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| Fig. 1: A typical shoe-fitting fluoroscope. Source: Wikimedia Commons. |
Fluoroscopy is a technique where a physician or technician images a part of a patient's body using X-rays and a fluorescent screen. [1] The fact that X-rays are ionizing radiation means that modern doctors must carefully weigh the costs and benefits of the procedure, as it represents a significant amount of radiation exposure. [2] This safety concern was not always taken into account, and for many years fluoroscopy was used to fit shoes properly, especially in children. The U.S. Patent for the shoe-fitting fluoroscope was issued in 1927, and it was a common item in shoe stores in the United States through the 1950s. [3] (They remained in use in Britain until the mid-1970s.) Safety regulations were introduced as an informal industry standard in 1946, with at least one state passing similar regulations into law, although there is significant data demonstrating that these regulations were rarely followed. [3,4] The majority of machines surveyed by one study in 1950 had a median radiation output of almost twice the recommended limit, with one machine putting out very nearly 4.5 times more roentgens/minute than the industry limit. [4]
Regulation of shoe-fitting fluoroscopes was for the most part informal, but from 1946 on it was recommended that a person receive no more than 2 roentgens per 5 second exposure (24 R/min) and use a fluoroscope no more than 20 times per year. Despite this standard, most machines were fitted with dials that allowed the time interval to be ranged from 5-45 seconds, with the reportedly most frequent setting at 20 seconds. [3] Although roentgens do not convert exactly into grays, which are the standard unit of radiation absorbance, for soft tissue absorption 1 roentgen is usually approximated to be 0.00876 Gy. [1] Assuming that industry standards were followed precisely and the machine was used for no more than 20 seconds per usage, this works out to a standard limit of 0.0744 Gy per visit, or 1.4883 Gy per year. To put this number in perspective, the LD50 for a single exposure event of ionizing radiation without medical intervention in adults is thought to be 4.5 Gy [5], and the current U.S. occupational annual radiation exposure limit is 0.05 Gy. [6] While it may be difficult to imagine a person getting fitted for shoes 20 times in a single year, machines varied so greatly in their actual radiation output and operation that a total annual absorption of > 1.65 Gy is not entirely infeasible. A 1950 survey of machines put the median output of radiation for these fluoroscopes at 40 R/min, with a mean and maximum of 38.7 and 107 R/min, respectively. [4] A machine set at 40 R/min would give a dose of 0.1240 Gy per 20 second imaging, or up to 2.480 Gy/year. A hypothetical worst-case scenario machine set at 107 R/min for 45 seconds would give a dose of 0.7465 Gy per use, well into the range where it could start giving acute radiation poisoning from a single visit!
The impact of the shoe-fitting fluoroscopes on the health of their users is not really known. While it is known that radiation is a significant carcinogen, there do not appear to have been any long-term studies about how these machines have affected the cancer rates of users or otherwise adversely affected them, and such a study would be very difficult to control properly. Some studies have pointed to specific cancers as the product of shoe-fitting fluoroscopes [3], but given that there were nearly 10,000 machines in the United States alone, and countless customers who tried them but no data to support an extraordinarily high cancer rate among the population the right age to have used them, it appears that the fluoroscopes did not have a significant public health impact. [7] While it is inarguable that radiation can pose a major health risk, it is a testament to the resilience of the human body that people could repeatedly be exposed to such high level of radiation and as a group continue to live without being measurably worse for the wear.
© Sam Birer. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J.T. Bushberg, J.A. Seibert, E.M. Leidholdt, Jr., and J.M. Boone. The Essential Physics of Medical Imaging. Philadelphia: Lippincott Williams & Wilkins, 2002. Print.
[2] K. T. Foley, D. A. Simon, and R. Rampersaud, "Virtual Fluoroscopy. Operative Techniques in Orthopaedics 10, 77 (2000).
[3] M.J. Smullen and D.E. Bertler, "Basal Cell Carcinoma of the Sole: Possible Association with the Shoe-Fitting Fluoroscope. ," Wisconsin Medical Journal 106, 5 (2007).
[4] K. L. Lewis and P.E. Kaplan, "The Shoe-Fitting Fluoroscope as a Radiation Hazard. California Medicine 72, 1 (1950).
[5] R.H. Mole,"The LD50 for Uniform Low LET Irradiation of Man. ," The British Journal of Radiology 57, 677 (1983).
[6] M.V. Marx, L. Niklason, and E.A. Mauger,"Occupational Radiation Exposure to Interventional Radiologists: A Prospective Study. ," The Journal of Vascular and Interventional Radiology 3, 4 (1992).
[7] "X-Ray Shoe Fitting Machine. ," Wisconsin Historical Society Curator's Favorites, 2006.
