Answer to Question #15417 Submitted to "Ask the Experts"
Category: Medical and Dental Equipment and Shielding — Shielding
The following question was answered by an expert in the appropriate field:
We have a radiation safety policy in place at our hospital stating no patient shielding is to be used in the operating room because it would be unhelpful and possibly increase any patient radiation exposure. Presumably this is because most of the exposure comes from internal scatter, the little leakage from the fluoroscope collimator, and the potential for the patient shield to be in the field of view. This would cause increased radiation output from the fluoroscopy machine. We were met with some resistance from a hand surgeon saying he still wants to shield patient thyroid and torso during surgery. He says his medical physicist says our operating room patient shielding policy makes no sense. Is there something we are missing?
The amount of radiation scattered from a patient's extremity during a typical fluoroscopic imaging procedure does not warrant shielding to reduce exposure to the patient's thyroid or torso.
To address this question, let's make certain assumptions about the radiation exposure scenarios presented. In the first scenario, which appears to be the basis for the current hospital policy, it is assumed that that a C-arm fluoroscopic unit is being employed to image a large body part (e.g., head, chest, abdomen, pelvis, etc.). In this scenario, substantial radiation exposure would be necessary to obtain an image useful for the diagnosis and treatment of the patient. However, for the reasons stated in your question, shielding may not be appropriate.
The hand surgeon's comments lead to the second scenario. Typically, medical imaging of an extremity (e.g., hand, ankle, or foot) in the operating room requires only the use of a mini-C-arm fluoroscopic unit. These units produce much less radiation than the unit described above because the patient's extremity is a much thinner body part. This results in substantially less scattered radiation coming from the patient.
In a study of which I was a coauthor, Giordano et al. (2009) monitored for, and recorded radiation scattered from a cadaver ankle specimen during imaging with two different fluoroscopic units: a regular mobile C-arm unit with a 30.5 cm diameter image intensifier and a mini-C-arm unit with a 15.2 cm diameter image intensifier. Dosimeters were placed at various locations within a few inches of the ankle joint specimen. Each C arm unit was energized for 300 sec. No detectable radiation doses (> 10 mrem) were recorded for any of the exposure positions when the mini-C-arm was tested). Only small radiation doses were recorded when the larger C-arm unit was used—0 to 20 mrem, depending on the position of the specimen with regards to the x-ray source.
Both types of fluoroscopy units produce scattered radiation within the patients' imaged body part(s) when energized. However, because the extremity is thin, less radiation is needed to produce a useful image. Because there was negligible radiation detected, the study discussed above supports your hospital's policy of no patient shielding, even for imaging of an extremity.
In addition, see Ask the Experts question 13310 previously posted, on the subject of discontinuing patient shielding as well as a statement on the issue by the National Council on Radiation Protection and Measurements (NCRP).
Thomas Morgan, III, CHP