AJR: Dose equation for steroid injections merits careful consideration

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The effective radiation dose for a CT fluoroscopy (CTF) is about half of conventional fluoroscopy when guiding epidural steroid injections (ESI); however, the overall radiation dose is substantially higher when a full lumbar planning CT scan is performed as part of the CT-guided procedure, according to a study published in the October edition of the American Journal of Roentgenology.

The results of the study, conducted by Jenny K. Hoang, MBBS, and colleagues from Duke University Medical Center, in Durham, N.C., showed the radiation dose of conventional fluoroscopy was 0.85 mSv compared with 0.45 mSv for CTF when guiding ESI. When the procedure includes a planning lumbar spine CT scan, though, the total dose increased to 3.35 mSv.

“Although CT provides better visualization of the epidural space, conventional fluoroscopy may be favored over CTF for lumbar ESI procedures because of concern about higher radiation exposure resulting from CT techniques,” wrote the authors.

The researchers said physicians may hesitate to use CTF because of concerns about radiation dose, but because CTF takes less time than conventional fluoroscopy, the absorbed radiation dose can be much lower. For CTF, the average time for an ESI was 4.7 seconds compared with 37 seconds for conventional fluoroscopy. This average time doesn’t take into account the main source of radiation dose from CT-guided ESI, however, which is the preliminary planning CT.

Hoang et al acknowledged that fluoroscopy times for spine procedures can vary widely based on operator experience and other factors. The researchers emphasized the results of the study are based on protocols from their institution. They also noted that the maximum z-axis possible for the planning CT could be reduced in some cases if the intervertebral level affected has been identified with prior diagnostic imaging.

CTF may still be chosen over conventional fluoroscopy since it can better show soft tissue and requires less iodinated contrast media, but the researchers advised taking precautionary steps.

“Radiologists performing CTF-guided lumbar spine procedures should carefully consider techniques to reduce radiation dose for the preliminary lumbar spine CT scan by reducing the z-axis length and reducing the tube output,” wrote the authors.