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1 Angiocardiographic Suite, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, 2 Northern Ireland Medical Physics Agency, Forster Green Hospital, 110 Saintfield Road, Belfast BT8 4HD and 3 University of Ulster at Jordanstown, Shore Road, Newtownabbey, County Antrim, BT37 OQB, UK
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Abstract |
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Introduction |
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Although the RF ablation procedure is effective, it is not without risks [2–4]. Some of these risks arise from the use of ionizing radiation during the procedure, in the form of fluoroscopy X-rays, which are used to guide intervention. The patient is exposed to the X-ray fluoroscopy beam and, because some of the X-rays are scattered from the patient, staff who are positioned around the patient are also exposed to scattered radiation, but to a lesser extent than the patient. The doses of ionizing radiation patient and staff receive places each at risk of suffering detrimental effects, the level of risk depending on the size of dose received by the individual. Detrimental effects, such as malignant disease in those exposed and inherited defects in later generations, are stochastic effects for which it is assumed that there is no threshold dose. For low doses, the risk of occurrence is proportional to the dose received. Some other detrimental effects only occur at relatively high doses of radiation and there is a threshold below which each effect does not occur. As the dose increases above the threshold, the probability of observing the effect increases rapidly. These are termed deterministic effects and include erythema to the skin, sterility and cataracts. RF ablation procedures can be complex and can involve the use of long fluoroscopy times. There is consequently a potential for high radiation doses to patients and staff compared with other X-ray examinations.
Interventional procedures involving short periods of fluoroscopy place patients predominantly at risk of suffering stochastic effects such as malignant disease. However, in recent years concern has been raised about the risk of patients suffering skin injury, a deterministic effect, from X-ray exposure during lengthy interventional cardiology procedures such as RF ablations. The dose of ionizing radiation received by patients during RF ablations can be among the largest from medical applications other than those from radiation oncology [5–8]. The literature contains a number of reports of skin injury [9–15]. Data from the US Food and Drug Administration (FDA) described 21 cases of skin lesions on patients who had undergone interventional radiological procedures [9]. Almost half of these were owing to cardiac RF ablations.
X-ray radiation generated during fluoroscopy is attenuated rapidly in tissue, so the maximum dose is delivered to the skin at the point the X-ray beam enters the patient. Owing to this, skin will probably suffer injury before other internal organs are affected [16]. Injury to skin is deterministic in nature, as there is a threshold below which the effect is not observed. As the dose increases above the threshold the probability of observing the effect increases rapidly. Guidance regarding threshold doses for deterministic effects to skin has been given by the International Commission on Radiological Protection (ICRP) [17, 18] and the National Radiological Protection Board (NRPB) [19, 20] and is presented in Table 1
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The risks to patients arising from exposure to ionizing radiation during RF ablations can be compared with the benefits to the patient from this procedure and with risks from alternative treatment strategies in order to provide justification for the RF ablation procedure. Jaeggi et al [22] highlight the use of the anti-arrhythmic drug adenosine for acute treatment of common types of SVT because of its efficacy and safety. However, there have been a few reports of serious proarrhythmic events associated with its use, including the induction of atrial fibrillation. Connolly [23] stated that a decreased mortality with certain anti-arrhythmic drugs remains unproven and in some cases there is evidence of increased mortality with class I and class III agents. Also, in a study by Hogenhuis et al [24], it was assumed that the annual risks of cardiac arrest for patients with Wolff–Parkinson–White syndrome between the ages of 20 years and 60 years are 0.01%, 0.05% and 0.5%, respectively, in patients who are asymptomatic, who had paroxysmal supraventricular tachycardia (PSVT) or atrial fibrillation (AF) without haemodynamic compromise, or who had PSVT or AF with haemodynamic compromise. This assumption was based on a Markov simulation model and included the risks of cardiac arrest, PSVT or AF, drug side effects, procedure-related complications and mortality, the efficacy of drugs and RF ablation, and costs. It was predicted that RF ablation has an overall efficacy of 92% in preventing cardiac arrest and arrhythmias, and should yield a life expectancy greater than or equal to other strategies. The study also suggested that RF ablation should prolong survival and save resources in cardiac arrest survivors and patients who have had PSVT or AF, with haemodynamic compromise.
Operators using fluoroscopy during interventional procedures are at risk from the radiation scattered from the patient. The operator is exposed to only a small fraction of the dose received by the patient but, over a period, it can accumulate to a significant dose of radiation. The risk to the operator, as for patients, can be both stochastic and deterministic in nature. Regulatory bodies set dose limits for workers involved in the use of ionizing radiation. The dose limit for whole body irradiation is based on the tolerable risk to an individual of suffering stochastic effects. Dose limits for extremities and for the lens of the eye are based on the dose thresholds at which deterministic effects occur after prolonged exposure. Several cases of ophthalmologically confirmed lens injuries caused by occupational exposure to radiation during interventional radiological procedures have been reported [25]. It was estimated that doses to eyes in these cases ranged from 450–900 mSv per year over several years, which exceeds the threshold for lens opacities.
The aims of this study were to measure the dose of ionizing radiation received by the patient and operator during RF ablations in an angiocardiography suite and to assess the subsequent risk to those individuals. A directive from the European Council laying down measures for the protection of patients undergoing medical exposures [26] introduced a requirement for the establishment of diagnostic reference levels (DRLs) for each standard radiological investigation. This requirement has been implemented in UK legislation [27]. The regulations also require special care to be taken in the optimization of medical exposures involving a high dose to the patient. A further aim of this study was to investigate the possibility of locally adopting a DRL for the RF ablation procedure.
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Methods |
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Measurement of fluoroscopy equipment performance
Equipment performance tests were initially carried out to determine if the fluoroscopy equipment was performing at a satisfactory level. Performance testing of the fluoroscopy equipment was in accordance with the Institute of Physics and Engineering in Medicine Report 77 [28] and followed methods similar to those described in established protocols [29, 30]. Input dose rate to the image intensifier was measured with 2 mm of Cu in the beam at the X-ray tube. Dose rate at the surface of a 20 cm thick Perspex phantom set on the patient couch at the typical operating position (tube focus to image intensifier distance 94 cm, tube focus to phantom surface distance 70 cm) was also measured. All dose rate measurements were made with the automatic exposure control set up as used clinically, and with the antiscatter grid in place, and were measured by a Keithley Model 35050A dosemeter (Keithley Instruments Inc., Cleveland, OH), which had a calibration traceable to the Physikalisch-Technische Bundesanstalt (PTB) primary standard.
RF ablation protocol
Two experienced electrophysiologists performed the RF ablation procedures. The same electrophysiology laboratory and fluoroscopy equipment were employed throughout the study; a Siemens Polydoros 100 single plane fluoroscopy unit with a Coroskop C rotational C-arm and an Optilux 27HD-Triplex image intensifier (Siemens, Erlangen, Germany). The X-ray tube was routinely used in the undercouch position. The electrophysiologist carrying out the procedure stood at the patient's right side and wore a lead apron and thyroid collar during the procedures. A portable lead shield was positioned between the physician and the patient. Magnified views were used sparingly, i.e. the full image intensifier field size of 27 cm was used routinely throughout the procedure. This occasionally changed to the magnified field size of 17 cm for ease of visualization in difficult circumstances or to position catheters. The only projections employed were left anterior oblique 30° (LAO), right anterior oblique 30° (RAO) and posteroanterior (PA). The radiation field was collimated tightly to the area of interest throughout each procedure. For the PA projection the X-ray beam entered the patient's back, for the LAO projection the X-ray beam entered the right side of the patient's back and intercepted the image intensifier at the left front side of the patient, and for the RAO projection the X-ray beam entered the left side of the patient's back and intercepted the image intensifier at the right front side of the patient.
A detailed diagnostic study was performed in all patients prior to ablation to confirm the presence of the electrophysiological mechanism of arrhythmia. The patient sample included patients with accessory pathways, AV node re-entrant tachycardia, atrial tachycardia, atrial flutter, ventricular tachycardia and AF that required ablation of the AV node. The electrophysiological study (EPS) protocol was carried out using three 6 F quadripolar catheters (BARD, Crawley, UK; Cordis, Ascot, UK) with 1 cm interelectrode spacing inserted into a femoral vein and positioned into the right atrium, His bundle and right ventricle. A decapolar catheter (Daig, Minnetonka, MN) was inserted via the right or left jugular vein into the coronary sinus. The EPS studied the baseline electrophysiological properties, the inducibility of tachyarrhythmias and mapped the locations of the accessory pathway or re-entrant circuits to a general region of the heart. Once the accessory AV connection was located, mapping the targeted region was performed with the ablation catheter, a 7 F quadripolar electrode catheter with a 4 mm distal electrode (Medtronic Marinr, Watford, UK), and BARD Stinger catheters were used. Typically this was achieved by positioning the ablation catheter against the mitral or tricuspid annulus in the area identified during preliminary mapping. Catheter ablation was performed using radiofrequency energy delivered at 40–50 W. A temperature of approximately 65°C was achieved at impedance of approximately 100 ohms.
Measurement of dose to the electrophysiologists
Staff dose was routinely monitored in the electrophysiology laboratory using dosemeters supplied by a dosimetry service approved by the UK Health and Safety Executive. This approved dosimetry service assesses effective dose to an individual as being adequately indicated by the personal dose equivalent, penetrating Hp(10), measured by a film badge containing Type 2 Kodak Personal Monitoring Film (Kodak, Hemel Hempstead, UK) worn under the individual's protective lead apron. Additionally, equivalent dose to the lens of the eye and extremity skin dose is assessed as being adequately indicated by the personal dose equivalent, superficial Hp(0.07), measured by NE Bicron Extremity thermoluminescent dosemeters (TLDs) (Bicron-NE, Solon, OH) worn on the forehead and hand. Each electrophysiologist routinely wears a film badge at waist height under a protective apron of 0.25 mm lead equivalence to measure the effective dose received from their occupation. They also routinely wear extremity TLDs on the forehead and left hand, to provide a measure of the equivalent dose to the lens of the eye and the extremity skin dose. As part of this study, an extra film badge and pair of extremity TLDs were worn in the same positions by each electrophysiologist only during the RF ablation procedures for which they acted as operator. This allowed the dose per RF ablation procedure to be compared with the mean dose for the rest of the cardiology procedures carried out in the centre. The film badges and extremity TLDs were replaced each month with new dosemeters. The uncertainty associated with both the film badge and extremity TLD measurements was ±20% (95% confidence). The minimum detectable dose was 0.15 mGy for both types of dosemeter.
Measurement of patient dose
Measurements of absorbed dose to the patient's skin were made for each patient using two TLDs taped to the body before the EPS and RF ablation procedure. It was considered that maximum skin dose for any patient was likely to be along the spine as the RAO, LAO and PA projections overlapped along the spine when imaging with the full field of the image intensifier, and so TLDs were positioned at the thoracic vertebra 9 and 11. Radio-opaque pointers were used during the initial stages of the procedure to ensure the TLDs lay in the primary X-ray beam once the working position had been determined. For each patient, the greater dose recorded by either of the TLDs used for that patient was regarded as the patient's skin dose. The TLDs used were LiF:Mg,Cu,P (TLD-100H) dosemeters from HarshawTLD (Bicron-NE, Solon, OH) and were calibrated in terms of absorbed dose to air at diagnostic X-ray energies (60–120 kV) using the Keithley Model 35050A dosemeter described previously. The uncertainty associated with these dose measurements was estimated to be ±12% (95% confidence level).
The dose–area product (DAP) received by the patient was recorded for each procedure using a PTW Diamentor (PTW, Freiburg, Germany) DAP meter. This DAP meter was calibrated at diagnostic X-ray qualities using a Radcal 1015C X-ray monitor with a 10x5–6 ionization chamber (Radcal Corporation, Monrovia, CA), which had a calibration traceable to the PTB primary standard. It has been recognized that the response of a DAP meter, i.e. the indicated value divided by the true DAP at the surface of the patient, will depend on whether the DAP chamber is installed on an overcouch or an undercouch X-ray tube [31]. The DAP chamber used during the current study was installed on a fluoroscopy C-arm that can be used in overcouch and undercouch positions, and the installer had adjusted it to accurately measure the DAP at the surface of the patient when the X-ray tube was in the overcouch position. Measurements using the Radcal 1015C X-ray monitor showed that the patient couch attenuated the primary X-ray beam to 70% of its original intensity. As the X-ray tube was used in the undercouch position for all of the beam projections used during the RF ablation procedures, the DAP indicated by the meter was subsequently multiplied by 0.7 to indicate the true DAP at the surface of the patient. In the present study results are presented in terms of the DAP at the surface of the patient. Uncertainty associated with the DAP meter readings was ±10% (95% confidence).
The type of RF ablation, fluoroscopy time, fluoroscopy kilovoltage (kV), patient age and weight were also recorded for each procedure. Patients were examined at 12 week follow-up and checked for any evidence of skin injury.
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Results |
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Fluoroscopy equipment performance
Results of the fluoroscopy equipment performance tests are shown in Table 2. When compared with the observed variation in a sample of results from NHS units [29], this image intensifier, when in full field mode, has a dose rate to the image intensifier that lies in the lower half of NHS systems. The phantom surface dose rate is classed as low when compared with the reported performance of other fluoroscopy units [30].
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. It should be noted that no effective dose was recorded for electrophysiologists as each month's film badge was below the minimum detectable dose. The equivalent dose to the hand and forehead per RF ablation procedure was at least twice the mean dose for other cardiology procedures. The mean equivalent dose to the left hand and forehead for other interventional cardiology procedures in the present study is considerably smaller than that reported by Vano et al [32] for cardiologists using a protective lead screen (0.24 mSv to the left hand, 0.15 mSv to the forehead). The staff doses measured for the other cardiology procedures in the current study will of course depend on the types and numbers of procedures carried out by the electrophysiologists. An indication of the types and frequencies of other procedures carried out is given in Table 5 and Table 6.
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Standard coronary angiography projections are acquired at 12.5 frames per second. For the left coronary artery they typically include: shallow RAO 20°; RAO 30°, 25–30° caudal; RAO 30°, 25–30° cranial or PA cranial 40°; LAO 45°, 25–30° cranial; lateral; and LAO 45°, 25–30° caudal. For the right coronary artery they typically include: LAO 45°, 25° cranial; lateral; and RAO 30°. Aortograms and left ventriculograms are imaged in the RAO 30° projection and are acquired at 25 frames per second.
The duration of fluoroscopic screening is dependent on the complexity of the procedure and whether any complications are encountered. Any number of the above projections can be used at random to help visualize an area of interest. Hence, radiation doses vary greatly between procedures.
Patient dose
Results of the patient dose measurements are shown in Table 4 for the different types of RF ablation procedure and the combined results for all RF ablation procedures. The sample consisted of 50 patients, 33 (66%) male and 17 (34%) female, ranging in age from 14 years to 84 years (mean 43 years, median 45 years). The results show that fluoroscopy time and radiation dose varied according to the location of the tachycardia. AV node ablation and modification procedures were found to have a significantly lower skin dose than the other procedures. Atrial flutter and left-sided accessory pathways that required a trans-septal approach had longer examination times and yielded the maximum radiation doses. The type of RF ablation catheter used did not appear to alter examination duration or radiation exposure.
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and Table 6. From the differences in mean DAP and fluoroscopy time for the various procedures, it can be seen that the less frequent procedures are also the most complex procedures and have a DAP and fluoroscopy time similar to that of RF ablation procedures.
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Discussion |
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Recommendations of the National Council on Radiation Protection and Measurements (NCRP) [37] suggest that two dosemeters, both measuring personal dose equivalent, penetrating Hp(10), should be used, one over and one under the lead apron. A weighted average of the two measured doses should be taken as an estimate of the effective dose. This method is intended to provide an overestimate of the effective dose and is said to result in a factor of overestimation of between 1.2 and 2.0 for a 0.3 mm lead apron.
The ICRP state that the overall uncertainty (95% confidence) in the estimation of effective dose around the relevant dose limit may well be a factor of 1.5 in either direction for photons, and greater uncertainties are inevitable at low dose levels [35]. Under the conditions encountered during the current study (a single film badge worn at the waist under a 0.25 mm lead apron during fluoroscopy of 75 kV), effective dose may have been underestimated by a factor of 3 or 4 [36]. As the effective dose measured for each electrophysiologist was low during routine monitoring of the current study, it would probably not be appropriate to implement the additional monitoring recommended by the NCRP. The low effective doses measured imply that stochastic risks to the electrophysiologists are commensurately low. Results from the present study highlight that good radiation protection practice and awareness can be effective in limiting occupational exposure. However, in other centres, with different protocols and with use of different protective tools, staff doses may not be limited to the same extent.
Risk to electrophysiologists: deterministic effects
The limit on equivalent dose for occupationally exposed individuals is 150 mSv per year for the lens of the eye, and 500 mSv for the skin or hands [33, 34]. It has already been stated that the equivalent dose to the lens of the eye and extremity skin dose in the current study was assessed as being adequately indicated by the personal dose equivalent, superficial Hp(0.07), measured by TLDs worn on the forehead and hand. The largest annual equivalent dose to the lens of the eye and the skin of the hands for either of the electrophysiologists (the sum of the annual dose from RF ablation and other procedures in Table 3
) was 3.6 mSv and 28.8 mSv, respectively. It is clear that the estimated annual doses received by the electrophysiologists in the current study are well below the occupational dose limits, and they are at little risk of suffering deterministic effects such as lens opacities.
Risk to patient: stochastic effects
Conversion coefficients for deriving effective dose from measurements of DAP and fluoroscopy tube potential (kV) have been developed by the NRPB [38]. These were used to calculate the effective dose for each patient. The mean effective dose for a RF ablation procedure was 17 mSv. This is comparable with the mean effective dose of 17.3 mSv for RF ablation procedures reported by Broadhead et al [5]. Using risk coefficients from the NRPB [39], the excess risk of developing fatal cancer from this dose is calculated to be approximately 1 in 1000 (0.1%). This is similar to results from other studies [6, 7, 40] in which the estimated increased risk of developing fatal cancer from the mean effective dose varied from 0.1% to 0.2%. The mean effective dose of 17 mSv can be put into perspective by comparing it with the effective dose of 10 mSv from an average abdomen CT [41]. The maximum effective dose received by a RF ablation patient in the current study was 77 mSv and the excess risk of developing a fatal cancer from this dose is approximately 1 in 200 (0.5%).
Risk to patient: deterministic effects
The maximum skin dose measured on any patient was 3.2 Gy. This exceeds the threshold dose for transient erythema (2 Gy) but is below the threshold doses of 6 Gy and 10 Gy for more serious effects such as main erythema and moist desquamation. Six of the 50 patients included in the study (12%) received a skin dose of more than 2 Gy, exceeding the minimum threshold levels for transient erythema. This is comparable with a study by Rosenthal et al [40], in which 20% of patients exceeded the threshold for skin injury. No clinical manifestations of radiodermatitis were evident at the 12 week follow up and there were no reports of any adverse effects from patients. This shows that most patients are unlikely to suffer serious injury from RF ablation procedures in this electrophysiology laboratory under current working protocols.
Although none of the patients in this study suffered serious effects, the measured doses indicate that patients could be at risk of suffering skin injury from unusually difficult and prolonged procedures. From Table 4 it is clear that the maximum skin dose measured for any patient was four times greater than the mean skin dose, demonstrating that the dose distribution is skewed and, occasionally, a very difficult procedure could give an anomalously high and dangerous skin dose. Therefore it would be prudent to devise a working protocol that would provide the electrophysiologist with an indication during the procedure when patient skin dose was approaching certain threshold levels, and that the patient was at risk of suffering skin injury. This would allow the electrophysiologist to make an informed decision as to whether to continue with the procedure.
Method for monitoring skin dose during RF ablation procedures
A limitation of the method for measuring skin dose used in the current study is that it is possible, and indeed likely, that the TLDs positioned at the thoracic vertebrae were not in the primary X-ray beam for some of the projections during the procedure. We initially considered that the maximum skin dose for any patient was likely to be along the spine as the RAO, LAO and PA projections overlapped along the spine when imaging with the full field of the image intensifier. As such, TLDs were positioned on the thoracic vertebrae. However, a discrete number of measurements of entrance surface dose over the patient's skin does not provide an absolute measure of the maximum skin dose, as the overlapping projections are likely to make a complex pattern of irradiation over the skin [42]. The pattern of irradiation will depend on several factors, such as the number of projections used, the geometry of each projection and the degree of beam collimation for each projection. Measurements of skin dose made during this study are therefore estimates of the maximum skin dose received by the patient. Nevertheless, the measured skin doses are probably sufficient to show if patients are at risk of acute skin injury from undergoing RF ablation in this centre. Also, the close correlation between DAP and skin dose found during the current study demonstrates that this method of dose measurement allows the DAP to be used as a rough and simple guide to the maximum skin dose a patient is likely to receive from this procedure in this centre.
It has already been stated that the pattern of dose on the patient's skin depends on several factors. This can be illustrated by considering the use of the magnified field (17 cm) instead of the full field (27 cm) for any given projection. For the fluoroscopy unit, when changing from full field to magnified field, the DAP per unit fluoroscopy time is halved, but in contrast the dose rate to the patient's skin is increased by about 50% (see Table 2). It is clear that the magnitude and distribution of skin dose is strongly dependent on the particular equipment and imaging protocol used in a particular centre. Therefore, the skin dose to patients in other centres may vary considerably from the results in the current study. Also, application of the method of skin dose measurement described in the current study to other types of procedure in this department, or to RF ablation procedures in other centres, must be undertaken with caution. For example, the method of estimating maximum skin dose to a patient using few TLDs would probably not work for PTCA procedures owing to the relatively large range of projections used during these procedures and the difficulty in predicting the most heavily irradiated areas. If TLDs were to be used for PTCAs, a large number of TLDs arranged in an array over the patient's torso would probably be required to provide a good estimate of maximum skin dose. Owing to the labour intensive nature of dose measurement by TLDs, their routine use in this way would be impractical. Another method that has been proposed, and one that may be more appropriate for procedures such as PTCA, is to measure skin dose magnitude and distribution using slow non-screen film positioned at the patient's skin [43, 44]. However, this method was also shown to have its limitation in that the maximum dose that could be accurately measured was 3 Gy [44].
Another disadvantage of using TLDs is that the patient's skin dose is only known some time after the interventional procedure. A method of providing a real-time estimate of patient skin dose is clearly desirable. The importance of real-time dosimetry has been endorsed by Balter [45]: "the rare case in which a burn occurs should be an expected side-effect of a conscious clinical decision. Appropriate real-time dosimetry is the pivot upon which this risk–benefit judgement is made".
If skin dose, as measured by TLDs, shows a strong correlation with dose–area product or fluoroscopy time, then either criterion could be used as a rough guide to the skin dose received during the procedure. Monitoring DAP or fluoroscopy time during each procedure would then allow the operator to be provided with a warning if the patient becomes at risk from suffering deterministic effects. The relationship between skin dose and DAP is shown in Figure 1, the solid line giving the best straight line fit to the data. Similarly, the relationship between skin dose and fluoroscopy time is shown in Figure 2. DAP and skin dose are strongly correlated (n=50, correlation coefficient (r)=0.71, p<0.01). Fluoroscopy time and skin dose are also strongly correlated (n=50, r=0.64, p<0.01). As the correlation coefficient between DAP and skin dose is larger than the coefficient between fluoroscopy time and skin dose in this case, DAP provides the most suitable criterion for providing an estimate of the patient's skin dose during RF ablation. The strong correlation between measured skin dose and DAP additionally provides some assurance that the method used for measuring skin dose was relatively successful and accurate.
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that skin dose can increase at a much faster rate than that described by the best straight line fit to the data. Figure 1 shows the worst case, where skin dose rose most rapidly with increasing DAP. As our aim is to limit the risk of patients suffering deterministic effects, choosing the worst case as the means of estimating skin dose will provide a conservative estimate of the skin dose a patient could receive for a given DAP.
From Figure 1 it can be concluded that as long as the DAP meter reading remains below approximately 100 Gycm2 the patient should receive a skin dose of less than 2 Gy and should not suffer any deterministic effects. If the DAP reaches 300 Gycm2 the patient becomes at risk from suffering main erythema. Although transient and main erythema are not likely to seriously affect patient health, it is important to record and monitor such effects, as the occurrence of erythema suggests certain thresholds have been exceeded and there is a possibility that the threshold for more serious effects may be reached. Patients that have received a dose area product of more than 100 Gycm2 should be advised to report any subsequent skin effects.
It can be concluded from Figure 1 that as long as the DAP meter reading remains below 550 Gycm2, the patient should receive a skin dose of less than 10 Gy and should not suffer any serious deterministic effects. This is only about 25% greater than the maximum DAP recorded during this survey (430 Gycm2), so it is conceivable that a patient could suffer serious deterministic effects from RF ablation treatment in this centre. While the risk is probably small, it is difficult to quantify, and it would be prudent to set 550 Gycm2 as the level of DAP that will trigger further consideration of the risks to the patient. A real-time informed clinical decision to continue with the procedure can then be taken.
There are currently no European DRLs for interventional cardiology examinations. In this department, the three dose levels of 100 Gycm2, 300 Gycm2 and 550 Gycm2 can be used during RF ablation procedures to provide the operator with an indication as to when the patient is at risk of suffering transient erythema, main erythema and serious skin injury, respectively. As these dose levels were derived from a group of patients for a standard RF ablation examination, they can be locally adopted as DRLs for deterministic effects and applied to individual patients. DRL for stochastic effects could be set by locally adopting the mean DAP per RF ablation procedure as the DRL (in this centre, 120 Gycm2 (Table 4)), and monitoring the change in the mean DAP over time. It should be emphasized that because the magnitude and distribution of skin dose is strongly dependent on the particular equipment and imaging protocol used, the DRLs determined for use in this centre for RF ablation procedures should not be applied to RF ablations in other centres, or indeed to other procedures in this centre.
Conclusion
The success rate of the 50 RF ablations carried out in the present study was 96%, which is similar to the success rates of 85% to 96% reported elsewhere [7, 40]. RF ablations result in a certain amount of ionizing radiation exposure to patients undergoing the procedure and to physicians manipulating the electrode catheters and accordingly, risks arise from this use of ionizing radiation. Although generally a successful procedure, the benefit or economical saving derived from RF ablations should not be gained at a net detriment to one's health.
The mean dose received by electrophysiologists for each RF ablation procedure was found to be at least twice the mean dose for the other cardiology procedures carried out in the centre, as could be expected from the protracted nature of the RF ablation procedure. At the workload of an electrophysiologist in this study, of 32 RF ablations and 224 other interventional cardiology procedures per year, the magnitude of the effective dose and equivalent doses to the lens of the eye and to the hands are well below occupational limits. This reflects how good radiation protection practice awareness can be effective in limiting occupational exposure.
The mean effective dose to a patient from a RF ablation was 17 mSv, from which the excess risk of developing a fatal cancer is approximately 0.1%. The maximum effective dose received by a patient was 77 mSv, resulting in an excess risk of developing a fatal cancer of 0.5%. Although these risks must be recognized, they are relatively small compared with the risks associated with alternative approaches to management, including no therapy, antiarrhythmic drug therapy and surgery [46, 47].
The maximum skin dose measured for any patient was 3.2 Gy. This exceeds the minimum dose threshold for transient erythema but is below the 6 Gy and 10 Gy threshold doses for main erythema and moist desquamation. There were no clinical manifestations of skin injury in this study. However, the dose distribution was skewed and occasionally a very difficult procedure might give an anomalously high and dangerous skin dose. Also, the results showed that skin dose can increase at a much faster rate than that described by the mean rate of increase in skin dose. The relationship between measured skin dose and DAP was found to show a strong correlation. Therefore DRLs were devized, in terms of levels of DAP, that will allow the electrophysiologist to be given an indication when patient skin dose approaches certain threshold levels during an examination. This will allow the electrophysiologist to make a real-time, informed, clinical decision as to whether to continue with the procedure. The DRLs of 100 Gycm2, 300 Gycm2 and 550 Gycm2 were locally adopted to provide an indication of the risk of the patient suffering transient erythema, main erythema and moist desquamation, respectively. Patients who have received a DAP of more than 100 Gycm2 will be advised to report any occurrence of adverse skin effects and all reports should be documented. These DRLs will allow the deterministic risk to the patient to be addressed at the time of the RF ablation procedure. In the absence of any national or European recommended DRL for RF ablation procedures, the mean DAP per RF ablation in this centre was also locally adopted as a DRL. This DRL will allow the mean DAP to be monitored over time.
Regulations currently require the establishment of DRLs for each standard radiological investigation. This study has described one method for setting local DRLs to help prevent the occurrence of high skin doses to patients undergoing a standard type of interventional procedure. In addition, a DRL has also been set that helps to limit the stochastic risk to patients. Adopting DRLs in this way helps demonstrate that special attention has been given to the optimization of such high dose procedures. The particular values for the DRLs adopted in this centre must not be applied in other cardiology centres as radiation dose varies with equipment performance, operator experience and departmental protocol, but similar methods could be used to establish their own DRLs.
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Acknowledgments |
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Received for publication March 12, 2001. Revision received August 2, 2001. Accepted for publication September 20, 2001.
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 O. Dragusin, R. Weerasooriya, P. Jais, M. Hocini, J. Ector, Y. Takahashi, M. Haissaguerre, H. Bosmans, and H. Heidbuchel Evaluation of a radiation protection cabin for invasive electrophysiological procedures Eur. Heart J., January 2, 2007; 28(2): 183 - 189. [Abstract] [Full Text] [PDF]
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R E Morrell and A T Rogers Kodak EDR2 film for patient skin dose assessment in cardiac catheterization procedures. Br. J. Radiol., July 1, 2006; 79(943): 603 - 607. [Abstract] [Full Text] [PDF]
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 E. P. Efstathopoulos, D. G. Katritsis, S. Kottou, N. Kalivas, E. Tzanalaridou, E. Giazitzoglou, S. Korovesis, and K. Faulkner Patient and staff radiation dosimetry during cardiac electrophysiology studies and catheter ablation procedures: a comprehensive analysis Europace, June 1, 2006; 8(6): 443 - 448. [Abstract] [Full Text] [PDF]
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 S. Suzuki, S. Furui, H. Kohtake, T. Takeshita, M. Suzuki, K. Kozuma, Y. Yamamoto, and T. Isshiki Radiosensitive Functional Dye: Clinical Application for Estimation of Patient Skin Dose Radiology, May 1, 2006; 239(2): 541 - 546. [Abstract] [Full Text] [PDF]
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 K. Chida, H. Saito, H. Otani, M. Kohzuki, S. Takahashi, S. Yamada, K. Shirato, and M. Zuguchi Relationship between fluoroscopic time, dose-area product, body weight, and maximum radiation skin dose in cardiac interventional procedures. Am. J. Roentgenol., March 1, 2006; 186(3): 774 - 778. [Abstract] [Full Text] [PDF]
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 J. J. Krueger, P. Ewert, S. Yilmaz, D. Gelernter, B. Peters, K. Pietzner, A. Bornstedt, B. Schnackenburg, H. Abdul-Khaliq, E. Fleck, et al. Magnetic Resonance Imaging-Guided Balloon Angioplasty of Coarctation of the Aorta: A Pilot Study Circulation, February 28, 2006; 113(8): 1093 - 1100. [Abstract] [Full Text] [PDF]
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F. W. Schultz and J. Zoetelief Dose conversion coefficients for interventional procedures Radiat Prot Dosimetry, December 1, 2005; 117(1-3): 225 - 230. [Abstract] [Full Text] [PDF]
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O. Dragusin, W. Desmet, H. Heidbuchel, R. Padovani, and H. Bosmans Radiation dose levels during interventional cardiology procedures in a tertiary care hospital Radiat Prot Dosimetry, December 1, 2005; 117(1-3): 231 - 235. [Abstract] [Full Text] [PDF]
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A. Trianni, G. Chizzola, H. Toh, E. Quai, E. Cragnolini, G. Bernardi, A. Proclemer, and R. Padovani Patient skin dosimetry in haemodynamic and electrophysiology interventional cardiology Radiat Prot Dosimetry, December 1, 2005; 117(1-3): 241 - 246. [Abstract] [Full Text] [PDF]
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D G W Onnasch, A Schemm, and H-H Kramer Optimization of radiographic parameters for paediatric cardiac angiography Br. J. Radiol., June 1, 2004; 77(918): 479 - 487. [Abstract] [Full Text] [PDF]
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