Two larger doses of radiotherapy for prostate cancer caused no additional side effects compared to the standard five doses of radiotherapy, according to results from the HERMES trial presented at the Congress of the European Society for Radiotherapy and Oncology (ESTRO 2026). Experts say the research brings the field one step closer to safe and effective radiotherapy in only two outpatient sessions.
The HERMES study, one of the first to randomly assign patients to either two or five radiotherapy sessions, was presented by Sian Cooper, MBBS, a clinical research fellow at The Royal Marsden NHS Foundation Trust and the Institute of Cancer Research in London.
She said, “Radiotherapy is one of the main treatments used to cure prostate cancer. The current standard of care in many countries for localized prostate cancer is five radiotherapy sessions. Over recent years, there has been a move to deliver radiotherapy in fewer sessions, with a larger dose each session. For patients, a two-session treatment course would be far less disruptive than the weeks of daily hospital visits that radiotherapy has traditionally required. This convenience comes with clear benefits for work, leisure, family life, and travel. For clinicians and health systems, fewer fractions mean faster workflow throughput and getting patients the right treatment, quicker.”
“We wanted to find out whether giving the equivalent dose in just two treatment sessions could be feasible and safe for patients, and to understand how it might affect the potential side effects patients can experience, such as problems with urinary and bowel function,” Dr. Cooper concluded.
Study Details and Results
The team recruited 46 patients with prostate cancer; 24 patients were treated with the standard five doses of radiotherapy over 2 weeks, and 22 patients were treated with the equivalent dose—but in just two sessions over 8 days.
Treatment was delivered using magnetic resonance imaging (MRI)-guided adaptive radiotherapy, allowing exceptional precision in targeting the prostate while protecting surrounding healthy tissue.
The team found that two sessions of radiotherapy using MRI-guided technology was safe and feasible and that condensing the treatment plan into fewer doses had no impact on the side effects that patients experienced.
Dr. Cooper explained: “Around one in four patients in both groups experienced moderate urinary side effects, such as increased frequency or urgency at any point between 6 months and 2 years after treatment. There were no severe urinary or bowel side effects seen in either group. Bowel side effects were very low, with no patients in the two-session group reporting bowel side effects. After 2 years, our patients reported minimal change in their quality of life. There was no difference or minimal difference in the side effects experienced by the patients in the two-dose group compared to the standard five-dose group.”
Expert Commentary
ESTRO President Matthias Guckenberger, MD, of University Hospital Zurich, Switzerland, who was not involved in the research, added: “Radiotherapy is one of the main ways we can treat and cure prostate cancer. It is noninvasive, minimizes the risk of damage to the bladder, and preserves sexual function. Until recently, it was thought that delivering multiple treatments over a longer period was most effective. This study suggests that delivering patients’ treatment in fewer higher doses is both effective in treating the cancer and has minimal impact on the side effects that patients might experience.”
“Limiting treatment to two doses is more convenient for patients, who would need fewer hospital visits, making it easier for those who live far from radiotherapy centers to complete their treatment. It is reassuring for patients to know that potential side effects are not affected by a more condensed treatment plan. It can also reduce the associated costs for hospitals and treatment centers.”
“While the technology used in this trial is currently available in only a limited number of specialist centers worldwide, they are growing rapidly. These results can help guide how they are used and help us understand whether two-session radiotherapy should become a new standard of care,” he concluded.
DISCLOSURE: For full disclosures of the study authors, visit estro.org.
