U.K. research has shown that condensing prostate cancer radiotherapy into two sessions, but with a higher dose per session, rather than the traditional five sessions does not lead to increased side effects when treatment is delivered using state-of-the-art magnetic resonance imaging (MRI)-guided technology.
Lead researcher Sian Cooper, clinical research fellow at The Royal Marsden NHS Foundation Trust and the Institute of Cancer Research in London, told Inside Precision Medicine that the results of the HERMES trial “point toward a future where prostate radiotherapy is tailored to the disease, to the individual’s anatomy and symptom profile, whilst being mindful of the impact of treatment time on patients’ lives.”
Presenting at the 2026 Congress of the European Society for Radiotherapy and Oncology (ESTRO), Cooper said that the number of people diagnosed with prostate cancer is projected to double by 2040, meaning the demand for effective and efficient treatment has never been greater.
At present, localized prostate cancer is typically treated with stereotactic body radiotherapy over five sessions, but there has been increasing interest delivering the treatment 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,” said Cooper.
“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.”
The move toward giving higher radiotherapy doses in fewer sessions has been made possible by improvements in radiotherapy delivery technology over recent years.
“It has allowed us to harness the power of modern computing and discoveries in clinical physics, to create radiotherapy doses which conform very tightly to the edge of the prostate,” Cooper explained. “This results in vastly less dose to the normal, healthy tissues around the cancer.”
The HERMES trial used a Unity MR-Linac (Elekta AB, Sweden) machine, which Cooper describes as “the ultimate evolution of this progress,” to deliver radiotherapy to participants.
The device combines real-time MR scanning with a linear accelerator and is known as MRI-guided adaptive radiotherapy. It allows adaptation of the radiotherapy beam design to changes in patient anatomy on the treatment day as well as moment by moment motion management, meaning that if there are any changes in the target or healthy bystander organs, the radiation beam can be switched off.
“This level of precision was needed to safely deliver the high dose of radiation necessary to maintain the biologically equivalent dose in just two fractions,” Cooper noted.
In all, 46 participants (median age 74 years) with intermediate or lower high-risk prostate cancer were randomly assigned to receive radiotherapy at a dose of 24 Gy in two fractions over 8 days, with a 27 Gy integrated boost to the MRI defined tumor (n=22), or 36.25 Gy in five fractions over two weeks to the planning target volume, with 40 Gy to the prostate and proximal one cm seminal vesicles (n=24). All participants had androgen deprivation treatment for at least six months.
Cooper reported that, at two years, four (18%) participants in the two-fraction arm and six (25%) in the five-fraction arm experienced moderate (grade 2) urinary adverse events (AEs) such as increased frequency or urgency. Grade 2 gastrointestinal AEs occurred in one participant in each arm (5% and 4%, respectively).
There were no grade 3 or worse genitourinary or gastrointestinal events in either group.
The team also showed that quality of life, measured by the International Prostate Symptom Score and the International Index of Erectile Function, showed minimal change up to two years but will continue to be monitored up to five years.
Cooper said that the investigators will present efficacy data, a secondary endpoint, when it matures but she pointed out that as “the cancer control rate for prostate cancer is so high, it often takes many years for failures to appear, whereas trial data for ultra hypofractionation show that the genitourinary adverse event rate is the primary concern after treatment.”
ESTRO president, Matthias Guckenberger, MD, from University Hospital Zurich, Switzerland, who was not involved in the research said: “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.”
The post Ultra-Short Radiotherapy Schedule for Prostate Cancer Supported by HERMES Trial appeared first on Inside Precision Medicine.

