Cryotherapy for posterior lesions of the prostate: the hydrogel technique

Abstract

While radical prostatectomy and radiotherapy have robust long-term cancer control success for localised prostate cancer, the whole-gland treatment approaches carry a certain degree of negative impact on patients’ functional outcome [1]. Focal therapy targets only the cancerous foci within the prostate and thus minimises morbidity and complications. Cryotherapy as one of the most established focal therapy tools has demonstrated satisfactory oncological and functional results [2]. However, posterior lesions have been a concern for cryotherapy due to proximity to the rectum. It has been shown that while the temperature of −20°C is the threshold required to result in coagulative necrosis of tumour cells and often cryotherapy achieve a targeted temperature of −40°C, damage to surrounding healthy tissue can occur in normal tissue at −15°C [3]. Hydrogels are injectable viscous semi-liquid compounds comprised mostly of water with a hydrophilic polymer matrix giving structure to the substance. They can be polyethylene glycol (PEG) or hyaluronic acid-based products. De Castro Abreu et al. [4] have demonstrated the feasibility of adopting hydrogel into cryotherapy in a cadaver model by expansion of the Denonvilliers’ space. In a porcine model, Lam and Ng [5] have verified the temperature insulation ability of hydrogel. In the present clinical study, we illustrate and guide the usage of the hydrogel technique in cryotherapy for posterior lesions of the prostate. We aimed to assess the feasibility of such a technique in expanding the use of cryotherapy for posterior lesions. Cryoablation is performed with fusion software platform (Trinity® system: KOELIS, La Tronche, France). Preoperatively, the patient's MRI images are registered for subsequent fusion and ablation planning. After general anaesthesia, the patient is positioned in the Lloyd-Davies position. The perineum is shaved and prepared with antiseptic solution to facilitate subsequent hydrogel injection and cryoablation (Video S1). A TRUS probe is inserted into the rectum to visualise the prostate. Normal saline (10 mL) is injected by a midline puncture, through the perirectal fat under Denonvilliers’ fascia, to hydrodissect and develop the plane between the prostate and rectum. Keeping the TRUS probe parallel to the posterior prostate surface will help keep the needle in the correct trajectory and increase the ease of needle visualisation. Moving the needle right to left and anterior to posterior can help ensure the needle not being in the rectal wall or prostate capsule. Subsequently, the syringe of normal saline is replaced by hydrogel (Barrigel®; PaletteLife Sciences, Santa Barbara, CA, USA), which is injected slowly into the anterior perirectal fat while pulling the syringe backwards under continuous TRUS guidance. A total of 9 mL of Barrigel is used. Unlike the case of pre-radiotherapy spacer injection, in which we aim at delivering an even distribution of hydrogel between the prostate and rectum, in the case of focal cryotherapy one may opt for tailor-making the hydrogel distribution according to the laterality of the lesion (Fig. 1). Either way, the prostate is lifted up from the rectum, creating an extra buffer distance for subsequent ice-ball expansion. After hydrogel injection, cryoablation (ICEfx™ Cryoablation System; Boston Scientific Corp., Marlborough, MA, USA) is performed with a full-grid guidance under fusion software navigation. Contouring of the prostate and hydrogel location on TRUS images allows us to visualise the final configuration of hydrogel between the prostate and rectum during ablation planning (Fig. 2). Once the contouring has been completed, the cryoablation needle position needs to be planned and registered. Eventual ice-ball configuration is simulated on the fusion software in order to ensure adequate ablation coverage (Fig. 2). Alternatively, as per other conventional practices of cryoablation, the cryoablation needles can be positioned free-hand wi