AJR: Interventional radiation doses safe

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Interventional radiology sustains its auspices, a noninvasive alternative with widely varying—but safe—levels of radiation administered to patients, according to a study published in the July issue of the American Journal of Roentgenology.

Interventional radiology is less invasive and more cost-effective option than surgery, and procedure volume is growing, with a large proportion of procedures guided by CT. However, whether performed as fluoroscopic (continuous) or intermittent procedures, radiation doses exceed those of standard CT exams, though clinicians lack a clear handle on estimated doses for many procedures, explained Shuai Leng, PhD, and co-authors from the department of radiology at Mayo Clinic in Rochester, Minn.

Given the variable imaging techniques required for different procedures, Leng and colleagues estimated effective and skin doses for five interventional procedures: cryoablation, aspiration, biopsy, drain and injection. The retrospective calculations were based on 571 CT-guided procedures performed at Mayo between March and July of 2008. Just under half of patients were females, with an overall mean age of 60 years.

Cryoablation delivered far higher doses than all other procedures—mean skin dose was 728 mGy and effective dose 120 mSv for the procedure. The latter amounted to roughly 10 to 15 times the effective dose of a routine abdomen and pelvis scan.

Although the figures varied widely among patients, the authors pointed out that none of the doses exceeded the threshold for nonpermanent skin injury.

Mean skin doses for other procedures were estimated at 195 mGy for injection, 152 mGy for drain, 130 mGy for aspiration and 128 mGy for biopsy.

Effective doses were calculated by multiplying dose length-product by a conversion factor set at 0.018 for intermittent procedure mode and 0.015 for helical mode. Doses were estimated at 25, 20, 14 and 9 mSv for drain, aspiration, biopsy and injection, respectively.

Leng and colleagues noted that although intermittent mode tended to contribute higher doses to skin, helical mode was responsible for most of the effective dose exposure, due to the limited scan range of intermittent mode in comparison to the longer ranges of helical scans. Both modes were used in the majority of procedures completed at Mayo.

The authors stressed the significance of dosimetry variations between procedures, patients and institutions; for the latter two, data from additional institutions and non-phantom-based estimations would both improve the accuracy of their estimates.

Similarly, the authors underscored the importance of individual institutions reviewing their own procedure protocols to determine radiation dose improvements. As a result of the present findings, clinicians at Mayo have since halved the radiation dose administered for cryoablation, recognizing the disparate dosimetry needs of individual exams and procedures.

“Accuracy and safety are critical in interventional procedures because errors may result in severe consequences, such as an inaccurate diagnosis (e.g., biopsy or aspiration that missed the pathologic abnormality), incomplete therapy, or damage to adjacent critical tissues and organs,” wrote Leng and co-authors.

“Therefore, the benefits from CT guidance outweigh the potential radiation risk for medically justified procedures. Furthermore, even for lengthy procedures, the skin dose falls below the threshold where transient skin injury has been observed,” they continued.

Leng and colleagues concluded that their findings showed that deterministic harm from interventional procedures is “extremely unlikely.”