Bone cancer FLASH therapy. Representational photo.

In first human trial, FLASH radiotherapy shows promise

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The method was previously tested on animals and was shown to be equally safe and effective without producing unforeseen adverse effects. Today at the annual meeting of the American Society for Radiation Oncology (ASTRO), the results of the FAST-01 trial (NCT04592887) will be discussed.

“Our study shows that proton FLASH radiation therapy is a practical modality for reducing pain,” said Emily C. Daugherty, MD, lead study author and assistant professor of clinical radiation oncology at the University of Cincinnati Cancer Center. . “It deserves further exploration because of its potential to decrease the side effects associated with conventional radiation treatments.”

Compared to traditional radiation treatments, FLASH radiation therapy (RT) delivers radiation at dose rates that are more than 300 times higher. This causes a phenomenon known as the FLASH effect, which reduces the damage that conventional radiotherapy can cause to healthy tissue surrounding a tumor, while at the same time destroying cancer cells at the location of the tumor.

“Because FLASH radiation therapy is delivered at ultra-high dose rates, it appears to cause less damage to normal tissue. This offers the potential to deliver larger doses of radiation, which could result in higher cure rates for patients with tumors.” resistant, without increasing side effects,” said John Breneman, MD, FASTRO, principal investigator of the trial and professor of radiation oncology and neurosurgery at the University of Cincinnati Cancer Center.

Since electron beams do not penetrate very deeply into tissue, they have been used primarily in early FLASH RT studies, which restricted their usefulness for this therapeutic strategy. Proton beams can penetrate far enough to reach tumor sites in most patients when used for ultrahigh-dose-rate radiation. FLASH-RT had never been evaluated in a human clinical study prior to the FAST-01 trial, despite preclinical animal studies suggesting that it could deliver high doses of radiation safely and with fewer adverse side effects.

In this study, 10 patients with one to three painful bone metastases in the extremities, ages 27 to 81, received ultra-high-dose-rate radiation. A total of 12 metastatic sites in the patient’s arms and legs received treatment. Patients received 8 Gy of radiation in a single fraction, delivered via a FLASH-enabled proton therapy device at a rate of approximately 40 Gy per second. On the day of treatment, 15 days later, and one, two, and three months later, pain, analgesic use, and adverse events were recorded. For up to 13 months, the researchers checked these results every two months. The follow-up period was on average 4.8 months.

The researchers chose patients who would have received conventional radiation therapy at the same dose as they received with FLASH RT. “We use the exact same regimen, but with FLASH dose rate radiation. The patient experience is the same as if they had received conventional radiation, only the treatment delivery process is shorter,” said Dr. Daugherty.

After FLASH RT, seven of the 10 patients experienced complete or partial pain relief. Of the 12 treated sites, pain was completely relieved at six sites and partially relieved at two additional sites. Temporary flare-ups of pain occurred at four of the 12 treated sites.

Side effects of treatment were mild. Four patients experienced mild skin hyperpigmentation (darkening of skin tone), one experienced skin discoloration, two experienced mild extremity edema (swelling or swelling), two experienced pruritus (itchy skin), one experienced fatigue , one experienced erythema (redness of the skin) and one experienced pain in the extremities.

Each FLASH treatment takes about 3/10 of a second, Dr. Daugherty explained. After treatment, “both pain relief and side effects were consistent with what might have happened with conventional radiation. We didn’t see any unexpected additional toxicity with the substantially shorter treatment.”

In the brain, lungs, or gastrointestinal tract, where healthy tissue surrounding tumors is more sensitive to radiation exposure, FLASH RT may be more useful in treating hard-to-treat malignancies. However, clinical trials in these locations cannot be approved until research shows that ultrahigh dose rate radiation is safe and efficient in other, less sensitive regions. The FDA only approved this trial for people who had bone metastases in their arms and legs, which are places that are much less likely to experience difficulties.

“From a practical standpoint, this is not the type of cancer that FLASH is designed to treat, but we need human data to see if there are any unexpected side effects. Treating arms and legs is not as risky as treating the brain or lungs of someone,” said Dr. Breneman, who also serves as medical director of the Center for Proton Therapy at Cincinnati Children’s/UC Medical Center.

Since children are more susceptible to the negative effects of radiation therapy, FLASH RT may eventually prove useful in the treatment of pediatric malignancies, according to the researcher. But before that can happen, much more research needs to be done.

Further study is required to identify the biological principles underlying the FLASH effect because it remains unclear why FLASH RT kills cancers with fewer adverse effects than traditional radiation, according to Dr. Daugherty.

This story has been published from a news agency source with no changes to the text.

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