EREctile Function Preservation for Prostate Cancer Radiation Therapy (ERECT); a Prospective Phase II Trial

Rationale: Erectile dysfunction is a frequent side effect of external beam radiotherapy (EBRT) for prostate cancer. To date, anatomy-based treatments that are designed to spare relevant neurovascular structures such as the internal pudendal artery and neurovascular bundles have not yet been routinely implemented in clinical practice. The implementation of magnetic resonance imaging (MRI) in treatment planning and introduction of Intensity Modulated Radiotherapy (IMRT) and Volumetric Arc Therapy (VMAT) have improved treatment precision and enabled anatomy-based EBRT and neurovascular-sparing treatments. Spratt et al. have conducted a single-arm phase 2 study to investigate the effect of vascular-sparing IMRT treatments, and found a significantly improved 2-year erectile function (78%, 95% confidence interval [CI] 71-85%) compared to conventional radiotherapy (42%, 95% CI 38-45%; p<0.001) or nerve-sparing prostatectomy (24%, 95% CI 22-27%; p<0.001). In the UMCU, the state-of-the-art MRI linear accelerator (MR-Linac) has recently been introduced. This new system allows radiation delivery under high-precision MRI visualization. The MR-Linac is therefore the most suitable technique for neurovascularsparing external beam radiotherapy treatments. Such neurovascular-sparing treatments may substantially improve post-radiotherapy erectile function outcomes and can thus improve quality of life without substantially compromising oncologic outcome.

Objective: To investigate preservation of erectile function after MR-guided radiotherapy with neurovascular-sparing in patients with localized prostate cancer.

Study design: The EREctile function preservation for prostate Cancer radiation Therapy (ERECT) trial is a prospective, single-center, phase 2 trial. Patients will be treated with the MR-Linac up to 5 fractions of 7.25 Gy with neurovascular-sparing. All fractions will be delivered over the course of 2 and a half weeks.

Study population: Men with low- and intermediate-risk adenocarcinoma of the prostate, clinical stage T1c-T2c, and Gleason ≤7, and iPSA <20 µg/L (NCCN risk categories). Patients with pT1a/b tumor diagnosis after transurethral resection of the prostate (TURP) are included, patients with "bulky" iT3 tumor diagnosis are excluded. Baseline erectile function score according to the International Index of Erectile Function (IIEF-5) questionnaire of at least 17.

Intervention: All patients will receive MR-Linac treatment consisting of 5 fractions of 7.25 Gy with neurovascular sparing, Fractions will be delivered with an overall treatment time of two and a half weeks.