CLINICAL STUDY Safety and Therapeutic Efﬁcacy of Complete or Near- Complete Ablation of Symptomatic Uterine Fibroid Tumors by MR Imaging–Guided High-Intensity Focused US Therapy Min Jung Park, MD, Young-sun Kim, MD, Hyunchul Rhim, MD, and Hyo Keun Lim, MD ABSTRACT Purpose: To evaluate the safety and therapeutic efﬁcacy of magnetic resonance (MR) imaging–guided high-intensity focused ultrasound (US) ablation of symptomatic uterine ﬁbroid tumors with an immediate nonperfused volume (NPV) ratio of 80% or more. Materials and Methods: A total of 79 women with 117 uterine tumors were treated with MR-guided high-intensity focused US ablation. Immediate NPV, complications, and therapeutic efﬁcacy (tumor volume reduction ratio and symptom severity score [SSS] decrease at 3-mo follow-up) were retrospectively assessed. Statistical comparisons of the frequency of complications and therapeutic efﬁcacy were performed between patients with NPV ratios of at least 80% and less than 80%. Results: Technical success was achieved in 93.7% of cases (n ¼ 74) of cases, and the immediate NPV ratio was 62.7%  25.5. Twenty-four patients exhibited an NPV ratio of at least 80% (89.7%  5.8), and 50 patients showed an NPV ratio of less than 80% (49.8%  20.7). All complications were minor in severity, and the incidences were not signiﬁcantly different between groups (P 4 .05). The 3-month volume reduction ratio was signiﬁcantly greater in patients with an NPV ratio of at least 80% (0.43  0.17) than in those with an NPV ratio of less than 80% (0.20  0.26; P ¼ .002), although the decreases in SSS were not signiﬁcantly different (20.9  19.6 vs 12.1  10.1; P ¼ .097). Conclusions: In MR-guided high-intensity focused US ablation of symptomatic uterine ﬁbroid tumors, achievement of an immediate NPV ratio of at least 80% is safe, with greater tumor volume shrinkage compared with cases with a lower NPV ratio. ABBREVIATIONS FDA = Food and Drug Administration, NPV = nonperfused volume, SSS = symptom severity score, UAE = uterine artery embolization In determining how extensively magnetic resonance (MR) imaging–guided high-intensity focused ultrasound (US) ablation of uterine ﬁbroid tumors (ie, leiomyomas) should be performed, the balance between therapeutic efﬁcacy and safety is important, as is the case for other interven- tional or surgical modalities. Speciﬁcally, providing undue consideration to therapeutic efﬁcacy may result in increased incidence or severity of complications, whereas underemphasizing may result in insufﬁcient treatment, and in turn reduce therapeutic efﬁcacy. Because MR-guided high-intensity focused US therapy has a relatively short history, protocols and guidelines for clinical applications tend to lean more toward the safety aspect. For instance, the guidelines provided by the Food and Drug Admin- istration (FDA) of the United States previously limited the treatment of uterine ﬁbroid tumors to only 50% of the & SIR, 2014 J Vasc Interv Radiol 2014; 25:231–239 http://dx.doi.org/10.1016/j.jvir.2013.11.011 This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2011-0006504). None of the authors have identiﬁed a conﬂict of interest. From the Department of Radiology (M.J.P.), Research Institute of Radiological Science, Severance Hospital, Yonsei University College of Medicine, Seoul; and Department of Radiology and Center for Imaging Science (Y.s.K., H.R., H.K.L.), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. Received July 29, 2013; ﬁnal revision received November 8, 2013; accepted November 9, 2013. Address corre- spondence to Y.s.K., Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwondong, Gangnam-gu, Seoul 138-225, Korea; E-mail: young- skim@skku.edu