eye lens dose and personal dose equivalent HP(10) over apron were also estimated.
MATERIALS AND METHODS Simulations For Monte Carlo simulations, the software MCNPX version 2.5.0 was used(8). Similar scenarios, which were observed during the field measurements of this study for anaesthetists were simulated in the Monte Carlo set-up. A modified ORNL-MIRD phantom(6, 9)
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Western Ontario on June 9, 2015
*Corresponding author: [email protected]
Y. KONG ET AL.
The number of simulated source photons was set to be 108 for all simulations. Assuming the organ factors including size and density to be constant, the uncertainty of the effective dose or HP(3) was propagated from the uncertainty of calculated organs/tissue doses. The uncertainty of effective dose was ,5 %, and the uncertainty HP(3) was generally ,10 %. Measurements Field measurements were carried out for 12 neurology (INR), 10 radiofrequency ablation (RFA) and 9 vertebroplasty interventional procedures in two Belgian hospitals. Information including the standing positions of anaesthetists, total KAP, exposure time and shielding facilities was also recorded during the measurements. For each procedure, the eye lens dose of anaesthetists TM was measured by the Eye-D dosemeter(11) which was calibrated against HP(3). This dosemeter is composed of an MCP-N (LiF:Mg,Cu,P) type of thermoluminescent detector (TLD) and an optimised polyamide capsule. The lower limit of detection (LLD) for the dosemeter was estimated as twice its background variation (2sBG). Four chips of the TLDs were kept in the laboratory as background control. If the readout value of the TLD was lower than the LLD, the value was recorded as half of the LLD value(12). For each procedure, four DIS-1 dosemeters(13) were used to monitor the personal dose equivalent HP(10) at the level of the neck over the thyroid collar, the waist over the apron and the chest level over and under the apron. DIS dosemeters were positioned on the side facing the X-ray tube. Therefore, in cases where the anaesthetist turned away from the X-ray tube, the DIS was positioned on his back. The effective dose was estimated with different single and double-dosimetry algorithms for interventional radiology personnel, with the HP(10) measured at the neck over the thyroid collar and chest level under the apron. These results are also compared with the calculated effective doses. Additionally, correlations between eye lens dose and HP(10) values over apron at those three sites were also explored, respectively. The DIS detector was tested within the ORAMED project in a scattered radiation field, and its overall uncertainty was 20 % (2s)(14). For TLDs, a 20 % (2s) measurement uncertainty was also considered(15). RESULTS AND DISCUSSION Calculated effective dose
Figure 1. Four main standing positions of anaesthetists in interventional procedures.
The normalised effective dose (E/KAP) of an anaesthetist in different conditions of standing positions and beam projections were calculated and are shown in Figure 3. As shown in Figure 3, the normalised effective doses depend not only on the standing
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was used as a patient and the reference male voxel phantom(10) was used to represent an anaesthetist. In all simulations, the anaesthetist wears a 0.5-mm Pb lead apron, which fits well to the body with a thyroid shield. An X-ray spectrum corresponding to a tube voltage of 80 kVp with a filtration of 3 mm Al was used. The X-ray photons were supposed to emit from a point source and collimated into a cone with a field diameter at the entrance of the image intensifier of 40 cm and the distance from source to detector was fixed to 90 cm. The image intensifier was simplified to be a radiation absorber and the thickness of the window was set to be 1.5 mm Al. The four mostly observed standing positions of anaesthetists in the field measurements of this study are illustrated in Figure 1 and the X-ray beam projections are illustrated in Figure 2. For the head irradiation, seven X-ray beam projections were considered, namely as posterio-anterior (PA), right anterior oblique (458RAO), left lateral (LLAT), right lateral (RLAT), left anterior oblique (458LAO), caudal (308CAUD) and cranial (308CRAN). For the thorax irradiation, five projections were considered, i.e. PA, 458RAO, 458LAO, LLAT and RLAT. The energy deposition in different organs or tissues was calculated by using F6 tally in the MCNP code in the voxel model representing anaesthetists. Based on the calculated organ doses and the tissue weighting factors recommended in ICRP 103, the effective dose was summed up over the equivalent doses for all organs and tissues. Eye lens dose was calculated in a small volume of 3-mm depth at the eye positions to represent HP(3). As the simulation results of MCNPX were normalised by the number of simulated particles in order to compare the results with the measured quantity, the calculated doses were further normalised to the kerma area product (KAP) in this work. Therefore, along the beam axis, a thin air layer between the X-ray focal spot and patient was constructed to simulate the KAP value, which is the product of the air kerma to the layer and the area of the X-ray beam on the layer.
ANAESTHETIST DOSE IN INTERVENTIONAL PROCEDURES
Figure 3. Effective dose of anaesthetists calculated under different conditions: (a) head irradiation and (b) thorax irradiation.
positions, but also on the beam directions. For the head irradiation, the highest dose of 0.096 mSv (Gy21 cm22) at the P-2 position under LLAT projection is 12 times higher than the lowest of 0.007 mSv (Gy21 cm22) at the P-4 position under 458LAO. While for the thorax irradiation, the highest of 0.156 mSv (Gy21 cm22) at the P-3 position under LLAT projection is 13 times higher than the lowest of 0.011 mSv (Gy21 cm22) at the P-4 position under 458LAO. For the head irradiation, the effective doses at P-1, P-2, P-3 and P-4 were averaged to be 0.059, 0.046, 0.035 and 0.016 mSv (Gy21 cm22) for the seven different beam projections, respectively. For the thorax irradiation, the doses at P-1, P-2, P-3 and P-4 were averaged to be 0.037, 0.042, 0.059 and 0.033 mSv (Gy21 cm22) for the five different beam projections, respectively. The results are reasonable because P-1 for the head irradiation and P-3 for the thorax irradiation are closer to the centre of radiation fields than the position of P-4. Therefore, in order to reduce the radiation exposure to anaesthetists, it is suggested to set the anaesthesia device and other monitoring equipment as far away from the bed as possible
provided the changes of positions do not affect the patient care during the interventional procedures. Furthermore, it is found that the doses to anaesthetists at the same position are always the highest under LLAT projections among the different beam projections. It suggests that the anaesthetists should avoid staying at their positions when the beam is on with the LLAT projection. However, from the viewpoint of radiation exposure, the LLAT projection is generally preferable for primary operators(5, 16). Therefore, under the instructions of primary operators, a selection of a reasonable time to enter the fluoroscopy room can also reduce the radiation exposure to anaesthetists. Calculated eye lens dose The normalised eye lens dose (HP(3)/KAP) of an anaesthetist in different conditions of standing positions and beam projections were calculated and are shown in Figure 4. As shown in Figure 4, the normalised eye lens doses depend on not only the standing positions, but also on the beam directions. For the head
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Figure 2. Simulated X-ray beam projections in head or thorax irradiation.
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Table1. Comparisons among effective doses derived from different algorithms for 12 INR procedures. Algorithma
Positions of dosemeters Single dosimetry Huyskens et al. (1994 )(17) (18)
McEwan (2000)
Double dosimetry Wambersie et al. (1993)(19) (18)
McEwan (2000)
Clerinx et al. (2008)(20) von Boetticher (2010) a
Effective doseb (mSv (Gy21 cm22))
Hu: trunk under apron Ho: trunk over apron Hu: trunk under apron Ho: collar over shield
E ¼ 3 Hu E ¼ 0.2 Ho E ¼ 2 Hu E ¼ 0.08 Ho
0.046 (0– 0.097) 0.049 (0.003– 0.121) 0.031 ( 0 –0.065) 0.009 (0.001– 0.032)
Hu: chest under apron Ho: neck/shoulder over shield Hu: trunk under apron Ho: collar over shield Hu: chest under apron Ho: neck over shield Hu: chest under apron Ho: neck over shield
E ¼ Hu þ 0.1Ho
0.027 (0.003– 0.057)
E ¼ 0.71Hu þ 0.05Ho
0.017 (0.001– 0.035)
E ¼ 1.64Hu þ 0.075Ho
0.034 (0.002– 0.070)
E ¼ 0.84Hu þ 0.051Ho
0.019 (0.001– 0.039)
Hu and Ho represent HP(10) under or over apron/thyroid shield. Dose value is exhibited as mean (min –max).
b
irradiation, the highest dose of 2.228 mSv (Gy21 cm22) at P-1 under RLAT projection is .500 times higher than the lowest of 0.004 mSv (Gy21 cm22) at P-2 under 458LAO. While for thorax irradiation, the highest dose of 2.399 mSv (Gy21 cm22) at P-1 under RLAT projection is nearly 200 times of the lowest of 0.012 mSv (Gy21 cm22) at P-2 under 458LAO. Under different beam projections, the averaged eye lens doses are 1.305, 0.278, 0.555 and 0.281 mSv (Gy21 cm22) at P-1, P-2, P-3 and P-4 for the head irradiation, and 1.209, 0.321, 0.955 and 0.522 mSv (Gy21 cm22) for the thorax irradiation, respectively. The dose at P-1 presents the highest dose among the four positions. It suggests that the anaesthetists should avoid staying at P-1 during the interventional procedures and facing to the patients. Furthermore, it is also found that the eye lens doses of anaesthetists are generally much higher under LLAT or RLAT projections than under other beam projections. It also suggests that the anaesthetists
should avoid staying at their positions when the beam is on with the LLAT or RLAT projections. Comparisons By applying the algorithms for the estimation of the effective dose suggested by other researches, the effective doses for anaesthetists during INR procedures were calculated and is shown in Table 1. As listed in Table 1, compared with single dosimetry (SD), more narrow ranges of effective dose values are found with the double dosimetry (DD). It implies that the DD will give a more stable result, while the SD is more likely to lead to a larger deviation. For the averaged dose, different algorithms lead to a maximal difference by a factor of over 5. As these algorithms were suggested for main operators during interventional procedures, further studies are still needed to provide a more accurate algorithm to estimate the effective dose of anaesthetists.
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Figure 4. Eye lens dose of anaesthetists calculated under different conditions: (a) head irradiation and (b) thorax irradiation.
ANAESTHETIST DOSE IN INTERVENTIONAL PROCEDURES Table 2. Comparisons between the simulated and measured dosea.
Measurement INR (head) Vertebroplasty (thorax) RFA (thorax) Simulation INR (head) Vertebroplasty (thorax) RFA (thorax)
No.
Positions
Effective dose, mean (range)
Eye lens dose, mean (range)
12 9 10
P-2, P-3, P-4 P-2, P-3 P-1
0.019 (0.001– 0.039) 0.071 (0– 0.159) 0.092 (0– 0.268)
0.384 (0.093– 1.353) 0.592 (0.144– 1.337) 2.208 (0.504– 5.422)
P-2, P-3, P-4 P-2, P-3 P-1
0.032 (0.007– 0.096) 0.050 (0.013– 0.156) 0.037 (0.024– 0.056)
0.371 (0.004– 1.287) 0.638 (0.012– 2.246) 1.209 (0.536– 2.399)
a
During this study, both the effective dose and eye lens dose for .30 anaesthetists were monitored. For easy comparisons, both the simulated and measured doses were normalised to the KAP first, and then the comparison result is listed in Table 2. As seen from Table 2, simulated doses are in a reasonable range compared with measured ones. The variances may arise from the different dimensions between the standard voxel phantom and the anaesthetists. Moreover, the exact position and movement of the anaesthetist are also hard to be accurately simulated. As shown in Table 2, the normalised dose in average differs from the procedure types, with the highest for the RFA procedure. Moreover, even for the same type of procedure, the dose also obviously varies among different measurements. Anaesthetists were not always in the fluoroscopy room, they entered the room only when needed during the procedure. Besides the total exposure time for anaesthetists were different, the beam projections were not necessary the same when they entered the rooms. However, the authors still have a strong impression that if the anaesthetist stayed significantly longer, their doses are higher. The eye lens dose of the anaesthetists was averaged to be 68 mSv per INR procedure in this study. It was 10 times higher the value (6.5 + 5.4 mSv) in similar quantity (exposure to the face) reported by Anastasian et al. (5). In Anastasian’s study, there was a shield between the anaesthetist and fluoroscopy equipment, while there was not any protection shield for the anaesthetists in this work. It indicates that an additional shield set between the anaesthetist and fluoroscopy equipment may significantly reduce the eye lens dose of anaesthetists. Correlation between the eye lens dose and HP(10) measured at other points Figure 5 shows the results of the eye lens dose HP(3) and HP(10) over apron at neck, chest and waist level measured for the 30 anaesthetists in this work. Fitted
by the least squares method by using the software Origin 9.0, fairly good correlations between the HP(3) and HP(10) at neck, chest or waist could be observed. Recently, through a simulated anthropomorphic study, Farah et al.(21) has also reported that the HP(3) correlates best with HP(10) at left collar level for main operators. It indicates that the eye lens dose of the anaesthetists can also be estimated by other monitoring results usually performed. Based on the measurement results and an assumed annual workload of 200 procedures for an anaesthetist, the annual averages of the effective dose and eye lens dose were estimated to be 0.44 mSv and 8.8 mSv, respectively. The effective dose was much smaller than the value reported by Ismail et al.(6). The main reason was thought that the algorithm used here to estimate the dose to anaesthetists was different. However, the eye lens dose was still relatively high. It indicates that more attention should be paid to protect the eye lens even though the effective dose is not so high. CONCLUSION In this study, based on Monte Carlo simulations and field measurements, both the effective dose and eye lens dose of anaesthetists in some interventional procedures were studied. The results showed that the radiation exposure to anaesthetists depends not only on their standing positions, but also on the beam projections used during interventional procedures. In general, a close position to the bed and the left lateral (LLAT) beam projection will deliver a higher exposure to anaesthetists. The eye lens dose of an anaesthetist may reach several tens of microSieverts in a single procedure. Reducing stay time in the fluoroscopy room, enlarging distance and radiation shield can reduce their radiation dose. Adequate arrangements of anaesthesia device or other monitoring equipment in the fluoroscopy rooms are useful measures to reduce the radiation exposure to anaesthetists. Anaesthetists should be aware to avoid to enter the
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The unit of dose is in mSv (Gy21 cm22). Measured effective doses were estimated based on von Boetticher’s algorithm (2010). The simulated doses were summarised over seven and five beam projections for head and thorax irradiation, respectively.
Y. KONG ET AL.
further research works are still needed to study the effects of different thicknesses of the lead apron and the X-ray filtration, different postures of the anaesthetist at work, and so on.
FUNDING The work was partially supported by the National Natural Science Foundation of China (grant no. 11075040).
Figure 5. Correlation between the eye lens dose HP(3) and HP(10) at neck, chest and waist over aprons.
room when the X-ray beam is on under the LLAT beam projection. The eye lens dose of anaesthetists can be roughly estimated from the doses measured at the neck, chest or waist by using routinely used personal dosemeters. For more accurate estimations of the radiation exposure to anaesthetists in the interventional procedures,
1. Van˜o´, E., Gonza´lez, L., Guibelalde, E., Ferna´ndez, J. M. and Ten, J. I. Radiation exposure to medical staff in interventional and cardiac radiology. Br. J. Radiol. 71, 954– 960 (1998). 2. Ja¨rvinen, H., Buls, N., Clerinx, P., Jansen, J., Miljanic´, S., Nikodemova´, D., Ranogajec-Komor, M. and D’Errico, F. Overview of double dosimetry procedures for the determination of the effective dose to the interventional radiology staff. Radiat. Prot. Dosim. 129(1– 3), 333– 339 (2008). 3. Carinou, E. et al. Recommendations to reduce extremity and eye lens doses in interventional radiology and cardiology. Radiat. Meas. 46, 1324–1329 (2011). 4. Kong, Y., Gao, L., Zhuo, W. and Qian, A. A survey on radiation exposure of primary operators from interventional X-ray procedures. Radiat. Meas. 55, 43– 45 (2013). 5. Anastasian, Z. H., Strozyk, D., Meyers, P. M., Wang, S. A. and Berman, M. F. Radiation exposure of the anesthesiologist in the neurointerventional suite. Anesthesiology 114, 512–520 (2011). 6. Ismail, S., Khan, F., Sultan, N. and Naqvi, M. Radiation exposure to anaesthetists during interventional radiology. Anaesthesia 65, 54–60 (2010). 7. Henderson, K. H., Lu, J. K., Strauss, K. J., Treves, S. T. and Rockoff, M. A. Radiation exposure of anesthesiologists. J. Clin. Anesth. 6, 37–41 (1994). 8. Pelowitz, D. B. MCNPX User’s Manual, Version 2.5.0. Report LA-CP-05e0369. Los Alamos National Laboratory (2005) 9. Snyder, W. S., Ford, M. R. and Warner, G. G. Estimates of absorbed fraction for monoenergetic photon sources uniformly distributed in various organs of a heterogeneous phantom. Report ORNL-4979. Oak Ridge National Laboratory (1978). 10. ICRP. Adult Reference Computational Phantoms. ICRP Pub. 110. Ann. ICRP 39 (Oxford: Elsevier) (2009). 11. Bilski, P. et al. The new EYE-DTM dosemeter for measurements of HP(3) for medical staff. Radiat. Meas. 46, 1239–1242 (2011). 12. The Ministry of Health of the People’s Republic of China. Specifications of Individual Monitoring for Occupational External Exposure (GBZ128– 2002). (Beijing: China Standards Press) (2002). 13. Kahilainen, J. The direct ion storage dosemeter. Radiat. Prot. Dosim. 66(1– 4), 459–462 (1996). 14. Struelens, L., Carinou, E., Clairand, I. et al. Use of active personal dosemeters in interventional radiology and
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REFERENCES
ANAESTHETIST DOSE IN INTERVENTIONAL PROCEDURES 18. McEwan, A. C. Assessment of occupational exposure in New Zealand from personal monitoring records. Radiat. Prot. Australas. 17, 60– 66 (2000). 19. Wambersie, A. and Delhove, J. Radiation protection in diagnostic radiology, a debated practice: how to wear the individual dosemeters? J. Belg. Radiol. 76, 382–385 (1993). 20. Clerinx,, P., Buls, N., Bosmans, H. and de Mey, J. Doubledosimetry algorithm for workers in interventional radiology. Radiat. Prot. Dosim. 129(1–3), 321–327 (2008). 21. Farah, J., Struelens, L., Dabin, J., Koukorava, C., Donadille, L., Jacob, S., Schnelzer, M., Auvinen, A., Vanhavere, F. and Clairand, I. A correlation study of eye lens dose and personal dose equivalent for interventional cardiologists. Radiat. Prot. Dosim. 157(4), 561–569 (2013).
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cardiology: tests in hospitals—ORAMED project. Radiat. Meas. 46, 1258– 1261 (2011). 15. Vanhavere, F. et al. ORAMED: optimization of radiation protection of medical staff. EURADOS Report 2012-02 (2012). ISSN 2226-8057. 16. Koukorava, C., Carinou, E., Simantirakis, G., Vrachliotis, T. G., Archontakis, E., Tierris, C. and Dimitriou, P. Doses to operators during interventional radiology procedures: focus on eye lens and extremity dosimetry. Radiat. Prot. Dosim. 144(1 – 4), 482 – 486 (2011). 17. Huyskens, C. J., Franken, Y. and Hummel, W. A. Guidance on personal dosimetry for occupational exposure in interventional radiology. J. Radiol. Prot. 14, 229 –234 (1994).
doi:10.1093/rpd/ncu148
INFLUENCE OF STANDING POSITIONS AND BEAM PROJECTIONS ON EFFECTIVE DOSE AND EYE LENS DOSE OF ANAESTHETISTS IN INTERVENTIONAL PROCEDURES Y. Kong1, L. Struelens2, F. Vanhavere2, C. S. Vargas2, W. Schoonjans2 and W. H. Zhuo1, * 1 Institute of Radiation Medicine, Fudan University, Xietu Road 2094, Shanghai 200032, China 2 Radiation Protection Dosimetry and Calibration, Belgian Nuclear Research Centre, SCK.CEN, Boeretang 200, Mol 2400, Belgium
Received 27 January 2014; revised 2 April 2014; accepted 4 April 2014 More and more anaesthetists are getting involved in interventional radiology procedures and so it is important to know the radiation dose and to optimise protection for anaesthetists. In this study, based on Monte Carlo simulations and field measurements, both the whole-body doses and eye lens dose of anaesthetists were studied. The results showed that the radiation exposure to anaesthetists not only depends on their workload, but also largely varies with their standing positions and beam projections during interventional procedures. The simulation results showed that the effective dose to anaesthetists may vary with their standing positions and beam projections to more than a factor of 10, and the eye lens dose may vary with the standing positions and beam projections to more than a factor of 200. In general, a close position to the bed and the left lateral (LLAT) beam projection will bring a high exposure to anaesthetists. Good correlations between the eye lens dose and the doses at the neck, chest and waist over the apron were observed from the field measurements. The results indicate that adequate arrangements of anaesthesia device or other monitoring equipment in the fluoroscopy rooms are useful measures to reduce the radiation exposure to anaesthetists, and anaesthetists should be aware that they will receive the highest doses under left lateral beam projection.
INTRODUCTION During X-ray guided interventional radiology procedures, medical staff are exposed to high radiation dose since they work in a fluoroscopy room with large amount of scattered radiation. The primary operators who usually stay longer and stand closer to the patient’s right side are most likely to receive the highest exposure among all staff involved in interventional procedures. The radiation exposure to the primary operator has been widely investigated and measures of radiation protection were also recommended(1 – 4). With the rapid popularisation and development of new techniques in interventional radiology, more and more anaesthetists who operate the anaesthesia device and check other monitoring equipment are involved in the clinical procedures for the patient care. During interventional procedures, the anaesthetists usually stay shorter time in the fluoroscopy room than the primary operators. It was thought that their radiation exposure would be lower than the primary operators. However, recent surveys indicated that their exposure could also be relatively high. Anastasian et al. (5) found that the averaged radiation exposure to anaesthetists’ face was .3-fold of the exposure to radiologists in the neurointerventional suite. Ismail et al. (6) reported that the averaged dose to anaesthetists was 0.28 mSv for an endoscopic retrograde cholangiopancreatography procedure and 2.32 mSv in cardiac catheterisation
suite over 6 months. Routine monitoring of radiation for anaesthetists working in the cardiac catheterisation laboratory was also suggested by Henderson et al.(7). Compared with the primary operators, the anaesthetists usually stand on the left side or the head side of the patients, and their standing positions are more flexible. It is thought that their exposure can be reduced by changing their standing positions and trying to avoid the main scattered radiation according to the X-ray beam projections. In this work, based on Monte Carlo simulations, both the effective dose and eye lens dose of anaesthetists were calculated under different irradiation conditions. The effect of four standing positions of anaesthetists and some common beam projections on the effective dose and eye lens dose were studied and partially compared with field measurements. Furthermore, the correlations between the eye lens dose and personal dose equivalent HP(10) over apron were also estimated.
MATERIALS AND METHODS Simulations For Monte Carlo simulations, the software MCNPX version 2.5.0 was used(8). Similar scenarios, which were observed during the field measurements of this study for anaesthetists were simulated in the Monte Carlo set-up. A modified ORNL-MIRD phantom(6, 9)
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Western Ontario on June 9, 2015
*Corresponding author: [email protected]
Y. KONG ET AL.
The number of simulated source photons was set to be 108 for all simulations. Assuming the organ factors including size and density to be constant, the uncertainty of the effective dose or HP(3) was propagated from the uncertainty of calculated organs/tissue doses. The uncertainty of effective dose was ,5 %, and the uncertainty HP(3) was generally ,10 %. Measurements Field measurements were carried out for 12 neurology (INR), 10 radiofrequency ablation (RFA) and 9 vertebroplasty interventional procedures in two Belgian hospitals. Information including the standing positions of anaesthetists, total KAP, exposure time and shielding facilities was also recorded during the measurements. For each procedure, the eye lens dose of anaesthetists TM was measured by the Eye-D dosemeter(11) which was calibrated against HP(3). This dosemeter is composed of an MCP-N (LiF:Mg,Cu,P) type of thermoluminescent detector (TLD) and an optimised polyamide capsule. The lower limit of detection (LLD) for the dosemeter was estimated as twice its background variation (2sBG). Four chips of the TLDs were kept in the laboratory as background control. If the readout value of the TLD was lower than the LLD, the value was recorded as half of the LLD value(12). For each procedure, four DIS-1 dosemeters(13) were used to monitor the personal dose equivalent HP(10) at the level of the neck over the thyroid collar, the waist over the apron and the chest level over and under the apron. DIS dosemeters were positioned on the side facing the X-ray tube. Therefore, in cases where the anaesthetist turned away from the X-ray tube, the DIS was positioned on his back. The effective dose was estimated with different single and double-dosimetry algorithms for interventional radiology personnel, with the HP(10) measured at the neck over the thyroid collar and chest level under the apron. These results are also compared with the calculated effective doses. Additionally, correlations between eye lens dose and HP(10) values over apron at those three sites were also explored, respectively. The DIS detector was tested within the ORAMED project in a scattered radiation field, and its overall uncertainty was 20 % (2s)(14). For TLDs, a 20 % (2s) measurement uncertainty was also considered(15). RESULTS AND DISCUSSION Calculated effective dose
Figure 1. Four main standing positions of anaesthetists in interventional procedures.
The normalised effective dose (E/KAP) of an anaesthetist in different conditions of standing positions and beam projections were calculated and are shown in Figure 3. As shown in Figure 3, the normalised effective doses depend not only on the standing
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was used as a patient and the reference male voxel phantom(10) was used to represent an anaesthetist. In all simulations, the anaesthetist wears a 0.5-mm Pb lead apron, which fits well to the body with a thyroid shield. An X-ray spectrum corresponding to a tube voltage of 80 kVp with a filtration of 3 mm Al was used. The X-ray photons were supposed to emit from a point source and collimated into a cone with a field diameter at the entrance of the image intensifier of 40 cm and the distance from source to detector was fixed to 90 cm. The image intensifier was simplified to be a radiation absorber and the thickness of the window was set to be 1.5 mm Al. The four mostly observed standing positions of anaesthetists in the field measurements of this study are illustrated in Figure 1 and the X-ray beam projections are illustrated in Figure 2. For the head irradiation, seven X-ray beam projections were considered, namely as posterio-anterior (PA), right anterior oblique (458RAO), left lateral (LLAT), right lateral (RLAT), left anterior oblique (458LAO), caudal (308CAUD) and cranial (308CRAN). For the thorax irradiation, five projections were considered, i.e. PA, 458RAO, 458LAO, LLAT and RLAT. The energy deposition in different organs or tissues was calculated by using F6 tally in the MCNP code in the voxel model representing anaesthetists. Based on the calculated organ doses and the tissue weighting factors recommended in ICRP 103, the effective dose was summed up over the equivalent doses for all organs and tissues. Eye lens dose was calculated in a small volume of 3-mm depth at the eye positions to represent HP(3). As the simulation results of MCNPX were normalised by the number of simulated particles in order to compare the results with the measured quantity, the calculated doses were further normalised to the kerma area product (KAP) in this work. Therefore, along the beam axis, a thin air layer between the X-ray focal spot and patient was constructed to simulate the KAP value, which is the product of the air kerma to the layer and the area of the X-ray beam on the layer.
ANAESTHETIST DOSE IN INTERVENTIONAL PROCEDURES
Figure 3. Effective dose of anaesthetists calculated under different conditions: (a) head irradiation and (b) thorax irradiation.
positions, but also on the beam directions. For the head irradiation, the highest dose of 0.096 mSv (Gy21 cm22) at the P-2 position under LLAT projection is 12 times higher than the lowest of 0.007 mSv (Gy21 cm22) at the P-4 position under 458LAO. While for the thorax irradiation, the highest of 0.156 mSv (Gy21 cm22) at the P-3 position under LLAT projection is 13 times higher than the lowest of 0.011 mSv (Gy21 cm22) at the P-4 position under 458LAO. For the head irradiation, the effective doses at P-1, P-2, P-3 and P-4 were averaged to be 0.059, 0.046, 0.035 and 0.016 mSv (Gy21 cm22) for the seven different beam projections, respectively. For the thorax irradiation, the doses at P-1, P-2, P-3 and P-4 were averaged to be 0.037, 0.042, 0.059 and 0.033 mSv (Gy21 cm22) for the five different beam projections, respectively. The results are reasonable because P-1 for the head irradiation and P-3 for the thorax irradiation are closer to the centre of radiation fields than the position of P-4. Therefore, in order to reduce the radiation exposure to anaesthetists, it is suggested to set the anaesthesia device and other monitoring equipment as far away from the bed as possible
provided the changes of positions do not affect the patient care during the interventional procedures. Furthermore, it is found that the doses to anaesthetists at the same position are always the highest under LLAT projections among the different beam projections. It suggests that the anaesthetists should avoid staying at their positions when the beam is on with the LLAT projection. However, from the viewpoint of radiation exposure, the LLAT projection is generally preferable for primary operators(5, 16). Therefore, under the instructions of primary operators, a selection of a reasonable time to enter the fluoroscopy room can also reduce the radiation exposure to anaesthetists. Calculated eye lens dose The normalised eye lens dose (HP(3)/KAP) of an anaesthetist in different conditions of standing positions and beam projections were calculated and are shown in Figure 4. As shown in Figure 4, the normalised eye lens doses depend on not only the standing positions, but also on the beam directions. For the head
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Figure 2. Simulated X-ray beam projections in head or thorax irradiation.
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Table1. Comparisons among effective doses derived from different algorithms for 12 INR procedures. Algorithma
Positions of dosemeters Single dosimetry Huyskens et al. (1994 )(17) (18)
McEwan (2000)
Double dosimetry Wambersie et al. (1993)(19) (18)
McEwan (2000)
Clerinx et al. (2008)(20) von Boetticher (2010) a
Effective doseb (mSv (Gy21 cm22))
Hu: trunk under apron Ho: trunk over apron Hu: trunk under apron Ho: collar over shield
E ¼ 3 Hu E ¼ 0.2 Ho E ¼ 2 Hu E ¼ 0.08 Ho
0.046 (0– 0.097) 0.049 (0.003– 0.121) 0.031 ( 0 –0.065) 0.009 (0.001– 0.032)
Hu: chest under apron Ho: neck/shoulder over shield Hu: trunk under apron Ho: collar over shield Hu: chest under apron Ho: neck over shield Hu: chest under apron Ho: neck over shield
E ¼ Hu þ 0.1Ho
0.027 (0.003– 0.057)
E ¼ 0.71Hu þ 0.05Ho
0.017 (0.001– 0.035)
E ¼ 1.64Hu þ 0.075Ho
0.034 (0.002– 0.070)
E ¼ 0.84Hu þ 0.051Ho
0.019 (0.001– 0.039)
Hu and Ho represent HP(10) under or over apron/thyroid shield. Dose value is exhibited as mean (min –max).
b
irradiation, the highest dose of 2.228 mSv (Gy21 cm22) at P-1 under RLAT projection is .500 times higher than the lowest of 0.004 mSv (Gy21 cm22) at P-2 under 458LAO. While for thorax irradiation, the highest dose of 2.399 mSv (Gy21 cm22) at P-1 under RLAT projection is nearly 200 times of the lowest of 0.012 mSv (Gy21 cm22) at P-2 under 458LAO. Under different beam projections, the averaged eye lens doses are 1.305, 0.278, 0.555 and 0.281 mSv (Gy21 cm22) at P-1, P-2, P-3 and P-4 for the head irradiation, and 1.209, 0.321, 0.955 and 0.522 mSv (Gy21 cm22) for the thorax irradiation, respectively. The dose at P-1 presents the highest dose among the four positions. It suggests that the anaesthetists should avoid staying at P-1 during the interventional procedures and facing to the patients. Furthermore, it is also found that the eye lens doses of anaesthetists are generally much higher under LLAT or RLAT projections than under other beam projections. It also suggests that the anaesthetists
should avoid staying at their positions when the beam is on with the LLAT or RLAT projections. Comparisons By applying the algorithms for the estimation of the effective dose suggested by other researches, the effective doses for anaesthetists during INR procedures were calculated and is shown in Table 1. As listed in Table 1, compared with single dosimetry (SD), more narrow ranges of effective dose values are found with the double dosimetry (DD). It implies that the DD will give a more stable result, while the SD is more likely to lead to a larger deviation. For the averaged dose, different algorithms lead to a maximal difference by a factor of over 5. As these algorithms were suggested for main operators during interventional procedures, further studies are still needed to provide a more accurate algorithm to estimate the effective dose of anaesthetists.
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Figure 4. Eye lens dose of anaesthetists calculated under different conditions: (a) head irradiation and (b) thorax irradiation.
ANAESTHETIST DOSE IN INTERVENTIONAL PROCEDURES Table 2. Comparisons between the simulated and measured dosea.
Measurement INR (head) Vertebroplasty (thorax) RFA (thorax) Simulation INR (head) Vertebroplasty (thorax) RFA (thorax)
No.
Positions
Effective dose, mean (range)
Eye lens dose, mean (range)
12 9 10
P-2, P-3, P-4 P-2, P-3 P-1
0.019 (0.001– 0.039) 0.071 (0– 0.159) 0.092 (0– 0.268)
0.384 (0.093– 1.353) 0.592 (0.144– 1.337) 2.208 (0.504– 5.422)
P-2, P-3, P-4 P-2, P-3 P-1
0.032 (0.007– 0.096) 0.050 (0.013– 0.156) 0.037 (0.024– 0.056)
0.371 (0.004– 1.287) 0.638 (0.012– 2.246) 1.209 (0.536– 2.399)
a
During this study, both the effective dose and eye lens dose for .30 anaesthetists were monitored. For easy comparisons, both the simulated and measured doses were normalised to the KAP first, and then the comparison result is listed in Table 2. As seen from Table 2, simulated doses are in a reasonable range compared with measured ones. The variances may arise from the different dimensions between the standard voxel phantom and the anaesthetists. Moreover, the exact position and movement of the anaesthetist are also hard to be accurately simulated. As shown in Table 2, the normalised dose in average differs from the procedure types, with the highest for the RFA procedure. Moreover, even for the same type of procedure, the dose also obviously varies among different measurements. Anaesthetists were not always in the fluoroscopy room, they entered the room only when needed during the procedure. Besides the total exposure time for anaesthetists were different, the beam projections were not necessary the same when they entered the rooms. However, the authors still have a strong impression that if the anaesthetist stayed significantly longer, their doses are higher. The eye lens dose of the anaesthetists was averaged to be 68 mSv per INR procedure in this study. It was 10 times higher the value (6.5 + 5.4 mSv) in similar quantity (exposure to the face) reported by Anastasian et al. (5). In Anastasian’s study, there was a shield between the anaesthetist and fluoroscopy equipment, while there was not any protection shield for the anaesthetists in this work. It indicates that an additional shield set between the anaesthetist and fluoroscopy equipment may significantly reduce the eye lens dose of anaesthetists. Correlation between the eye lens dose and HP(10) measured at other points Figure 5 shows the results of the eye lens dose HP(3) and HP(10) over apron at neck, chest and waist level measured for the 30 anaesthetists in this work. Fitted
by the least squares method by using the software Origin 9.0, fairly good correlations between the HP(3) and HP(10) at neck, chest or waist could be observed. Recently, through a simulated anthropomorphic study, Farah et al.(21) has also reported that the HP(3) correlates best with HP(10) at left collar level for main operators. It indicates that the eye lens dose of the anaesthetists can also be estimated by other monitoring results usually performed. Based on the measurement results and an assumed annual workload of 200 procedures for an anaesthetist, the annual averages of the effective dose and eye lens dose were estimated to be 0.44 mSv and 8.8 mSv, respectively. The effective dose was much smaller than the value reported by Ismail et al.(6). The main reason was thought that the algorithm used here to estimate the dose to anaesthetists was different. However, the eye lens dose was still relatively high. It indicates that more attention should be paid to protect the eye lens even though the effective dose is not so high. CONCLUSION In this study, based on Monte Carlo simulations and field measurements, both the effective dose and eye lens dose of anaesthetists in some interventional procedures were studied. The results showed that the radiation exposure to anaesthetists depends not only on their standing positions, but also on the beam projections used during interventional procedures. In general, a close position to the bed and the left lateral (LLAT) beam projection will deliver a higher exposure to anaesthetists. The eye lens dose of an anaesthetist may reach several tens of microSieverts in a single procedure. Reducing stay time in the fluoroscopy room, enlarging distance and radiation shield can reduce their radiation dose. Adequate arrangements of anaesthesia device or other monitoring equipment in the fluoroscopy rooms are useful measures to reduce the radiation exposure to anaesthetists. Anaesthetists should be aware to avoid to enter the
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The unit of dose is in mSv (Gy21 cm22). Measured effective doses were estimated based on von Boetticher’s algorithm (2010). The simulated doses were summarised over seven and five beam projections for head and thorax irradiation, respectively.
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further research works are still needed to study the effects of different thicknesses of the lead apron and the X-ray filtration, different postures of the anaesthetist at work, and so on.
FUNDING The work was partially supported by the National Natural Science Foundation of China (grant no. 11075040).
Figure 5. Correlation between the eye lens dose HP(3) and HP(10) at neck, chest and waist over aprons.
room when the X-ray beam is on under the LLAT beam projection. The eye lens dose of anaesthetists can be roughly estimated from the doses measured at the neck, chest or waist by using routinely used personal dosemeters. For more accurate estimations of the radiation exposure to anaesthetists in the interventional procedures,
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