Potency pReservation In Prostate cAncer Patients Treated With UltraSound-guided Low-dose Rate Brachytherapy

The purpose of this study is to develop and evaluate a Magnetic Resonance (MR) fusion 3D Ultrasound (US) guided Low dose rate (LDR) brachytherapy technique that significantly spares prostatic neurovascular bundles (a bundle of nerves and vessels that run beside the prostate) and penile bulb (base of the penis), while still trying to effectively treat the prostate cancer.

Low dose rate (LDR) brachytherapy is an excellent treatment strategy for patients with prostate confined cancers, achieving high curative rates. However, LDR brachytherapy has been linked with long-term erectile dysfunction (ED), with a broad range of reported incidence in the literature.

The pathophysiology associated with ED is complex and variable among different prostate cancer treatment strategies. In the post radical prostatectomy (RP) setting, ED is usually an immediate phenomenon and associated with neuropraxia caused by trauma and inflammation (Nandipati 2006). On the contrary, external beam radiotherapy (EBRT) related ED frequently occurs between 6-24 months and is believed to be vasculogenic in nature and caused by veno-vascular luminal occlusion (Mulhall et al. 2005) that culminates into fibrosis of the corporal tissue. In the post brachytherapy setting, seems plausible that a combination of both nerve and vascular damage are involved in the ED pathogenesis as erectile scores seem to reduce in the first months post implant (likely due to trauma) followed by a subsequent recovery and then, a gradual decline (Mabjeesh 2005).

Despite a more complex pathophysiology, rates of ED post LDR brachytherapy seem to be lower than post EBRT or RP treatment (Crook 2010, Putora 2015). This may be associated with a significantly lower degree of trauma to the surrounding healthy tissue compared with trauma caused by RP and a more conformal dose around the prostate when contrasted with EBRT. In this regard, brachytherapy delivers a lesser dose to important structures previously correlated with an erectile function such as the internal pudendal artery (IPA), penile bulb, corpus cavernosum and possibly the neurovascular bundle.

Currently, some strategies have been developed in an attempt to minimize ED post radiotherapy. In the POTEN-C clinical trial (NCT03525262), 120 patients are being randomized to stereotactic ablative radiotherapy with or without neurovascular sparing (neurovascular bundle, IPA and penile bulb/corpus carvenosum) with ED as the primary endpoint. Although the concept is intriguing, LDR brachytherapy has superior dose conformality and hence, a better chance to reduce radiation dose to the surrounding structures involved in the erectile function while still effectively treating the prostate cancer.

Eligibility Criteria:
Inclusion Criteria:

* Biopsy-confirmed adenocarcinoma of the prostate
* NCCN-defined low- or favourable intermediate-risk prostate cancer patients
* All pathological cores confined to one lobe of the prostate (minimum of 12 cores sampled), unless a recent multiparametric prostate MR-scan (mpMR) (with \< 6 months from the enrollment date) indicates a dominant intra-prostatic lesion (DIL) located at the prostatic lobe where a higher number of cores and Gleason score was found positive. PIRADS v2 score 3-5 lesions are considered DILs.
* No or mild erectile function impairment (score ≥18 in International Index of Erectile Function- 5 \[IIEF-5\] without PDE-5 inhibitor assistance)
* Sexually active
* No contraindications to prostate LDR brachytherapy

Exclusion Criteria:

* Core positivity in both lobes of the prostate with no DIL detected on mpMR
* mpMR suggesting presence of DILs in both lobes of the prostate
* Contraindications to receiving a MR-scan
* Medically unfit for general and/or spinal anesthesia
* IPSS score \> 15
* Inflammatory bowel disease
* Prior abdominal-perineal resection
* Presence of distant metastases and/or nodal disease
* Older than 75 years of age
* Use of cytoreductive prostate treatment (including 5 alpha-reductase inhibitors)
* NCCN-defined unfavourable intermediate or high-risk prostate cancer
* Signs of extra-capsular extension or seminal vesicle involvement on MR-scan
* Prior TURP
* \> 3mm of median lobe protrusion to bladder measured in mpMR (Roeloffzen 2011)
* Prior RT to the pelvis
* Significant artifact on MR-Scan (e.g. caused by hip prosthesis)