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Scattered Radiation Level During Videofluoroscopy for Swallowing Study
Clinical Radiology (2002) 57: 614±616 doi:10.1053/crad.2002.0904, available online at http://www.idealibrary.com on
Scattered Radiation Level During Video¯uoroscopy for Swallowing Study C . B . C HA N, L . K. C H A N, H . S. L A M Department of Radiology, Kwong Wah Hospital, Kowloon, Hong Kong Received: 17 May 2001
Revised: 3 August 2001 Accepted: 18 August 2001
AIM: To evaluate the scattered radiation exposure to the surroundings during video¯uoroscopy for swallowing study (VFSS). MATERIALS AND METHODS: Scattered radiation exposure was measured using an ion chamber survey meter for 17 adult patients undergoing video¯uoroscopy for swallowing study. The cumulative dose area product of each case was also recorded. Data were presented as mean + standard deviation. RESULTS: The scattered radiation exposure at a distance of 150 cm from the patient and the dose area product recorded were 149 + 78 mR (range 42±308 mR) and 842 + 544 cGy.cm2 (range 258±2151 cGy.cm2), respectively, for a single study of 18 + 6 minutes. A formula was then derived for estimating the scattered radiation dose to muscle tissue at an arbitrary distance based on the accumulated dose area product. With this formula, the mean scattered radiation dose to naked muscle tissue of the surrounding people at a distance of 30±100 cm from the patient were estimated to be 33.68±3.03 mSv respectively. CONCLUSION: The scattered radiation detriment associated with video¯uoroscopy for swallowing study was well within acceptable levels. Chan, C. B. et al. (2002). Clinical Radiology 57, 614±616. # 2002 The Royal College of Radiologists Key words: scattered radiation, dose area product, video¯uoroscopy for swallowing study.
Video¯uoroscopy for swallowing study (VFSS) is a well recognized diagnostic tool for patients with deglutition disorders [1±3]. Most of the patients who have this examination are weak and therefore need assistance. This assistance is usually provided by the patient's relatives, or occasionally by hospital sta. To our knowledge, there is very little information concerning radiation dose during VFSS [4,5] and virtually no study has been performed to evaluate the scattered radiation to the surroundings, although there is a general concern about signi®cant radiation exposure associated with ¯uoroscopic imaging investigations. The aim of the present study was to investigate the scattered radiation level during VFSS and to relate the scattered radiation exposure to the dose area product (DAP) accumulated during the examination. MATERIALS AND METHODS
From July 2000 to January 2001, the scattered radiation exposure was measured using a highly sensitive (down to 0.01 mR, with 1 R 8.77 mGy in air or 9.56 mGy (approximately equal to 10 mGy for convenience) in muscle Author for correspondence: Dr C. B. Chan, Physicist, Department of Radiology, Kwong Wah Hospital, 25 Waterloo Road, Kowloon, Hong Kong. Fax: (852) 2781 5452; E-mail: [email protected] Guarantors of Study: C. B. Chan, L. K. Chan, H. S. Lam. 0009-9260/02/$35
tissue [6]) ion chamber survey meter (Victoreen 450B, Cleveland, Ohio, U.S.A.) for a total of 17 adult patients undergoing VFSS in our department. The studies were performed with a Philips Diagnost 75 Plus Fluoroscopy unit (Philips Medical Systems, Eindhoven, Netherlands). Each patient was fed by his/her relative with 5 ml and 10 ml of thin barium liquid, thick barium liquid, and congee sequentially using a long spoon. (Some of the above tests might be omitted or repeated depending on the condition and cooperation of the patient). The relative wore lead gloves, a lead collar and a lead apron during the whole examination and was asked to stay behind a lead screen when not feeding the patient. X-ray ¯uoroscopic screening was started and continued during the swallowing process of the patient while the resulting image sequences were videorecorded. The survey meter was placed at a distance of 150 cm from the neck of the patient during the examination and the DAP readings from the DAP meter (Diamentor M2, PTW, Freiburg, Germany) were also recorded. Data were presented as mean + standard deviation.
RESULTS
Figure 1 showed the distribution of duration of VFSS in the present study (18 + 6 minutes). The scattered radiation exposure, after background correction, was 149 + 78 mR # 2002 The Royal College of Radiologists
SCATTERED RADIATION LEVEL DURING VIDEOFLUOROSCOPY FOR SWALLOWING STUDY
615
Fig. 1 ± Distribution of duration of VFSS (n 17).
(range 42±308 mR) while the DAP was found to be 842 + 544 cGy.cm2 (range 258±2151 cGy.cm2). A plot of the scattered radiation exposure versus DAP showed a general increasing trend of scattered radiation exposure with DAP (Fig. 2).
Fig. 2 ± Plot of scattered radiation exposure versus DAP during 17 VFSS. Linear ®t of the data gives y 0.16x, r2 0.60.
DISCUSSION
It is well known that electromagnetic (EM) waves follow the inverse square law. Since the X-ray belongs to the family of EM waves, it also follows the inverse square law. When the X-ray beam from the ¯uoroscopic machine interacts with the patient, part of the X-ray beam will be scattered from the patient to the surroundings ± known as scattered radiation. If the scattered radiation does not encounter further major scattering material before entering the ion chamber of the survey meter, it can also, to a ®rst approximation, be assumed to follow the inverse square law. To validate the above assumption, a Perspex phantom of 30 cm 30 cm 10 cm was irradiated using the same ¯uoroscopic machine in the present study. The scattered radiation exposure was measured during a 60-second irradiation at a distance of 30±150 cm from the phantom. The DAP of each irradiation was also recorded (185 + 2 cGy.cm2). A plot of the log of the scattered radiation exposure per DAP versus the log of the distance from the phantom (Fig. 3) gave a linear ®t of y 2.22x 4.13, r2 0.98. As the slope of the above equation is roughly equal to 2, there exists an inverse square relationship between the scattered radiation exposure per DAP and the distance (30±150 cm) from the subject under investigation. Hence, using the equation in Figure 2 and the inverse square law, we can estimate the cumulative scattered radiation exposure from the DAP during VFSS at arbitrary distance from the neck of the patient as follows:
Equation 1 Scattered radiation exposure at distance d cm (mR) (0.16 DAP (cGy.cm2)) (150/d)2 In the diagnostic X-ray energy region, Gray and Sievert are interchangeable. Therefore, 1 R is approximately equal to 10 mSv. Equation 1 can then be rewritten as:
Fig. 3 ± Plot of log of scattered radiation exposure per DAP versus log of distance from the phantom. Linear ®t of the data gives y 2.22x 4.13, r2 0.98.
Equation 2 Scattered radiation dose to muscle tissue at distance d cm (mSv) (0.16 DAP (cGy.cm2)) (150/d)2/100 It is observed that the variation in DAP in the present study is much greater than that in time of the examination. The latter includes the preparation time, feeding and swallowing time, and resting time of the patient in-between swallowing tests, while the former is, apart from the kV and mA, proportional to the time of irradiation during feeding and swallowing. Normally, the time of irradiation does depend on both the cooperation and the physical condition of the patient but does not depend very much on the time of the examination. An uncooperative and weak patient may need several trials for the same swallowing test and a longer irradiation time for monitoring the feeding and swallowing processes. A cooperative and physically ®t patient in general does not. Hence, there is much greater variation in DAP than that in time of the examination in the present study. A successful VFSS requires contributions from a number of people: radiographers (classi®ed workers) for the preexamination preparation; the radiologist (classi®ed worker) for monitoring the whole process; and the patient's relative (general public) for feeding the patient. Hence, all the above
616
CLINICAL RADIOLOGY
Table 1 ± Mean and worst case scattered radiation dose to muscle tissue at 30, 60, and 100 cm from the neck of the patient during VFSS according to Equation 2 Distance (cm)
Mean dose (mSv)
Worst case dose (mSv)
30 60 100
33.68 8.42 3.03
86.04 21.51 7.74
people may be exposed to scattered radiation during the examination. Normally, the patient's relative will be exposed to the largest amount of scattered radiation. The distances from the neck of the patient to the hand and the body of the patient's relative are about 30 cm and 60 cm respectively during the feeding of the patient. The mean and worst case scattered radiation doses to muscle tissue at dierent distances from the neck of the patient are shown in Table 1. The annual eective dose limit to classi®ed workers is 20 mSv, while to the general public it is 1 mSv. To a ®rst approximation, if we treat the muscle tissue scattered radiation dose to the body as the eective dose, a classi®ed worker can perform 2583 VFSS examinations (using the worst case dose value at 100 cm), while a member of the
public can carry out 46 VFSS examinations (using the worst case dose value at 60 cm) in a year without exceeding the dose limit. Obviously, both ®gures are far above the realistic ®gures. Therefore, it can be concluded that the scattered radiation dose to both the classi®ed worker and to members of the public are well within the limits. In addition, lead aprons are always worn during VFSS; these provide additional protection and further reduce the scattered radiation dose to negligible levels.
REFERENCES 1 Logemann JA. Symptoms and swallowing disorders. In: Logemann JA, ed. Manual for the Video¯uorographic Study of Swallowing. San Diego, USA: College-Hill Press, 1986, 73±113. 2 Jones B, Kramer SS, Donner MW. Dynamic imaging of the pharynx. Gastrointest Radiol 1985;10:213±224. 3 Jones B, Donner MW. Examination of the patient with dysphagia. Radiology 1988;167:319±326. 4 Beck TJ, Gayler BW. Image quality and radiation levels in video¯uoroscopy for swallowing studies: a review. Dysphagia 1990;5: 118±128. 5 Wright RE, Boyd CS, Workman A. Radiation doses to patients during pharyngeal video¯uoroscopy. Dysphagia 1998;13:113±115. 6 Cember H. Introduction to Health Physics. New York, USA: McGraw-Hill, 1996, 177±178.
Scattered Radiation Level During Video¯uoroscopy for Swallowing Study C . B . C HA N, L . K. C H A N, H . S. L A M Department of Radiology, Kwong Wah Hospital, Kowloon, Hong Kong Received: 17 May 2001
Revised: 3 August 2001 Accepted: 18 August 2001
AIM: To evaluate the scattered radiation exposure to the surroundings during video¯uoroscopy for swallowing study (VFSS). MATERIALS AND METHODS: Scattered radiation exposure was measured using an ion chamber survey meter for 17 adult patients undergoing video¯uoroscopy for swallowing study. The cumulative dose area product of each case was also recorded. Data were presented as mean + standard deviation. RESULTS: The scattered radiation exposure at a distance of 150 cm from the patient and the dose area product recorded were 149 + 78 mR (range 42±308 mR) and 842 + 544 cGy.cm2 (range 258±2151 cGy.cm2), respectively, for a single study of 18 + 6 minutes. A formula was then derived for estimating the scattered radiation dose to muscle tissue at an arbitrary distance based on the accumulated dose area product. With this formula, the mean scattered radiation dose to naked muscle tissue of the surrounding people at a distance of 30±100 cm from the patient were estimated to be 33.68±3.03 mSv respectively. CONCLUSION: The scattered radiation detriment associated with video¯uoroscopy for swallowing study was well within acceptable levels. Chan, C. B. et al. (2002). Clinical Radiology 57, 614±616. # 2002 The Royal College of Radiologists Key words: scattered radiation, dose area product, video¯uoroscopy for swallowing study.
Video¯uoroscopy for swallowing study (VFSS) is a well recognized diagnostic tool for patients with deglutition disorders [1±3]. Most of the patients who have this examination are weak and therefore need assistance. This assistance is usually provided by the patient's relatives, or occasionally by hospital sta. To our knowledge, there is very little information concerning radiation dose during VFSS [4,5] and virtually no study has been performed to evaluate the scattered radiation to the surroundings, although there is a general concern about signi®cant radiation exposure associated with ¯uoroscopic imaging investigations. The aim of the present study was to investigate the scattered radiation level during VFSS and to relate the scattered radiation exposure to the dose area product (DAP) accumulated during the examination. MATERIALS AND METHODS
From July 2000 to January 2001, the scattered radiation exposure was measured using a highly sensitive (down to 0.01 mR, with 1 R 8.77 mGy in air or 9.56 mGy (approximately equal to 10 mGy for convenience) in muscle Author for correspondence: Dr C. B. Chan, Physicist, Department of Radiology, Kwong Wah Hospital, 25 Waterloo Road, Kowloon, Hong Kong. Fax: (852) 2781 5452; E-mail: [email protected] Guarantors of Study: C. B. Chan, L. K. Chan, H. S. Lam. 0009-9260/02/$35
tissue [6]) ion chamber survey meter (Victoreen 450B, Cleveland, Ohio, U.S.A.) for a total of 17 adult patients undergoing VFSS in our department. The studies were performed with a Philips Diagnost 75 Plus Fluoroscopy unit (Philips Medical Systems, Eindhoven, Netherlands). Each patient was fed by his/her relative with 5 ml and 10 ml of thin barium liquid, thick barium liquid, and congee sequentially using a long spoon. (Some of the above tests might be omitted or repeated depending on the condition and cooperation of the patient). The relative wore lead gloves, a lead collar and a lead apron during the whole examination and was asked to stay behind a lead screen when not feeding the patient. X-ray ¯uoroscopic screening was started and continued during the swallowing process of the patient while the resulting image sequences were videorecorded. The survey meter was placed at a distance of 150 cm from the neck of the patient during the examination and the DAP readings from the DAP meter (Diamentor M2, PTW, Freiburg, Germany) were also recorded. Data were presented as mean + standard deviation.
RESULTS
Figure 1 showed the distribution of duration of VFSS in the present study (18 + 6 minutes). The scattered radiation exposure, after background correction, was 149 + 78 mR # 2002 The Royal College of Radiologists
SCATTERED RADIATION LEVEL DURING VIDEOFLUOROSCOPY FOR SWALLOWING STUDY
615
Fig. 1 ± Distribution of duration of VFSS (n 17).
(range 42±308 mR) while the DAP was found to be 842 + 544 cGy.cm2 (range 258±2151 cGy.cm2). A plot of the scattered radiation exposure versus DAP showed a general increasing trend of scattered radiation exposure with DAP (Fig. 2).
Fig. 2 ± Plot of scattered radiation exposure versus DAP during 17 VFSS. Linear ®t of the data gives y 0.16x, r2 0.60.
DISCUSSION
It is well known that electromagnetic (EM) waves follow the inverse square law. Since the X-ray belongs to the family of EM waves, it also follows the inverse square law. When the X-ray beam from the ¯uoroscopic machine interacts with the patient, part of the X-ray beam will be scattered from the patient to the surroundings ± known as scattered radiation. If the scattered radiation does not encounter further major scattering material before entering the ion chamber of the survey meter, it can also, to a ®rst approximation, be assumed to follow the inverse square law. To validate the above assumption, a Perspex phantom of 30 cm 30 cm 10 cm was irradiated using the same ¯uoroscopic machine in the present study. The scattered radiation exposure was measured during a 60-second irradiation at a distance of 30±150 cm from the phantom. The DAP of each irradiation was also recorded (185 + 2 cGy.cm2). A plot of the log of the scattered radiation exposure per DAP versus the log of the distance from the phantom (Fig. 3) gave a linear ®t of y 2.22x 4.13, r2 0.98. As the slope of the above equation is roughly equal to 2, there exists an inverse square relationship between the scattered radiation exposure per DAP and the distance (30±150 cm) from the subject under investigation. Hence, using the equation in Figure 2 and the inverse square law, we can estimate the cumulative scattered radiation exposure from the DAP during VFSS at arbitrary distance from the neck of the patient as follows:
Equation 1 Scattered radiation exposure at distance d cm (mR) (0.16 DAP (cGy.cm2)) (150/d)2 In the diagnostic X-ray energy region, Gray and Sievert are interchangeable. Therefore, 1 R is approximately equal to 10 mSv. Equation 1 can then be rewritten as:
Fig. 3 ± Plot of log of scattered radiation exposure per DAP versus log of distance from the phantom. Linear ®t of the data gives y 2.22x 4.13, r2 0.98.
Equation 2 Scattered radiation dose to muscle tissue at distance d cm (mSv) (0.16 DAP (cGy.cm2)) (150/d)2/100 It is observed that the variation in DAP in the present study is much greater than that in time of the examination. The latter includes the preparation time, feeding and swallowing time, and resting time of the patient in-between swallowing tests, while the former is, apart from the kV and mA, proportional to the time of irradiation during feeding and swallowing. Normally, the time of irradiation does depend on both the cooperation and the physical condition of the patient but does not depend very much on the time of the examination. An uncooperative and weak patient may need several trials for the same swallowing test and a longer irradiation time for monitoring the feeding and swallowing processes. A cooperative and physically ®t patient in general does not. Hence, there is much greater variation in DAP than that in time of the examination in the present study. A successful VFSS requires contributions from a number of people: radiographers (classi®ed workers) for the preexamination preparation; the radiologist (classi®ed worker) for monitoring the whole process; and the patient's relative (general public) for feeding the patient. Hence, all the above
616
CLINICAL RADIOLOGY
Table 1 ± Mean and worst case scattered radiation dose to muscle tissue at 30, 60, and 100 cm from the neck of the patient during VFSS according to Equation 2 Distance (cm)
Mean dose (mSv)
Worst case dose (mSv)
30 60 100
33.68 8.42 3.03
86.04 21.51 7.74
people may be exposed to scattered radiation during the examination. Normally, the patient's relative will be exposed to the largest amount of scattered radiation. The distances from the neck of the patient to the hand and the body of the patient's relative are about 30 cm and 60 cm respectively during the feeding of the patient. The mean and worst case scattered radiation doses to muscle tissue at dierent distances from the neck of the patient are shown in Table 1. The annual eective dose limit to classi®ed workers is 20 mSv, while to the general public it is 1 mSv. To a ®rst approximation, if we treat the muscle tissue scattered radiation dose to the body as the eective dose, a classi®ed worker can perform 2583 VFSS examinations (using the worst case dose value at 100 cm), while a member of the
public can carry out 46 VFSS examinations (using the worst case dose value at 60 cm) in a year without exceeding the dose limit. Obviously, both ®gures are far above the realistic ®gures. Therefore, it can be concluded that the scattered radiation dose to both the classi®ed worker and to members of the public are well within the limits. In addition, lead aprons are always worn during VFSS; these provide additional protection and further reduce the scattered radiation dose to negligible levels.
REFERENCES 1 Logemann JA. Symptoms and swallowing disorders. In: Logemann JA, ed. Manual for the Video¯uorographic Study of Swallowing. San Diego, USA: College-Hill Press, 1986, 73±113. 2 Jones B, Kramer SS, Donner MW. Dynamic imaging of the pharynx. Gastrointest Radiol 1985;10:213±224. 3 Jones B, Donner MW. Examination of the patient with dysphagia. Radiology 1988;167:319±326. 4 Beck TJ, Gayler BW. Image quality and radiation levels in video¯uoroscopy for swallowing studies: a review. Dysphagia 1990;5: 118±128. 5 Wright RE, Boyd CS, Workman A. Radiation doses to patients during pharyngeal video¯uoroscopy. Dysphagia 1998;13:113±115. 6 Cember H. Introduction to Health Physics. New York, USA: McGraw-Hill, 1996, 177±178.