ObjectMinimally invasive transforaminal lumbar interbody fusion (TLIF) is an increasingly popular procedure. The technique involves use of fluoroscopy to assist with pedicle screw (PS) placement. The potential exists for both the surgeon and the patient to become exposed to significant amounts of radiation. The authors undertook this study to quantify the radiation dose to the surgeon and patient during minimally invasive TLIF.MethodsThe authors undertook a prospective study of 24 consecutive patients who underwent minimally invasive TLIF. All surgeries were performed by the senior author (R.K.B.), who used techniques previously described. The surgeon wore a radiation monitor under an apron-style lead shield at waist level, at an unshielded collar location, and as a sterile ring badge containing a thermoluminescent dosimeter on the dominant (right) hand ring finger. Dosimeter readings were obtained for each case. A total of 33 spinal levels were treated in 24 patients. All treated levels were between L3–4 and L5–S1. In all cases of 1-level disease, 4 PSs were placed, and in all cases of 2-level disease, 6 screws were placed.Results. Mean fluoroscopy time was 1.69 minutes per case (range 3.73–0.82 minutes). Mean exposure per case to the surgeon on his dominant hand was 76 mRem, at the waist under a lead apron was 27 mRem, and at an unprotected thyroid level was 32 mRem. Mean exposure to the patient's skin was 59.5 mGy (range 8.3–252 mGy) in the posteroanterior plane and 78.8 mGy (range 6.3–269.5 mGy) in the lateral plane.ConclusionsTo the authors' knowledge, this is the first study of radiation exposure to the surgeon or patient in minimally invasive TLIF. Patient exposures were low and compare favorably with exposures involving other common interventional fluoroscopically guided procedures. Surgeon exposures are limited but require careful monitoring. Annual dose limits could be exceeded if a large number of these and other fluoroscopically guided procedures were performed.
Traditionally, the absorption properties of protective aprons used in diagnostic radiology have been specified in units of lead equivalent thickness. This is appropriate and accurate when lead is the only high-atomic-numbered component in the apron. In an attempt to manufacture light-weight protective apparel, however, some manufacturers have included other elements with k absorption edges in the energy range of interest, to provide equivalent absorption properties with less weight. With these other high-atomic-numbered elements added, the lead equivalence of the apparel becomes a function of the photon energy. This must be recognized and specified by the supplier, because lead apparel is used in environments other than diagnostic radiology, where the shielding benefits may be substantially less than expected when specifications are based on the diagnostic x-ray energy range.
Each section of the Alderson Rando phantom contains a tissue-equivalent plastic coating layer approximately 2 mm thick, applied to both faces. This compensates for material removed in the sawing process. Conventional use of thermoluminescent dosimeters positions them totally or partially within the coating layer. Analysis shows that, in the lung region, dosimeters placed in this layer received a dose averaging 39% lower than those placed at midsection. Where bony structures interfere, some dosimeters in the coating layer received an 18% higher dose than those at midsection. Therefore, positioning dosimeters at the center of a section is recommended.
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