MRI-guided vs CT-guided SABR for prostate cancer: results from MIRAGE study

MRI-guided vs CT-guided SABR for prostate cancer: results from MIRAGE study

10 January 2023

The phase III MIRAGE trial1 compares the two imaging modalities used for image-guided stereotactic ablative radiotherapy (SABR) for intact prostate cancer – computed tomography (CT) imaging or magnetic resonance imaging (MRI).

SABR is one of the most important advanced radiotherapy techniques currently available for treating tumours. It focuses beams of high-dose radiation at tumour sites with millimetric accuracy – with the aim of achieving local control in just a few short treatments. There is a large body of evidence that SABR treatment given at the right time to the right patient can make a difference to outcomes.

There is now a growing body of evidence supporting extreme hypofractionation – 5 fraction (5#) SABR for patients with low- to intermediate-risk (medium-risk) and selected high-risk localised prostate cancer.

Findings of the MIRAGE trial

Authored by Dr Amar Kishan at the University of California, Los Angeles, a poster presentation at the 2022 American Society of Clinical Oncology (ASCO) Genitourinary (GU) Cancers Symposium showcased the phase III MIRAGE trial2. The focus of the trial highlighted the benefits of MRI-guided treatment over CT-guided treatment in patients receiving the same radiation dose by SABR during prostate cancer treatment.

Patients undergoing SABR for localised prostate cancer were randomly assigned to either CT-guided or MRI-guided treatment. Planning margins of 4mm for CT-arm and 2mm for MRI-arm were positioned around the prostate and proximal seminal vesicles. A dose of 40 Gy was delivered in 5#. For this trial, MR-based adaption was not used. Rectal spacers and elective nodal radiotherapy were allowed at the physicians’ discretion.

The preliminary outcome was the incidence of acute (within 90 days of SABR) grade ≥2 genitourinary (GU) physician-reported toxicity.

Of the 100 patients eligible for evaluation, the interim analysis (51 CT arm, 49 MRI arm) showed that:

  • Acute grade ≥2 GU toxicity was significantly reduced in men receiving MRI-guided SABR (incidence of 24 (47.1%) vs 11 (22.4%), p = 0.01)
  • Acute grade ≥2 gastrointestinal (GI) toxicity was also significantly reduced in men receiving MRI-guided SABR (incidence of 7 (13.7%) vs 0 (0%), p = 0.01)
  • There was a significant deterioration in IPSS scores from baseline in men receiving CT-guided SABR as opposed to the men receiving MR guided SABR at one month, but no difference at 3 months suggesting patients receiving MR guided SABR had less toxicity and recovered more quickly
  • The reduction in EPIC-26 bowel domain scores was more significant after one month in men receiving CT-guided SABR (median change of -8.3 vs 0, p= 0.03). However, this was not the case after three months (median change of -2.3 vs 0, p = 0.4). This means that men receiving MRI-guided SABR had less bowel upset and recovered more quickly

The authors of this preliminary study theorised the lack of statistical difference in patient-reported urinary and bowel function metrics at three months may be due to effective side effect management. The final analysis for the primary endpoint of this study is expected in the coming months.

The MIRAGE trial builds on earlier evidence supporting MRIgRT for prostate cancer using the Phase II study led by Dr Anna Bruynzeel3. This phase II study investigated early GI and GU toxicity after SABR using MR guidance. Both clinician-reported and patient-reported outcomes were better than historical controls in this well-designed phase 2 study.

Stereotactic ablative radiotherapy for prostate cancer

Our 5# SABR for prostate cancer service is an option available to patients which provides:

  • A suitable alternative to surgery – this non-surgical treatment for prostate cancer is especially relevant for patients with co-morbidities in order to avoid a hospital stay or long waiting times
  • No increase in gastrointestinal or genitourinary side effects compared to 20 fractions
  • A reduction in treatment time and less interruption to the patient’s daily life

The additional benefit of a rectal spacer to help reduce damage to surrounding healthy tissues such as the bowel is offered at no extra cost

GenesisCare is an established provider of specialist SABR treatment. A team of expert clinicians leads our service with extensive experience of this SABR modality for all tumour types, and they oversee a nationwide rapid access pathway.

MRI-guided radiotherapy at GenesisCare

We’re proud to be the first healthcare provider in the UK to introduce the MRIdian – an advanced MR linac. The MRIdian combines a linear accelerator with a high-definition MRI scanner, allowing us to offer magnetic resonance image-guided stereotactic ablative radiotherapy (MRIgRT). MRI-guided radiotherapy improves conventional image-guided radiotherapy (IGRT) by providing improved soft tissue definition without additional radiation exposure through high-quality MR images. This world-class radiotherapy system is available at our centres in Oxford and Cromwell Hospital in London and can be accessed by patients throughout the UK.

The treatment planning system of the MRIdian is clear and intuitive, allowing clinicians to see as they treat – adjusting the beam to allow for movements and anatomical changes and making daily re-contouring of tumour and normal tissues straightforward.

The MRIdian uses a patented split-magnet MR design so that the radiation beam is not distorted by the magnetic field and is at the optimum distance for exceptionally sharp, high dose-rate stereotactic ablative radiotherapy (SABR). The automatic beam gating system tracks the target, and if the target moves outside of the pre-specified gating boundary, the radiation beam automatically stops until the target returns inside the gating boundary. This level of accuracy means that uncertainty is reduced, eliminating the need for large margins around the target.

By capturing MR images of the target many times a second, the MRIdian provides real-time moving images that capture the anatomical positional changes that occur naturally within the body.

Find out more about MRI-guided radiotherapy, including case studies and how to refer.

Rectal spacers for CT-guided SABR for prostate cancer

For patients unsuitable for MRI-based imaging, conventional CT image-guided radiotherapy is offered across our network of centres in the UK with the inclusion of rectal spacers.

Rectal spacers are a game-changer in reducing the effects of toxicity to healthy tissues such as the bowel. The spacer is inserted between the rectum and the prostate under local anaesthetic before radiotherapy treatment begins to temporarily move the anterior rectal wall further away from the prostate. This helps reduce the amount of radiation delivered to the rectum and limits toxicity, therefore reducing bowel, urinary and sexual function related side effects.

Who can I refer for SABR for prostate cancer at GenesisCare?

If you wish to refer a patient for 5# SABR for primary prostate cancer on either a conventional linac or the MRIdian MR linac, the eligibility criteria is as follows:

  • Biopsy proven adenocarcinoma prostate, Gleason ≥ 6
  • T-Stage: T1c-T3b
  • No evidence of lymph nodes or distant metastases
  • Prostate volume ≤ 90 cc
  • IPSS ≤ 19
  • No TURP within eight weeks
  • No artificial hips (these are only suitable for treatment on the MR linac)
  • No inflammatory bowel disease

Refer a patient

0808 156 9565
0808 156 9565

We invite consultants to contact us to refer to one of our specialists or to find out how we can help you and your patients.


If you have practicing privileges, please complete our comprehensive online referral form and we will process your referral immediately.

If you would like help with processing your referral or would like to discuss applying for practising privileges with GenesisCare, please email


  1. Kishan AU, Ma TM, Lamb JM, Casado M, Wilhalme H, Low DA, et al. Magnetic resonance imaging–guided vs Computed Tomography–guided stereotactic body radiotherapy for prostate cancer. JAMA Oncology. 2023
  2. Cision PR Newswire. Interim Findings from MIRAGE Phase III Randomized Trial Signal Superiority of MRIdian® MRI-guidance in Stereotactic Body Radiotherapy (SBRT) for Localized Prostate Cancer. [Internet]. 2022 
  3. Bruynzeel AME, Tetar SU, Oei SS, Senan S, Haasbeek CJA, Spoelstra FOB, Piet AHM, Meijnen P, Bakker van der Jagt MAB, Fraikin T, Slotman BJ, van Moorselaar RJA, Lagerwaard FJ. A prospective single-arm phase II study of stereotactic magnetic-resonance-guided adaptive radiotherapy for prostate cancer: Early toxicity results. International Journal of Radiation Oncology Biology Physics. 2019;105(5):1086-1094. 
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