Prostate cancer is the most commonly diagnosed cancer in men, affecting nearly 300,000 families in the United States each year. For those with localized disease, treatment decisions can be challenging and personal. One study found that about 55% of men choose surgery, 32% choose radiation therapy, and 13% choose active surveillance.1-2
Radiation therapy can be delivered in several ways, including external beam radiation therapy, stereotactic body radiation therapy (SBRT), and brachytherapy. Traditional external beam therapy can range from 20 to 45 daily treatments, while SBRT condenses treatment into just five sessions or fewer, delivering higher doses each time. Studies have shown SBRT to be as effective as longer regimens, with the added benefit of saving patients weeks of daily visits.
Benefit of MRI guidance
Technological advances have greatly improved how radiation is delivered. The development of the magnetic resonance imaging linear accelerator (MRI-linac) combines the high-contrast imaging of MRI with the precision of a modern radiation therapy machine.
MRI offers improved visualization of soft tissues compared with CT scans, allowing doctors to see and better delineate the prostate and surrounding organs. This means radiation can be targeted more precisely to the tumor, while sparing nearby structures such as the bladder and rectum. MRI can even allow visualization of dominant intraprostatic lesions, which, when targeted and treated, can improve disease control.³
Adapting treatment in real time
Another benefit of MRI guidance is the ability to adapt treatment in real time. Before each daily fraction, a new MRI scan is performed. If the prostate or surrounding anatomy has shifted due to bladder filling or rectal changes, the plan can be adjusted on the spot while the patient is on the table to better treat the prostate and avoid normal organs.
During treatment, continuous MRI monitoring tracks the prostate. If the prostate moves out of position, the machine automatically pauses. The care team can then adjust the patient's position or further adapt the treatment plan to account for any anatomic changes. This prevents unintended radiation from being delivered to normal organs, further reducing treatment toxicity. In standard CT-based treatments, these anatomic changes would not be detected because there is no live imaging, possibly resulting in the dose being delivered to normal organs.
Evidence from the MIRAGE trial
The clinical benefits of MRI guidance were tested in the MIRAGE trial, a phase 3 randomized study comparing MRI-guided SBRT with CT-guided SBRT in men with localized prostate cancer.⁴
Key findings showed an improvement in both acute and late side effects:
- Acute side effects: MRI guidance significantly reduced grade 2 or higher urinary toxicity (24.4% vs. 43.4%) and gastrointestinal toxicity (0% vs. 10.5%).⁴
- Late side effects: MRI guidance lowered the incidence of grade 2 or higher urinary toxicity (27% vs. 51%) and gastrointestinal toxicity (1.4% vs. 9.5%).⁵
These results demonstrate that MRI-guided therapy can translate into meaningful reductions in both short- and long-term treatment-related toxicities in men who choose radiation therapy for their prostate cancer.
Looking ahead
MRI-guided radiation represents a new frontier in prostate cancer care. By combining real-time imaging, adaptive planning, and precision targeting, MRI-guided therapy offers the potential for safer treatment with fewer side effects and less disruption to daily life.
As Prostate Cancer Awareness Month reminds us, progress is not only about curing disease — it is about ensuring men can live well during and after treatment. Current and future research will continue to pursue the goal of improving therapy with shorter and more convenient treatments, improved outcomes, and lower toxicity.
Learn more about prostate cancer care available at Northside.
References:
- American Cancer Society. “Key Statistics for Prostate Cancer.” American Cancer Society. Accessed September 2025. https://www.cancer.org/cancer/types/prostate-cancer/about/key-statistics.html.
- Wallis, Christopher J. D., et al. “Association of Treatment Modality, Functional Outcomes, and Baseline Characteristics With Treatment-Related Regret Among Men With Localized Prostate Cancer.” JAMA Oncology 8, no. 1 (2022): 50–59. https://doi.org/10.1001/jamaoncol.2021.5160.
- Kerkmeijer, L. G. W., et al. “Focal Boost to the Intraprostatic Tumor in External Beam Radiotherapy for Patients With Localized Prostate Cancer: Results From the FLAME Randomized Phase III Trial.” Journal of Clinical Oncology 39, no. 7 (March 1, 2021): 787–96. https://doi.org/10.1200/JCO.20.02873.
- Kishan, Amar U., et al. “Magnetic Resonance Imaging–Guided vs Computed Tomography–Guided Stereotactic Body Radiotherapy for Prostate Cancer: The MIRAGE Randomized Clinical Trial.” JAMA Oncology 9, no. 3 (March 1, 2023): 365–73. https://doi.org/10.1001/jamaoncol.2022.6558.
- Kishan, Amar U., et al. “Magnetic Resonance Imaging Versus Computed Tomography Guidance for Stereotactic Body Radiotherapy in Prostate Cancer: 2-Year Outcomes From the MIRAGE Randomized Clinical Trial.” European Urology 87, no. 6 (2025): 622–25.
