“Select the best measure field that could minimize the area of Onyx cast in the field to prevent burning of the image field,” senior author advises.
The successive Onyx embolization procedures required to treat arteriovenous malformations (AVMs) of the brain are accompanied by rising amounts of fluoroscopic radiation between the initial embolization session and the final session, new research shows. The study, published online recently in the Journal of NeuroInterventional Surgery, shows the increased radiation dose appears to be a result of the presence of radiopaque Onyx cast from previous injections in the multistage process.
“Preventing the burning effect in fluoroscopic images through the proper setting of the automatic exposure control [AEC] system, in addition to basic radiological procedural principles, such as active use of collimation and limited application of magnification, may help reduce the inadvertent radiation exposure burden,” senior author Deok Hee Lee, MD (Asan Medical Center, Seoul, Korea), told Neurovascular Exchange via email.
Lee added that it would also be helpful if the manufacturer could install more effective measuring field options in the AEC system.
Addressing a Known Problem
In recent years the indications for endovascular procedures and the use of multiple procedures in certain clinical situations has expanded, according to Lee. Because Onyx embolization usually requires a relatively long injection duration and an inevitably long fluoroscopic time, issues with radiation dose have arisen.
To try to reduce this radiation burden, Lee along with lead author Jae Jon Sheen, MD (Asan Medical Center), and colleagues decreased the fluoroscopic pulse rate from 7.5 to 4 during Onyx injection. However, they still found “that the radiation dose tended to be higher in successive embolization procedures then in the first procedure and that most of the dosage difference was due to the increased fluoroscopic dose,” Lee said.
Because of this, the researchers hypothesized that presence of previously injected Onyx cast caused burning effect of the fluoroscopic images on successive procedures. Presence of attenuating material can increase the dose production setting to maintain the image brightness controlled by AEC.
Lee and colleagues conducted a retrospective study of 18 patients who underwent multistage Onyx embolization for brain AVMs, comparing the frontal and lateral fluoroscopic dose rates of the final embolization session with the initial session.
Measures showed significantly different fluoroscopic dose rates between the two procedures. For the frontal plane, the dose-area product was 0.668 Gy x cm2 per min at the initial session compared with 0.848 Gy x cm2 per min at the final session (P = 0.02). Cumulative air kerma was 12.7 mGy per minute at the initial session compared with 23.1 mGy per minute at the final session (P = 0.007).
For the lateral plane there was also a significant difference. The dose-area product was 0.365 Gy x cm2 per min at the initial session compared with 0.519 Gy x cm2 per min at the final session (P = 0.03). Cumulative air kerma was 6.2 mGy per minute at the initial session compared with 12.9 mGy per minute at the final session (P = 0.01).
Clinical Significance
According to Lee, considering the multiplicity of the procedure, the statistically significant increase in the radiation dose could be potentially harmful to patients and operators as well. “Since there is no safe margin in the X-ray usage, we should keep the basic action rule—the ALARA principle,” Lee said.
In addition, he recommended checking the AEC system and other measure field functions on the fluoroscopic system.
“Select the best measure field that could minimize the area of Onyx cast in the field to prevent burning of the image field,” Lee said. “We have to do our best to achieve reasonable (not the best) image quality while using an X-ray dose as low as possible.”
Sources:
Sheen JJ, Jiang YY, Kim YE, et al. Increase in fluoroscopic radiation dose in successive sessions of multistage Onyx embolization of brain arteriovenous malformations compared with the first session. J NeuroIntervent Surg. 2018;Epub ahead of print.
Disclosures:
- This study was supported in part by a research grant from Dongkuk Pharma Co Ltd Korea.
- The researchers report no relevant conflicts of interest.
