Objective To assess the feasibility of targeting recurrent gynaecological tumours with MR guided high intensity focused ultrasound (MRgHIFU).Methods 20 patients with recurrent gynaecological tumours were prospectively scanned on a Philips/Profound 3 T Achieva MR/ Sonalleve HIFU system. Gross tumour volume (GTV) and planning target volume (PTV) were delineated on T 2W and diffusion-weighted imaging (DWI). Achievable treatment volumes that (i) assumed bowel and/or urogenital tract preparation could be used to reduce risk of damage to organs-at-risk (TVoptimal), or (ii) assumed no preparations were possible (TVno-prep) were compared with PTV on virtual treatment plans. Patients were considered treatable if TVoptimal ≥ 50 % PTV.Results 11/20 patients (55%) were treatable if preparation strategies were used: nine had central pelvic recurrences, two had tumours in metastatic locations. Treatable volume ranged from 3.4 to 90.3 ml, representing 70 ± 17 % of PTVs. Without preparation, 6/20 (30%) patients were treatable (four central recurrences, two metastatic lesions). Limiting factors were disease beyond reach of the HIFU transducer, and bone obstructing tumour access. DWI assisted tumour outlining, but differences from T 2W imaging in GTV size (16.9 ± 23.0%) and PTV location (3.8 ± 2.8 mm in phase-encode direction) limited its use for treatment planning.Conclusions Despite variation in size and location within the pelvis, ≥ 50 % of tumour volumes were considered targetable in 55 % patients while avoiding adjacent critical structures. A prospective treatment study will assess safety and symptom relief in a second patient cohort.Advances in knowledge Target size, location and access make MRgHIFU a viable treatment modality for treating symptomatic recurrent gynaecological tumours within the pelvis
