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British Journal of Radiology (2006) 79, 603-607
© 2006 British Institute of Radiology
doi: 10.1259/bjr/78359708
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Full paper

Kodak EDR2 film for patient skin dose assessment in cardiac catheterization procedures

R E Morrell, MSc, MIPEM and A T Rogers, MSc, MIPEM

Medical Physics Directorate, Nottingham City Hospital NHS Trust, Hucknall Road, Nottingham NG5 1PB, UK


   Abstract
Top
 Abstract
Introduction
 Method
 Results
 Discussion
 Conclusion
 References
 
Patient skin doses were measured using Kodak EDR2 film for 20 coronary angiography (CA) and 32 percutaneous transluminal coronary angioplasty (PTCA) procedures. For CA, all skin doses were well below 1 Gy. However, 23% of PTCA patients received skin doses of 1 Gy or more. Dose–area product (DAP) was also recorded and was found to be an inadequate indicator of maximum skin dose. Practical compliance with ICRP recommendations requires a robust method for skin dosimetry that is more accurate than DAP and is applicable over a wider dose range than EDR2 film.


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 Conclusion
 References
 
Cardiac catheterization procedures can involve prolonged fluoroscopic imaging and large numbers of acquired images. As a result, patient skin doses may approach or exceed the threshold for deterministic skin effects [1–6].

The US Food and Drug Administration [7], and more recently the International Commission on Radiological Protection (ICRP), have published guidelines for dose minimization and for recording skin doses to patients who are suspected to be at risk. ICRP Report 85 [8] recommends that the magnitude and position of the maximum skin dose should be recorded in the patient's notes if it exceeds 1 Gy for procedures that are likely to be repeated, or 3 Gy for all procedures. Patients who are considered to be at risk should receive appropriate information and clinical follow-up.

Implementation of these guidelines requires a robust method for assessment of patient skin doses. Modern cardiac X-ray units are fitted with dose–area product (DAP) meters, which indicate the total amount of radiation incident on the patient's skin. However, there is no simple relationship between DAP and maximum skin dose. The dose distribution depends on which imaging projections are used, and for what proportion of the procedure. This can vary greatly from one patient to the next depending on operator preference, the anatomy of the patient's disease, and the complexity of the procedure. Whilst some authors have proposed DAP values to alert the operator to the potential for deterministic effects [9–12], others have reported poor correlations between DAP and maximum skin dose [13–15].

Slow radiographic film can be used to record a map of the skin dose distribution over a large area. As long as the film is not saturated, absolute dose measurements can be made directly from the film and any regions of high dose can be easily identified. Of the films that are compatible with standard radiology processors, the wide latitude films developed for portal imaging and quality control applications in radiotherapy are responsive to the highest radiation doses, and are thus most suitable for dosimetry in high dose diagnostic and interventional procedures [13, 16–18].

The dosemeter selected for this study was Kodak EDR2 film (Eastman Kodak Company, Rochester, NY), which currently has the widest available dose range. Guibelalde et al [19] have successfully used it for skin dosimetry during interventional cardiology procedures. They reported its saturation point at 1.4 Gy, and found saturation to occur in about 1% of cases.

The performance of the film has been characterized in detail, as described in a previous paper by the authors [20]. It is available in 35 cm x 43 cm sheets, which are large enough to capture most of the radiation fields on the patient's back. It is pre-wrapped in light-proof paper, ready for use. It can be processed in a standard radiology processor using non-glutaraldehyde chemicals.

The purpose of the study was to determine typical skin doses for patients undergoing coronary angiography (CA) and percutaneous transluminal coronary angioplasty (PTCA) in our cardiac catheterization laboratory, and to estimate the percentage of patients receiving doses of 1 Gy or more. The film measurements were compared with DAP to determine whether DAP could be used as a predictor of maximum skin dose.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 Conclusion
 References
 
The film was previously calibrated over the range of exposure conditions typically encountered in our cardiac catheterization laboratory [20]. Its response was characterized across the dose range 20–1000 mGy. The effects of beam energy and filtration, field size, exposure rate, film batch and processing conditions were quantified. The relationship between dose (D) and optical density (OD) was found to be:


Formula 001

The constant {alpha} had a value of 0.0027 mGy–1 when a 20 cm polymethylmethacrylate (PMMA) phantom was used to simulate the backscatter from a patient and with the processing conditions used in our department. The mean optical density of unexposed film (ODmin) was 0.21, whilst the mean density of fully exposed film (ODmax) was 3.92. The film saturated at around 1 Gy. The uncertainty in dose per optical density was estimated to be –29 mGy to +62 mGy at a fixed dose of 160 mGy, across the full range of exposure and processing conditions employed. At other dose levels, this interval was assumed to scale linearly with the gradient of the calibration curve, given by:


Formula 002

Skin doses were measured for 20 CA and 32 PTCA procedures, performed on an Integris H5000F C-arm imaging unit (Philips Medical Systems, Best, Netherlands). The imaging equipment was subject to monthly and annual quality control checks, as recommended by the Institute of Physics and Engineering in Medicine [21]. Patients were selected sequentially, and the study included only those procedures performed by our in-house consultant cardiologists and the registrars working under their supervision. Fluoroscopy was performed using the "low continuous" factory setting, which has a nominal input dose rate at the detector of 740 nGy s–1 and employs 0.4 mm copper filtration. All acquisition runs were performed on the "12.5 FPS Coronary" setting, which has a nominal detector input dose rate of 870 nGy s–1 and has no copper filter.

Before commencing each procedure, a sheet of 35 cm x 43 cm EDR2 film was positioned on the imaging table, underneath the mattress. The dotted rectangle in Figure 1Go demonstrates the position and orientation of the film. Its long axis was perpendicular to the long axis of the table, and its top edge was approximately level with the patient's shoulders. Each film was labelled to indicate which side was face-up, and which edge was closest to the patient's head. Following exposure, a pinhole was made in the corner of the film packet corresponding to the patient's left shoulder, to identify the orientation of the processed film.


Figure 1
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  		Figure 1. Film position and orientation.

 
All films were stored in their packets overnight before processing, since the response of EDR2 film takes some time to stabilize following exposure [20, 22]. They were then processed in a Kodak X-OMAT M6B processor (Eastman Kodak Company, Rochester, NY), with Photosol developer and fixer (Photosol Limited, Basildon, UK). The maximum optical density of each film was determined manually, using a Pehamed Densoquick 2 densitometer (Pehamed, Sulzbach, Germany).

The DAP for each procedure was measured using an integral PTW-DIAMENTOR-M1 DAP meter (PTW-FREIBURG, Freiburg, Germany). This had previously been calibrated over the same range of exposure conditions as the film. The uncertainty in its response was estimated at ±13%. The Pearson correlation coefficient between DAP and peak skin dose was calculated for each procedure type, for those procedures where no film saturation occurred. The significance of the correlations was determined using Student's t-test.


   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 Conclusion
 References
 
Figure 2Go shows a dosimetry film from a PTCA procedure, viewed as if looking at the patient's back. The patient's left shoulder is indicated by the black spot in the top left-hand corner of the image. The region of maximum dose can be readily identified by the darkest patch, in the top right-hand quadrant.


Figure 2
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  		Figure 2. A dosimetry film from a coronary angioplasty, viewed as if looking at the patient's back. The black spot in the top left-hand corner indicates the patient's left shoulder.

 
One film from each procedure type showed abnormally large numbers of radiation fields, with extensive areas of film saturation. Since the DAP from these examinations was not particularly high, it seemed likely that these films had been left on the imaging table for more than one procedure. Both were excluded from the data analysis.

Figure 3Go shows the distribution of maximum skin doses for coronary angiography and angioplasty procedures. Skin doses for the angiograms were all less than 600 mGy. Seven films from angioplasty procedures were saturated in at least one region, implying a skin dose of 1 Gy or more.


Figure 3
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  		Figure 3. Maximum skin doses for coronary angiography(CA) and percutaneous transluminal angioplasty (PTCA) procedures.

 
GoFigures 4 and 5Go are scatter plots of maximum skin dose against DAP for the two procedure types, for films that demonstrated no saturation. A linear trend has been fitted to each. The error bars indicate the expected uncertainties in the measurements, as described in the method.


Figure 4
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  		Figure 4. Maximum skin dose versus dose–area product (DAP), for coronary angiography (CA).

 

Figure 5
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  		Figure 5. Maximum skin dose versus dose–area product (DAP), for coronary angioplasty (PTCA) procedures for which no film saturation occurred.

 
The Pearson correlation coefficients between maximum skin dose and DAP were 0.76 for coronary angiography, and 0.61 for coronary angioplasty. These correlations were both significant (p = 0.05). However, GoFigures 4 and 5Go show that some of the points deviate considerably from the trend lines.


   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
Conclusion
 References
 
For coronary angiography, all skin doses were well below 1 Gy. This is in agreement with other published studies using thermoluminescence dosimetry or film [13–15, 23, 24]. The mean peak skin dose was 195 mGy, with a range from 70 mGy to 520 mGy. Patients undergoing these diagnostic investigations are unlikely to receive doses sufficient to cause deterministic effects.

For coronary angioplasty, 23% of patients received skin doses of 1 Gy or more, sufficient to saturate the film. It must be assumed that a similar proportion of our patients approach or exceed this level in routine clinical practice. Since it is fairly common for patients to undergo more than one procedure, the dose to each of these patients should be assessed and recorded.

Thermoluminescence dosimetry studies by Van de Putte et al, Waite and Fitzgerald, and Verdun et al all found some skin doses approaching or exceeding 1 Gy, for PTCA patients [14, 15, 24]. The increased incidence of film saturation compared with that reported by Guibelalde et al may be at least partly explained by our lower film saturation point of 1 Gy. Even if this is increased to 1.5 Gy using a dedicated processor as Guibelalde did, the film still cannot measure doses up to the 2 Gy threshold for deterministic effects.

Given the large proportion of patients receiving skin doses of at least 1 Gy, it seems likely that some of them exceed the 2 Gy threshold for deterministic effects [25]. These patients should be monitored for skin effects, and informed about potential symptoms and appropriate action to take should any skin changes occur.

The study clearly identifies a need for routine assessment of patient skin doses for coronary angioplasty procedures in our cardiac catheterization laboratory.

EDR2 film identifies those patients whose doses may exceed 1 Gy, and who may therefore be at risk of deterministic skin effects. However, since this film saturates at 1 Gy, it cannot be used to assess these higher doses. It is labour-intensive as a dosimetry method, because each film must be individually positioned and labelled, processed and analysed to determine the maximum dose. A further limitation of film dosimetry is that contributions from lateral and very wide oblique views are not measured.

DAP was found to be a poor indicator of maximum skin dose, because clinical practice varies so much from one procedure to the next. Although there was a significant correlation between DAP and maximum skin dose for both procedure types, it is evident from GoFigures 4 and 5Go that DAP alone cannot not reliably predict high skin doses.

Alternative dosemeters used in cardiac catheterization procedures include thermoluminescent dosemeters and scintillation detectors [14, 15, 24, 26]. A major disadvantage of such detectors is their small area. The location of the maximum skin dose is not usually known in advance and, if there is no detector at this exact location, skin dose can be grossly underestimated. There is now a growing range of "Gafchromic" films, produced by International Speciality Products (Wayne, New Jersey). These are designed specifically for patient dosimetry applications, have higher dose ranges than EDR2 film, and do not require any processing. At present however, they are prohibitively expensive for routine dosimetric use.

A potential solution would be a mathematical model, to calculate skin dose distribution from the exposure parameters recorded in the DICOM image files for each individual acquisition run. As well as enabling assessment of doses above the film's saturation point, this would require less staff involvement than film dosimetry. The model could be applied routinely for all patients or run for individual patients whose DAP exceeds a certain trigger level.


   Conclusion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
References
 
Skin doses in our cardiac catheterization laboratory are unlikely to exceed 1 Gy for CA. However, around 23% of our patients receive maximum skin doses of at least 1 Gy during PTCA procedures. DAP is not an adequate indicator of patient skin dose. Practical compliance with ICRP recommendations requires a method for routine assessment of skin doses that is more accurate than DAP, and is applicable over a wider dose range than EDR2 film. This may be achievable by means of a mathematical model.


   Acknowledgments
 
We would like to thank our cardiologists for agreeing to participate in this study, and our catheterization laboratory radiographers and nurses for their invaluable assistance with data collection. We are grateful to Prof. Alan Perkins for helpful discussions.

Received for publication April 22, 2005. Revision received October 7, 2005. Accepted for publication October 25, 2005.


   References
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
 References
 

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This Article
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