Radiation dose reduction for CT-guided renal tumor cryoablation

OBJECTIVE. The purpose of this article is to retrospectively determine the image quality and degree of radiation dose reduction that is clinically acceptable for CT-guided renal tumor cryoablation. MATERIALS AND METHODS. A total of 15 patients (17 procedures; mean age, 67 years; range, 38-85 years) undergoing clinically indicated CT-guided renal tumor cryoablation procedures were included in this retrospective study. A previously validated noise-insertion tool was used to simulate reduced-dose scans at 75%, 50%, 25%, and 10% of the original dose at four representative phases of the cryoablation procedure. Images obtained at different dose levels were randomized and reviewed by three radiologists blinded to the level of dose reduction, who scored them independently with a 5-point scale (1-5, with 5 the best). Images with a mean score of 3 or higher were considered diagnostically acceptable. The minimal acceptable dose was that at which 90% of images were considered diagnostically acceptable. Interrater agreement was assessed using the weighted kappa statistic. RESULTS. The weighted kappa value was 0.68, indicating substantial agreement among the reviewers. The averaged percentage of diagnostically acceptable images for the four series was 100% for a full dose, 98-100% for the 75% dose level, 94-98% for the 50% dose level, and less than 90% for images obtained at the 25% and 10% dose levels, which was considered unacceptable. CONCLUSION. On the basis of results from 15 patients (17 procedures), images obtained from CT acquisitions at 50% (volume CT dose index, 12.2 mGy) of the original dose level (volume CT dose index, 24.4 mGy) were acceptable for the purpose of CT monitoring of renal cryoablation procedures.