Following completion of informed consent and enrollment on the study, subjects will undergo IRE procedure targeting the focal csPCa performed by board certified Urologist with proficient prior training in the technique. Prior to NanoKnife treatment, subjects will receive an antibiotic of choice selected by the treating physician via intravenous infusion to reduce the chance of infection. A negative urine culture will be obtained prior to treatment. In the OR, subjects will be placed in the dorsal lithotomy position under sterile technique. The NanoKnife procedure will be carried out under general anesthesia. A Foley catheter will be placed to aid in draining the bladder during treatment.

The area of the prostate that was positive for cancer based on the transperineal prostate biopsy will be targeted for ablation via the NanoKnife System. An MRI/TRUS fusion device probe will be placed in the rectum and the prostate will be visualized in both sagittal and axial views. The ultrasound grid which was used during the mapping biopsy will be oriented using anatomical landmarks and used to identify the location of the positive biopsy cores. The NanoKnife Single Electrode Probes will be percutaneously inserted into the prostate through the perineum using UroNav MRI/TRUS fusion system as guidance. The location of the probes will be documented via ultrasound imaging.

After placement of the NanoKnife probes in the prostate and immediately prior to NanoKnife treatment, a nondepolarizing neuromuscular blocking agent will be administered to reduce skeletal muscle contraction which is associated with the use of the NanoKnife System. The pulse treatment dose will be determined using standard protocol and a pre-treatment checklist will be performed prior to ablation. Post ablation assessment will be performed by assessing changes in voltage parameters during treatment and after confirmation of adequate ablation the probes will be removed. An immediate post ablation MRI will also be assessed to determine the effectiveness of ablation. The Foley catheter will be left in place after the procedure and removed at the discretion of the treating physician. Any adverse events (AEs) will be recorded on the AE CRF. Patients will be discharged from the hospital with a foley catheter and scheduled for a void trial prior to removal. The void trial will include a post void residual to confirm safety for catheter removal. Patients will follow up with treating physician in 1–2 weeks post ablation and will be eligible to undergo RT planning no sooner than 6 weeks post IRE.

After consent, eligibility verification, and IRE patients will undergo CT/MRI simulation and radiotherapy planning. Patients will receive treatment to the prostate + seminal vesicles to a dose of 32.5 Gy in 5 fractions or 22 Gy in 2 fractions. The rationale behind the selected dose relates to an estimated a/b ratio of 2.7 for PCa supported by ultra-hypofractionation trials and a large meta-analysis [5, 6]. With a lower α/β value, PCa should have an improved therapeutic ratio with ultra-hypofractionation. Furthermore, if the α/β formalism and assumed values for PCa are correct and one maintains a constant biologically effective dose for normal tissues, there is the potential for increased tumor control with ultra-hypofractionation in this setting. The dose selected for this trial is less than the therapeutic dose when radiation alone is used for intact PCa (7–8 Gy x 5 fractions or 12.5–14 Gy x 2 fractions) but has a biological effective dose of > 100 Gy based on the α/β value of 2.7 Gy.

Full details regarding radiation therapy treatment planning/simulation set-up, contouring, PTV and OAR prescription dose constraints, adaptive MR-Linac planning can be found in Supplemental File 1.

Subjects will be seen on their final day of radiotherapy at which time blood and urine samples will be collected for research purposes as outlined in treatment protocol and previously discussed at time of informed consent/enrollment. Subjects will also complete EPIC-CP, IPSS and IIEF-5 questionnaires on the final day of RT and evaluated for any AEs per CTCAE v5.0 definition. They will be informed regarding expected side effects following treatment and will be counseled to contact treating physician/medical provider for any concerning side effects following treatment.

A proportion of patients undergoing prostate radiotherapy can expect an increase in urinary frequency or urgency. If this becomes bothersome to the patient, medication to alleviate symptoms can be prescribed at the discretion of the treating radiation oncologist and documented in patient chart. Serious bowel symptoms during time of prostate radiotherapy are rare. If patients develop rectal urgency, tenesmus or diarrhea, medication to alleviate symptoms can be prescribed at the discretion of the treating radiation oncologist and documented in patient chart.

Subjects will be scheduled for post RT follow up appointments at 3, 6, 9, 12 and 24 months. At 3, 6, 9, 12 and 24 month follow up visits all patients should undergo physical exam including vital signs, height, weight, PSA, repeat EPIC-CP, IPSS, IIEF-5 and screened for adverse events.

At the 12 month follow up appointment, patients will undergo pelvic MRI, PSMA PET-CT, collection of blood and urine specimen as well as repeat transperineal 14-core template biopsy (Additional biopsies of targeted lesion/ and new PSMA PET/CT or mpMRI identified lesions will also be performed) using UroNav’s ultrasound/MRI fusion technology. These prostate biopsy specimen will be analyzed for oncologic effectiveness as part of the primary objective of the study. Planned trial procedures are outlined in Table 1.

Adverse event (AE) monitoring and reporting is a routine part of every clinical trial. CTCAE v5.0 will be utilized to grade any potential adverse events in relation to the trial at specified time points and any unscheduled time points while patient is on the study. All adverse events will be recorded on a subject specific AE log which will be maintained by the research staff and kept in the subject’s research chart. All AEs and SAEs occurring on this study will be reported to the Institutional review board (IRB) of Weil Cornell Medicine according to the IRB policy and as outlined in the current approved study protocol. All SAEs and AEs reported during this study will be followed until resolution or until the investigator confirms that the AE/SAE has stabilized, and no more follow-up is required.

REDCap will be used to collect and maintain all data related to the study including details of treatment, toxicity, efficacy, and AE data for all enrolled subjects as outlined in the trial protocol and per WCM IRB approved protocols. Security measures to protect patient data include firewall technology, database level security with minimum necessary privileges is routinely employed. Data is backed up periodically per institutional standard operating procedures and is stored for at least 5 years following the termination of the study. The Weil Cornell Medicine Data Safety Monitoring board serves as the central monitoring body and operates in concordance with the guidelines in the 2001 National Cancer Institute-approved data and safety monitoring plan for Weill Cornell Medicine Meyer Cancer Center. Additional information regarding data management and safety monitoring can be obtained online via WCM IRB website.

For the phase II portion of the trial, it is assumed that the historical control value for the. proportion of patients who are cancer free at 1-year follow-up is 0.80 for the standard of care comparison.

The trial is designed to detect an increase in the proportion of patients who are csPCa free at 1-year follow-up to 0.95 (increase of 0.15). An exact binomial test with a 10% one-sided significance level will have 94.3% power to detect the difference between the null hypothesis proportion of 0.8 and the alternative proportion of 0.95 when the sample size is 42. All subjects who received any protocol treatment will be included in the evaluation of adverse events from the time of their first treatment with RTIRE. All subjects included in the study will be assessed for treatment efficacy if they have received any protocol IRE and radiation treatments.

The primary analysis for the Phase 2 portion will include the patients that were part of the feasibility evaluation (N = 10), the patients who were part of the safety run-in for the 2 fraction RT schedule (N = 10), and the additional patients who were accrued after the run-in phase (N = 22) for a total of N = 42. The analysis will use a one-sided exact binomial test to determine if the observed proportion of patients who are cancer free at the one-year follow-up is greater than 0.80. In addition, the proportion of patients who are cancer free at the one-year follow-up will be estimated with a binomial point estimate and 80% binomial confidence interval. We will also generate and report the 95% confidence interval since this is more familiar to the research community.

The maximum grade of a specific AE experienced by a patient will be used. Unique AEs and the grade will be summarized as frequency and relative frequency. The proportion of patients who experience a grade 3 or higher (and grade 4 or higher) will be estimated with a binomial point estimate and corresponding 95% confidence interval. The QOL measures will be plotted over time for each patient and an average curve will be superimposed. The change in QOL from baseline will be summarized at each timepoint by the mean, standard deviation, median, minimum, and maximum value. PSA values will also be plotted over time for each patient with an average curve superimposed. The proportion of patients who experience a biochemical recurrence by one year will be estimated with a binomial point estimate and 95% confidence interval. The time to biochemical recurrence will be estimated with a Kaplan-Meier estimator.