Patient body mass index significantly impacts surgeon radiation dose

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Minimally invasive procedures utilising fluoroscopy are becoming increasingly popular. Little research has been performed, however, on the impact of patient body mass index on radiation dosage. A prospective study from Keio University School of Medicine (Tokyo, Japan) has found that a patient’s body mass impact can significantly affect the radiation dose experienced by surgeons during minimally invasive transforaminal interbody fusion procedures.

Lead author of the study, Ken Ishii, explained the importance of investigating the relationship between patient body mass index and radiation exposure to surgeons. “It is often difficult to get high quality bone images in obese patients, because of thickness of soft tissues such as muscle and fat,” he told Spinal News International.  Higher radiation doses are therefore required to achieve adequate C-arm images. “Prior to this study, we suspected that the direct radiation exposure to the obese patient maybe high compare with the normal-weight patient,” Ishii said. “Although it is known that positive correlation exists between direct radiation exposure and scatter radiation exposure, we were not sure whether we could detect this phenomenon and this result before performing the clinical study.”

The study—which was presented at Spineweek (Singapore; 16-20 May)—enrolled twenty consecutive patients undergoing single-level minimally invasive transforaminal interbody fusion. Of the twenty patients, four were considered to be overweight (body mass index ≥25, mean=27.2kg/m2), while 16 were considered to be of normal weight (body mass index >25, mean=23.3kg/m2). Equipped with thermoluminescent dosimeters at the thyroid, chest and genitals, operative and assisting surgeons performed the single level procedures at L2-3 (n=1), L3-4 (n=1), L4-5 (n=14) and L5-S1 (n=4). Surgeons also wore a thermoluminescent dosimeter under a lead apron on the chest, as well as sterile ring dosimeters on the right middle finger. Other measures, including estimate blood loss, fluoroscopic time and surgical time were recorded.

The mean radiation dosage was found to be significantly higher for the operating surgeon at the chest in patients that were overweight, at 0.14mSv versus 0.08mSv for normal-weight patients (p=0.0002). Assisting surgeons experienced a significantly higher dosage to the genitals in the case of overweight patients (0.12mSv) in comparison to normal-weight patients (0.06mSv, p=0.039). No significant differences were found between the groups in the case of surgical time, estimated blood loss, fluoroscopic exposure time, or radiation dosage at other point on the body.

The authors concluded that body mass index significantly affected the radiation dose experienced by surgeons. Speculating on the cause of their results, they wrote, “higher scatter radiation caused by higher radiation outputs and larger body surface areas might increase the surgeons’ radiation doses.” Future research will be concentrated on exploring radiation dosage associated with other spinal procedures. Ishii told Spinal News International, “We are planning to measure the radiation exposure during lateral access surgery such as extreme lateral interbody fusion.”

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