Dose De-escalation in Prostate Radiotherapy Using the MRL

The goal of this feasibility study is to learn about dose de-escalation in the treatment of men with intermediate risk prostate cancer.

The main question it aims to answer is the technical feasibility of treating prostate cancer with toxicity-minimising radiotherapy on an Magnetic Resonance Linear Accelerator (MR-linac). It will also examine gastrointestinal and genitourinary toxicity in the acute and late setting post radiotherapy as well as Prostate-Specific antigen (PSA) control up until 2 years post treatment.

Participants will be treated with radiotherapy to the prostate with which will be given in 30Gy in 5 fractions to the whole prostate and 45Gy in 5 fractions to the dominant lesion.

DESTINATION is a single centre phase II non-randomised study in men with intermediate risk localised prostate cancer.

The aim is to establish the technical feasibility of treating prostate cancer with toxicity-minimising radiotherapy on an MR-linac.

20 men will be recruited to take part. All radiotherapy will be delivered on the MR-linac. The whole prostate with no margin will be treated to 30 Gray (Gy) in 5 fractions (i.e. dose to 95% of the Clinical Target Volume prostate should receive 30 Gy (D95%CTVp= 30 Gy)). The dominant lesion (Gross tumour volume (GTV)) as defined on pre-biopsy multiparametric magnetic resonance imaging (mpMRI) plus a 4mm intra-prostatic margin (GTV4mm) will be treated to 45 Gy in 5 fractions, providing standard organ at risk (OAR) constraints can be met. If not, then dose coverage of the GTV will be reduced until the OAR constraints are met (i.e. isotoxic dose escalation). OAR constraints will be as per international standard levels, and largely consistent with the PACE B trial.

The primary end point will be assessed once 14 patients have completed their radiotherapy treatment on the MR-Linac. If any of the first 14 patients do not complete all five fractions planned, then recruitment will continue until we have 14 assessable patients. The analysis population for the primary endpoint will be defined as those patients who have completed all five fractions of stereotactic body radiotherapy (SBRT) as intended.

If shown to be feasible a total of 20 patients will be recruited to enable a better estimation of the toxicity rates and to further technical proficiency with this technique.

Eligibility Criteria:
Inclusion Criteria:

* Men aged ≥18 years
* Histological confirmation of prostate adenocarcinoma requiring radical radiotherapy
* Gleason score 3+3, 3+4 or 4+3 (Grade groups 1, 2 or 3)
* MRI stage T2 or less (as staged by AJCC TNM 2018)
* MRI-visible tumour(s) of Prostate Imaging-Reporting and Data System (PIRADS) v2 grade 3 or higher on T2 and diffusion-weighted imaging and/or dynamic contrast-enhanced imaging with concordant pathology
* Tumour nodule visible on MRI occupying \<50% of prostate on any axial slice and \<50% total prostate volume
* PSA \<20 ng/ml prior to starting androgen deprivation therapy (ADT)
* Patients can be concurrently treated with androgen deprivation therapy if this would be standard of care. Luteinizing hormone-releasing hormone (LHRH) analogues or Bicalutamide are permitted. ADT is not mandatory where this would usually be omitted.
* World Health Organisation (WHO) Performance status 0-2
* Ability of the participant understand and the willingness to sign a written informed consent form.
* Ability/willingness to comply with the patient reported outcome questionnaires schedule throughout the study.

Exclusion Criteria:

* Contraindications to MRI (e.g. pacemaker, potentially mobile metal implant, claustrophobia)
* IPSS 19 or higher
* High grade disease (GG3) occult to MRI-defined lesion
* Post-void residual \>100 mls, where known
* Prostate volume \>90cc
* Comorbidities which predispose to significant toxicity (e.g. inflammatory bowel disease) or preclude long term follow up
* Unilateral or bilateral total hip replacement, or other pelvic metalwork which causes artefact on diffusion-weighted imaging
* Previous pelvic radiotherapy
* Patients needing \>6 months of ADT due to disease parameters.
* Previous invasive malignancy within the last 2 years excluding basal or squamous cell carcinomas of the skin, low risk non-muscle invasive bladder