British Journal of Radiology (2004) 77, 654-656
© 2004 British Institute of Radiology
doi: 10.1259/bjr/22832251
Patient and operator dose during fluoroscopic examination of swallow mechanism
M T Crawley, MSc, MIPEM
1
P Savage, FRCS, FRCR
1 and
F Oakley, BSc, MRCSLT
2
1 Radiology Department and 2 Speech and Language Therapy Department, Stoke Mandeville Hospital, Mandeville Road, Aylesbury, Buckinghamshire HP21 8AL, UK
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Abstract
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Dose–area product (DAP) measurements were made for 21 patients undergoing a modified barium swallow. The procedures were performed by a radiologist and speech and language therapist, to characterize swallowing disorders in patients with head or spinal injury, stroke, other neurological conditions or simple globus symptoms, in order to inform feeding strategies. The DAP values were used to estimate effective dose to the patient, in order to provide a measure of the radiation risk associated with the procedure. Whole body doses to operators, together with equivalent doses to extremities and eyes were also measured to inform the employer's risk assessment. Median DAP for the series was 3.5 (3.1–5.2) Gycm2 with a corresponding effective dose to the patient of 0.85 (0.76–1.3) mSv, and a low associated risk, mainly of cancer induction, of about 1 in 16 000. The organ receiving the greatest dose was the thyroid, with a calculated median equivalent dose of 13.9 (12.3–20.7) mSv. Median screening time was 3.7 (2.5–4.3) min. Mean operator doses were 0.5 mSv equivalent dose (eyes), 0.9 mSv (extremities), and less than 0.3 mSv whole body dose. Extrapolating for an annual workload of 50 patients per year, this work will lead to annual operator doses of less than 0.6 mSv whole body dose, and approximately 1 mSv equivalent dose (eyes) and 1.8 mSv (extremities), against corresponding legal dose limits of 20 mSv, 150 mSv and 500 mSv, respectively.
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Introduction
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It has been shown that contrast barium studies can be useful in characterizing swallowing abnormalities affecting patients with dysphagias in the oral and pharyngeal stages of the swallow [1–3]. Oral dysphagias include impairment in preparing the bolus for the swallow (difficulty with mastication), delayed triggering of the swallow, incomplete swallow (residue left in the oral cavity after the swallow), and premature entry of the bolus into the pharynx (with possible entry into the unprotected airway). Disorders in the pharyngeal stage of the swallow include pooling in the valleculae or pyriform sinuses (with consequent risk of aspiration), penetration into the laryngeal vestibule with or without actual aspiration, aspiration, reduced or absent laryngeal elevation (preventing the cricopharyngeal sphincter from opening), and delayed or absent cricopharyngeal opening.
There is a legal requirement on persons conducting medical radiation exposures to monitor radiation dose to the patient and to establish local diagnostic reference levels for such exposures [4]. Likewise there is a legal requirement on employers to monitor radiation doses to staff working with radiation, and to perform a suitable and adequate radiation risk assessment, for which a knowledge of typical doses and dose rates is required [5]. In the present study, radiation doses to patients and operators resulting from fluoroscopic swallow examinations were recorded for 21 patients, with the aim of assessing the associated radiation risk to patients and staff and establishing a local diagnostic reference level in terms of dose–area product (DAP) for the procedure. Fluoroscopic exposure times were also recorded.
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Method
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21 patients with oral and/or pharyngeal dysphagia underwent a modified barium swallow. The patients were a random group, the majority of whom suffered from stroke, head or spinal injury, other neurological conditions or simple globus symptoms. All examinations were performed on an overcouch tube fluoroscopic screening unit (Siemens Uroskop C2, Siemens Aktiellangenschdat, Germany), and all were performed by the same consultant radiologist and speech and language therapist working together, in close proximity to the patient.
The technique used in the modified barium swallow differs from that used in the more usual barium swallow in that patients are given a mixture of pureed food with barium, in various consistencies, to swallow. Patients are also assessed while trying different swallowing techniques such as: effortful swallow, chin tuck, head turning, supraglottic swallow (breath-hold before swallow), and Mendelssohn manoeuvre (voluntary control of laryngeal rise). Time is also spent assessing the patient with boluses of different sizes and at varied rates of eating and drinking. The purpose of investigating the various techniques and food consistencies is to determine whether penetration or aspiration can be prevented and the patient could continue or resume oral intake.
The patients were assessed in a seated posture, on a chair, wheelchair or trolley, or else standing. The X-ray equipment was rotated to give a lateral projection in the normal non-magnified image field mode, nominally 27 cm diameter. The equipment was operated in automatic dose control mode, and fluoroscopic image sequences were recorded on video, with no requirement for conventional or digital spot images. The area covered by the irradiated field was assessed from video images, and typically covered the hard palate at the anterior and superior limits, the posterior spinal processes, and was limited by the density of the shoulders at the inferior margin.
The X-ray tube was equipped with an integral DAP meter (PTW, Freiburg, Germany), which was calibrated according to published methods [6]. All equipment was subject to routine quality control throughout the period of data collection with fluoroscopic dose rates and image quality remaining within defined parameters.
Patient radiation doses were quantified by recording the total DAP for each examination. Median, first and third quartiles of the resultant DAP distribution were calculated. Effective dose was then estimated using commercially available software, ODS60 [7]. The quantity effective dose has been defined by the International Commission for Radiological Protection (ICRP), as the sum of the weighted equivalent doses to defined organs, and provides a useful measure of the radiation risk [8]. The software required entrance skin dose, without backscatter, as an input parameter, and then utilized depth dose data in an anthropomorphic phantom to determine the individual organ absorbed doses, from which equivalent doses to organs and thence the effective dose was calculated. The software enabled close matching of the simulated fluoroscopic projection to that used in clinical practice, and employed a patient size-and-sex adjustable phantom. However, to reflect the patient population examined in the present study, the phantom selected was a 70 kg adult. Entrance skin dose was determined by dividing the median DAP value by the area irradiated at the patient entrance surface. As there was no scope for the use of collimation in these particular studies, with the required anatomical detail filling the image field, the area of the irradiated field at the patient entrance surface was approximately 170 cm2, and was determined by making geometric corrections to the area of the nominal intensifier input field. Fluoroscopic screening times were also recorded.
Operator doses were recorded using thermoluminescent dosemeters worn on the finger of the right hand (both operators being right-handed), and on the forehead, to provide dose estimates for extremities and eyes, respectively. A whole body dosemeter was also worn on the lower trunk under a protective lead apron. Whole body dosemeters were changed three times during the 6 months of data collection, in line with the usual dose monitoring practice for whole body monitoring in this department. In the case of the radiologist, the accrued dose on the whole body dosemeter included that resulting from other radiological work. For both radiologist and speech therapist, the under-apron dose was assumed to provide a reasonably close approximation to effective dose, neglecting any contributions from doses to organs and tissues not covered by the apron, in line with usual practice.
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Results
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Median DAP for the series of 21 patients was 3.5 (3.1–5.2) Gycm2 with a corresponding effective dose to the patient of 0.85 (0.76–1.3) mSv. The organ receiving the greatest dose was the thyroid, with a calculated median equivalent dose of 13.9 (12.3–20.7) mSv. Median screening time was 3.7 (2.5–4.3) min.
Mean operator doses were 0.5 mSv equivalent dose (eyes), and 0.9 mSv equivalent dose (hands). Whole body doses, as reflected by the under-apron dosemeter, were less than 0.3 mSv; being below the reporting threshold of 0.1 mSv for each of the three consecutive dosemeters worn during the period spanned by the study. Extrapolating to an annual workload of 50 patients per year, this work will result in annual operator doses of less than 0.6 mSv (whole body), 1 mSv (eyes), and 1.8 mSv (extremities), against legal dose limits of 20 mSv, 150 mSv and 500 mSv, respectively [5].
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Discussion
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Patient effective dose provides a measure of the overall risk to the patient from radiation exposure. ICRP publishes data on radiation doses and risks and currently proposes a probability coefficient for stochastic effects in the whole population from radiation exposure, of 7.3 x 10–2 Sv–1, corresponding to a risk of about 1 in 14 000 per mSv effective dose [8]. The risk incorporates all deleterious effects, the main risk being that of cancer induction in the exposed individual, though the risk also includes genetic effects in descendants. The overall risk associated with a modified swallow examination, with an effective dose of 0.85 mSv at the median DAP value, is therefore shown to be low, at approximately 1 in 16 000.
Based on dose data from national surveys, the National Radiological Protection Board (NRPB) quote a median DAP value of 6.6–8.3 Gycm2 for a standard barium swallow, depending on whether conventional or digital spot imaging is used, and a median screening time of 104 s [9]. This DAP value is approximately twice the median recorded for the modified swallow, therefore the patient effective dose from the modified swallow is approximately half that from the standard barium swallow, despite the longer screening time. This is mainly due to the absence of a requirement for spot images in the modified swallow. The highest contribution to the effective dose arises from the equivalent dose to the thyroid, of 12–21 mSv.
Whilst some of the patients suffered from clinical globus symptoms and were found to have a low risk of serious pathology, a substantial number of patients had a serious newly identified problem, including those with cerebrovascular accidents, high spinal lesions or neurodegenerative disorders. These patients have a high risk of aspiration and we have shown that a modified barium swallow examination informs the crucial decision as to the most appropriate method of feeding, and the most appropriate consistency of food and drink. This can be achieved at low risk to both patient and operator.
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Footnotes
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Address correspondence to M T Crawley, Department of Medical Physics and Clinical Engineering, Churchill Hospital, Old Road, Headington, Oxford OX3 7LJ, UK. 
Received for publication June 23, 2003.
Revision received December 4, 2003.
Accepted for publication February 3, 2004.
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References
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- Martin-Harris B, Logemann JA, McMahon S, Schleicher M, Sandidge J. Clinical utility of the modified barium swallow. Dysphagia 2000;15:136–41.[Medline]
- Logemann JA. Role of the modified barium swallow in management of patients with dysphagia. Otolaryngol Head Neck Surg 1997;116:335–8.[CrossRef][Medline]
- Logemann J. Evaluation and treatment of swallowing disorders. Boston, MA: College Hill Press, 1983.
- Ionising Radiation (Medical Exposure) Regulations 2000 SI 2000/1059. London: HMSO, 2000.
- Ionising Radiations Regulations 1999 SI 1999/3232. London: HMSO, 1999.
- Dosimetry Working Party of the Institute of Physical Sciences in Medicine. National protocol for patient dose measurements in diagnostic radiology. Chilton: NRPB, 1992.
- ODS 60 Organ Doses Calculation Software, RADOS Technology Ltd, Newbury, Berkshire, UK.
- International Commission on Radiological Protection. 1990 Recommendations of the ICRP, ICRP Publication 60. Ann ICRP 1991:21.
- Hart D, Hillier MC, Wall BF. Doses to patients from medical X-ray examinations in the UK – 2000 Review. NRPB –W14. Didcot, UK: NRPB, 2002.
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Abstract
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