Magnetic resonance imaging-guided focused ultrasound surgery for symptomatic uterine fibroids: estimation of treatment efficacy using thermal dose calculations.

Objective: To study the correlation between the predicted thermal dose volume (TDV) and the actual ablation volumes in MR-guided focused ultrasound surgery (MRgFUS) for symptomatic uterine fibroids, and to follow up the outcome for 12 months post-treatment.

Study Design: Phase-difference fast spoiled gradient-echo MR images were used to analyze thermal change during the energy deliveries of MRgFUS in 60 consecutive patients treated for symptomatic uterine fibroids. The TDV obtained through analysis of these MR images was compared with the non-perfused volume (NPV) measured on post-treatment contrast enhanced T1-weighted images. Final values of TDV ratio and NPV ratio were obtained by dividing these values by original fibroid volume. Patients were followed for 12 months post-treatment to assess symptomatic relief using the symptom severity score (SSS).

Results: Treatments in which we managed to reach a TDV ratio larger than 27% of the treated fibroid yielded a ratio of NPV to TDV of 1.1±0.5, indicating accurate control of the non-invasive procedure. Patient symptoms, as measured by the SSS, continuously decreased from a mean baseline score of 50±22 to 19±12 (P<0.0001) 12 months post-treatment.

Conclusions: At large treatment volumes (exceeding 27% TDV ratio), thermal dose estimates correspond very closely to non-perfused volumes measured immediately post treatment. These large treatment volumes result in continuous clinical improvement throughout the first 12 months after MRgFUS.