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Real time magnetic resonance guided focused ultrasound for focal therapy of locally confined low-intermediate risk prostate cancer: feasibility and preliminary outcomes

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Introduction and Background

Although prostate cancer is often multifocal, the volume of the largest / index tumour has been found to be as good a predictor of recurrence after radical prostatectomy as the total tumour volume. The index lesion is often imageable on mp-MRI. Using its localizing strength, multi-parametric MRI (mp-MRI) utilizing T2-weighted, diffusion weighted (DWI) and dynamic contrast enhanced (DCE) MRI, has increased opportunities in management, in particular, focal therapy of prostate cancer. Additionally, MR thermometry allows real time peri-procedural in-bore monitoring to ensure selective and adequate tumor ablation.

The ExAblate MRgFUS system (InSightec. Ltd, Haifa, Israel) combines standard 1.5/3T MRI scanner with HIFU (High Intensity Focused Ultrasound) energy that is transmitted from a phased array endorectal transducer of 990 elements embedded in a probe with circulating degased water in a temperature of 14°C (Figure 1). The treatment is performed by macrosonications that are fan-like batches of nominal subsonications. Each subsonication itself is a column-like clustering of points to which energy is continuously targeted. During sonications the system acquires thermal imaging that is displayed to the user in terms of temperature accumulated dose.



The goal of this study is to develop preliminary data to evaluate the safety and effectiveness of focal MRgFUS treatment of low-intermediate risk prostate cancer. A total of 8 patients will be treated in our institute under this Phase 1 study.


Materials and Methods

7 patients (age range 56 – 67 years), 4 with Gleason 6 (3+3) and 3 with Gleason 7 (two with 3+4, and one with 4+3) prostate cancer (PCa) on a prior biopsy were consented and enrolled in the study. Each patient was assessed for eligibility by mp-MRI followed by transrectal ultrasound guided extended mapping biopsy. Six MRI visible cancerous foci on mp-MRI were identified on 5 of the 7 patients. Two patients did not have visible cancerous foci on mp-MRI. Transrectal 16- core mapping biopsy plus additional sample from each MR target was performed as per protocol. Proximal end of each biopsy sample was inked. Mapping biopsy results again revealed Gleason 6 PCa in 4 patients and Gleason 7 PCa in 3 patients without tumor upgrade. CT of the pelvis was performed in all patients to rule out calcification in the treatment beam path.

 In five patients, 6 sites of tumor were visible on MRI and the treatment was targeted to the sites. Since the tumor was not visible on T2WI in the other 2  patients, the treatment target volume included three sectors from which the cores were positive. MRgFUS treatment was performed under general anaesthesia approximately one month after the biopsy in all patients. Foley’s catheter was placed prior to treatment for continuous bladder drainage in 6 of 7 patients. Suprapubic catheter was placed in one patient since the site of MRI visible target was directly anterior to the urethra. The suprapubic catheter was clamped following the treatment and was also discharged on a Foley catheter.

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