Pencil-beam proton therapy is one of best options for targeting and irradiating tumors while sparing healthy surrounding tissue, but the treatment is typically administered five days a week over 25 to 30 days, making it inconvenient for patients.

In a new randomized trial, researchers at Mayo Clinic say that the therapy could still be effective and have limited side effects in patients with breast cancer if applied in a condensed 15-day hypofractionated schedule, with the dosage increased in sessions, reducing an entire course to three weeks.

They found that the shorter therapy demonstrated excellent cancer control, spared normal tissue, and was comparable in side effects to the longer schedule. Theirs is the first prospective study that supports using shorter-course proton postmastectomy radiotherapy, including for patients who receive immediate breast reconstruction, and the first to show mature results in a randomized trial for breast particle therapy.

"Ultimately, our goal is to personalize radiotherapy based on tumor biology. We want to identify the best possible radiotherapy schedules or drug-radiotherapy combinations to eliminate cancer while minimizing side effects,” said Dr. Robert Mutter, a radiation oncologist and physician-scientist at Mayo Clinic Comprehensive Cancer Center, in a statement.

While proton therapy is associated with minimal side effects compared to photon radiation, access is limited by the small number of proton centers worldwide and the expenses associated with the therapy.

Mutter says that the shorter course’s safety and feasibility could help open up access to proton therapy for patients with difficult-to-treat breast cancers. He and his colleagues plan to investigate optimizing and applying PMRT in just five days.

The findings were published in The Lancet Oncology.

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