The goal of this clinical trial is to find out whether lowering the radiation dose to parts of the prostate without visible tumor on MRI can reduce side effects while still effectively treating prostate cancer in men with low or intermediate-risk prostate cancer.
The main questions it aims to answer are:
* Does reducing the radiation dose to healthy prostate tissue lower the risk of bowel and urinary side effects? * Can we maintain good cancer control by keeping a high dose for MRI-visible tumor areas?
Researchers will compare two treatment approaches:
* One group receives a uniform high dose to the entire prostate. * The other group receives a lower dose to healthy prostate tissue and a high dose only to visible tumor areas.
Participants will:
* Receive two sessions of MRI-guided radiotherapy using an MR-Linac. * Complete questionnaires about urinary, bowel, and sexual health before and after treatment. * Have follow-up visits to monitor side effects and PSA levels for up to 2 years.
Men aged ≥18 years
Histological confirmation of prostate adenocarcinoma requiring radical radiotherapy
Gleason score 3+3, 3+4 or 4+3 (ISUP Grade groups (GG) 1, 2 or 3)
MRI-visible tumour(s) of PIRADS v2 grade 3 or higher and able to be delineated on T2 and diffusion-weighted imaging +/- dynamic contrast-enhanced imaging. Tumour nodule visible on MRI should be considered able to be boosted by treating clinician and <2.5cm in maximal dimension. MRI must be performed within 3 months of trial entry
Contraindications to MRI (e.g. pacemaker, potentially mobile metal implant, claustrophobia)
IPSS Score > 19
High grade disease (GG3) occult to MRI-defined lesion. As a guide, any pathology for which you would consider surveillance is allowed outside of the MRI-defined area.
Prostate volume >90cc
Parallel
uniform dose radiotherapy
Radiation27 Gy dose in 2 fractions to the whole prostate+/- seminal vesicles with a 0mm PTV margin using MR-linac
De-escalated dose radiotherapy
RadiationThe benign prostate +/- SV CTV will receive 20 Gy in 2 fractions with a 0mm PTV margin using MR-linac. The intraprostatic tumor masses (on MRI) will receive 27 Gy in 2 fractions. A 4mm GTV to PTV margin will be added to the in-traprostatic MR visible tumour to form PTV 27Gy.
Acute GU toxicity
Physician-reported acute Grade 2 or higher CTCAE GU toxicity observed within 13 weeks of starting radiotherapy
Dosimetry
Estimate the accumulated dose differences between treatment arms in terms of dose to prostate CTV, rectum, urethra and bladder
Late GI toxicity
Physician reported late GI toxicity according to CTCAE v5.0
Biochemical relapse-free survival
Assess biochemical relapse-free survival for 2 years
Severity of erectile dysfunction experienced by patient
The IIEF-5 patient reported outcomes (PROs) assess the acute severity of erectile dysfunction
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