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FLASH radiation therapy shows promise in first human trial


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FLASH radiation therapy – delivering a therapeutic dose of radiation in a fraction of a second – holds promise as a potential treatment for hard-to-kill tumours, a first human study in a small number of people. people with bone cancer showed. The technology, which has previously been tested on animals, has been shown to be safe and appears to be as effective as conventional radiation without causing unwanted side effects. The results of the FAST-01 trial (NCT04592887) will be presented today at the American Society of Radiation Oncology (ASTRO) Annual Meeting.

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

FLASH radiation therapy (RT) delivers radiation at a dose rate 300 times higher than that used in conventional radiation treatments. This creates a phenomenon known as the FLASH effect, which reduces the possible harm to normal tissue surrounding the tumor during conventional radiation therapy, while still killing cancer cells at the tumor site.

“Because FLASH radiation therapy is delivered at an extremely high dose rate, it appears to cause less damage to normal tissue. This offers the ability to deliver a larger dose of radiation – which can lead to higher cure rates for patients with drug-resistant tumors – without the increased side effects John Breneman, MD, FASTRO, trial principal investigator and professor of radiation oncology and neurosurgery at the University of Cincinnati Cancer Center.

Most of the early research on FLASH RT used electron beams to deliver radiation, but these beams did not penetrate deep into the tissue, limiting its applicability for this treatment. Using proton beams for extremely high dose rate radiation allows for sufficient penetration to reach tumor sites in most people. While preclinical animal trials have shown that FLASH-RT can safely deliver high doses of radiation with fewer harmful side effects, prior to the FAST-01 trial, this treatment was has not been clinically tested in humans.

In this study, ultra-high-dose rate radiation was administered to 10 patients, ages 27-81, each with one to three painful bone metastases in their extremities. The treatments were delivered to 12 cumulative metastatic sites in the patient’s arms and legs. The patient was irradiated with 8 Gy radiation in a fraction, delivered at a rate of ≥40 Gy per second through the FLASH-assisted proton therapy system. Pain, analgesic use, and adverse events were measured on the day of treatment, 15 days after treatment, and at one, two, and three months after treatment. The researchers continued to measure these results every two months for up to 13 months. The mean follow-up time was 4.8 months.

The researchers selected patients who would receive conventional radiation therapy at the same dose as they received FLASH RT. Dr. Daugherty said: “We used the exact same regimen, but with FLASH dose-proportional radiation. The patient experience was the same as with conventional radiotherapy, only the course of the treatment was different. shorter”.

According to FLASH RT, seven out of 10 patients had complete or partial pain relief. Of the 12 sites treated, pain was completely relieved in six sites and partially in two additional sites. Temporary pain occurred in four of the 12 treated sites.

The side effects from the treatment are mild. Four patients had mild hyperpigmentation (darkening skin color), one had skin discoloration, two had mild limb edema (swelling or blistering), two had pruritus (itchy skin), one had fatigue, one had erythema (redness of the skin) and one had quadriplegia.

Each FLASH treatment takes about 3/10 seconds, Dr. Daugherty explains. After treatment, “both pain relief and side effects were consistent with what can happen with conventional radiation. We did not see any unexpected additional toxicity with a significantly shorter duration. treatment. “

Dr. Breneman said FLASH RT is likely to be most useful in treating hard-to-kill cancers in the brain, lungs or gastrointestinal tract areas, where healthy tissue around tumors is particularly vulnerable. injury when exposed to radiation. However, clinical trials in these locations are not authorized until studies show that extremely high dose rate radiation is safe and effective in other, less sensitive areas. The FDA limited the approval for this study to adults with bone metastases in the arms and legs, areas where the risk is much lower if complications arise.

“From a practical standpoint, this is not the type of cancer that FLASH was designed to treat, but we needed human data to see if there were any unwanted side effects. and legs are not as dangerous as treating someone’s brain or lungs,” said Dr. Breneman, with whom he is also medical director of Cincinnati Medical Center’s Children’s Proton Therapy/UC Center.

Finally, FLASH RT may also be useful in treating childhood cancer, as children are more sensitive to the side effects of radiation therapy, he said. But more research needs to be done before that can happen.

Dr Daugherty said that researchers still do not fully understand why FLASH RT kills tumors with fewer side effects than conventional radiation, and more research is needed to determine the biological mechanism that produces this effect. FLASH response.

Next, the research team will test the safety and effectiveness of FLASH RT in patients with metastases closer to the lungs and heart. Trial FAST-02 (NCT05524064) is currently enrolling adult patients with thoracic bone metastases.


Cancer treatment without side effects?


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