INTRO High intensity focused ultrasound (HIFU) is used to locally heat and destroy diseased or damaged tissue by ablating it.
This study aims to explain the fundamentals of HIFU, evaluate its role and efficacy in the treatment of prostate cancer (PC) also based on our experience, highlight the controversies associated with it, and compare the new technological devices guided by mp MRI-US with the previous generation of devices guided solely by ultrasound.
HIFU device consists of a working console connected to a transrectal probe (Fig.1) that doubles as an ultrasound scanner and literally "fires" a high-intensity ultrasound beam at a precise point.
The US energy heats the tissue to a temperature of 70 to 80°C, which results in thermal shock with mechanical damage by melting of cellular lipid membranes, protein denaturation, coagulation, necrosis, gas bubble formation and cavitation [1].
INDICATIONS Initially, the only indication for the use of HIFU was for patients with localized PC who were not candidates for general surgery of monolateral small-volume, low-Gleason tumors.
However, with the accumulation of clinical experience and expansion of research protocols, these indications have expanded allowing focal therapy to be included in incidental finding of prostate cancer after transurethral resection (TUR), in locally advanced tumor as adjuvant therapy for local bulking, in salvage therapy of relapsed PC after radical prostatectomy, after radiotherapy or hormone therapy, and for hormone-resistant PC [2-3].
CONTROINDICATIONS Relative: - Gland size: not so much volume but the most important criterion is the AP diameter at the site of the lesion. - Calcifications greater than 1 cm create acoustic barrage and restrain US.
A turp may be indicated in some cases to remove the calcification. - Brachytherapy semi, which dissipates energy. - Small rectum and a rectal wall damaged by previous prostate/rectal therapy or IBD [4].
The only absolute contraindication is radiation therapy x 2 (radiation therapy + salvage radiation therapy), because the rectum has undergone a significant dose of radiation.
MULTI-PARAMETRIC RESONANCE IMAGING OF THE PROSTATE - mpMRI is indispensable for staging the disease locally and accurately localizing small target lesions (of ≥0.5 mL), thus allowing selective targeted ablation and sparing radical procedures over the entire gland.
Less well identifies mutifocal infiltration, present in 67-87% of prostate tumors. - Lower treatment time. - mpMR also identifies vital structures (rectum, neurovascular bundle, bladder neck and membranous urethra), so as to treat while respecting safety margins, avoiding significant side effects, such as erectile dysfunction, incontinence or vesicorectal fistulas. - It also assesses seminal vesicle invasion or extracapsular extension (more aggressive treatments are better in these cases). - It can also be used as a follow-up after focal therapy, both with and without biochemical recurrence, and possibly re-biopsies [5].
PREPARATION The patient is in lateral decubitus, under spinal anesthesia, with a bladder catheter for more room for action.
Legs are secured to the tailboard with straps.
A disposable kit is mounted on the transrectal probe.
PRE-OPERATIVE PLANNING: mpMRI AND FUSION WITH US After importing the MRI images into the dedicated software, we draw the volumes of the whole prostate (we draw at least 3 ROIs toward the apex and 3 toward the base to be as accurate as possible) and of the lesion, at the same way.
In the real time frame we obtain in addition the elastic fusion (Fig.2) With the HIFU software the prostatic volumes are delineated at the same way, also establishing the safety margins with the rectal wall (to prevent vesico-rectal fistulas) and between the anatomical apex and the start of treatment (to prevent incontinence).
Subsequently the mpMRI images are transferred to the software, which automatically merges the US and RM by synchronizing the scan plans.
This allows you to identify the volume of the lesion on ultrasound images.
Sonication starts successively, which heats small targets at a time, so it is necessary to use multiple sonications with volumetric steering that determines the translation of the beam to ablate the entire target area (Fig.3).
A target lesion alone or the entire prostate (first one lobe and then the other) can be treated, guided by real-time ultrasound MRI.
The ablation has a variable duration from 20 minutes (focal lesion or quadrant) to about 1 hour (whole gland).