Oct. 21, 2025
While radiation therapy has been an effective treatment for patients with many types of cancer, the process of receiving treatment — which could include up to 44 sessions delivered over nine weeks — is prohibitive for many patients.
Now, a new phase 3 trial led by Carlos E. Vargas, M.D., has demonstrated that higher doses of proton therapy delivered over fewer sessions can be just as effective, with equivalent toxicity, in treating prostate cancer. Dr. Vargas is a radiation oncologist at Mayo Clinic Comprehensive Cancer Center in Arizona.
Commitment to patient centricity
Stereotactic body proton therapy (SBPT) relies on high doses of proton radiation delivered with high precision to localized areas to treat cancer. More traditional forms of radiation therapy, such as intensity-modulated radiation therapy (IMRT), don't hold the same precision or fractional standards.
The standard dose fractionation for proton therapy has been 45 treatments given over nine weeks, which, while effective, makes it challenging for patients to receive care, especially since many patients need to travel to have access to proton therapy and must take significant time away from their loved ones, homes and careers.
"In this trial, our goal was to make treatment more patient-friendly but keep comparable outcomes," says Dr. Vargas. "A large proportion of patients at Mayo Clinic come from somewhere else. Shorter treatment time makes it much more accessible for patients to travel for care."
The new study focused on prostate cancer treatment. Over this course, radiologists delivered higher doses of proton therapy over shorter time frames, allowing for fewer treatment sessions. The revised treatment protocol outlined in the study meant delivering treatment over five sessions. Treatment took place on consecutive days or every other day, which reduced the total treatment time from more than two months to less than two weeks.
"This study began more than a decade ago, so for many years we've been able to offer these shorter courses — especially to younger, healthier patients," says Dr. Vargas. "Even if we're not offering five treatments, doing 20 sessions over four weeks for older patients or those with comorbidities is a more patient-friendly approach."
Improving delivery of proton therapy
Proton therapy brought greater power and precision to radiation treatment, enabling oncologists to use fewer beams to reach their target with a lower integral dose to the rest of the body. In the case of prostate cancer care, that meant that most of the dose was restricted to the prostate rather than the areas around it — one of the challenges of X-ray radiation.
"We would need to deliver 45 to 50 treatments of IMRT to give the same biologic equivalent dose we achieve with five sessions of proton therapy," says Dr. Vargas. "This means we are able to deliver a higher biologic dose against the cancer than possible with traditional radiation."
To improve delivery accuracy, physicians use new biologic markers in conjunction with proton therapy. This allows them to be more precise when delivering radiation. As a result, most of the prostate can be preserved, and toxicity to nearby areas is limited. In this study, Dr. Vargas found that toxicity in the rectum and bladder was equivalent to the control group, even while the dosage delivered to the cancer was higher. This leads to a greater biologic effect on the cancer.
"The results showing toxicity is equivalent suggest that the control group of fewer, higher doses was noninferior to the existing standard of care," says Dr. Vargas.
Innovation guides innovation for cancer care
Once Dr. Vargas and his colleagues proved this treatment regimen was safe and effective, they began incorporating it for other indications of cancer. The team is now running a phase 3 trial for five sessions of postprostatectomy radiation therapy. This was not possible previously since there was thought to be no target for radiation once the tumor was removed.
"This treatment approach has been an evolution," says Dr. Vargas. "We had trials before that informed us; then data from this new trial allows us to move forward with radiation therapy treatments for other kinds of cancer, postprostatectomy care and treatment for patients with high-risk prostate cancer."
At every step, the drive for patient-centric care informs the next steps in innovation for this cancer treatment.
"Often, the standard of care for advanced prostate cancers includes systemic therapy that may decline quality of life. Now, we have new options that can limit that," says Dr. Vargas. "We are always working toward a more patient-friendly, personalized approach in our cancer program at Mayo Clinic."
This approach includes a team-based model at Mayo Clinic's Proton Beam Therapy Program, which includes physicists, physicians and therapists who work together on each patient's personalized treatment plan. It also means a commitment to building on past innovations in ways that support patients.
"The way we are doing treatments at our proton center is far more sophisticated than how we did them in the past," says Dr. Vargas. "We can now deliver even more-targeted treatments with higher precision — advancements that were not available during the original trial. Yet, we still achieved amazing results and are continuing to build on them to benefit our patients."
For more information
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