Abstract #4048

Feasibility of MR guided High Intensity Focused Ultrasound (MRgHIFU) for treating recurrent gynecological tumours: comparing T2W imaging and diffusion weighted imaging (DWI) for treatment planning

Sharon L Giles^1,2, Jessica M Winfield^1,2, Ian Rivens³, Katja De Paepe¹, Veronica A Morgan², Georgios Imseeh⁴, Gail R ter Haar³, Alexandra Taylor⁴, and Nandita M deSouza¹

¹CRUK Cancer Imaging Centre, Institute of Cancer Research, London, United Kingdom, ²CRUK Cancer Imaging Centre, Royal Marsden Hospital, London, United Kingdom, ³Therapeutic Ultrasound, Institute of Cancer Research, London, United Kingdom, ⁴Gynae-Oncology, Royal Marsden Hospital, London, United Kingdom

MR guided high intensity focused ultrasound (MRgHIFU) treatment plans were generated for 16 patients with recurrent gynecological tumors. Gross tumor volumes (GTV) defined on diffusion-weighted imaging using an echo-planar and turbo-spin echo technique (EPI-DWI, TSE-DWI) were approximately 20% smaller than GTV defined on T2W imaging, but did not result in sequence-dependent differences in planning target volume (PTV). PTVs were more easily defined on DWI. However, there were clinically relevant discrepancies (>4 mm) between T2-defined and DWI-defined PTV locations, worst in the phase-encode direction using EPI-DWI, that need to be accounted for if incorporating DWI into MRgHIFU treatment planning.

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