ASTRO: New hopes for ultra-high dose radiation

In a small study of patients with metastatic cancer, the treatment — which delivers high therapeutic doses of radiation in a fraction of a second — was found to be as safe and effective for pain relief as traditional radiation, without causing any unexpected side effects.

“It deserves further research because of its potential to reduce the side effects of conventional radiation treatments,” said lead author Dr. Emily Daugherty, assistant professor of clinical radiation oncology at the University of Cincinnati Cancer Center, in a statement.

Flash radiation therapy delivers radiation at dose rates more than 300 times higher than conventional radiation treatment. The technique has the potential to achieve higher cure rates in patients with resistant tumors than in patients receiving conventional treatment, while sparing normal tissue. Initial preclinical animal data suggest that flash radiotherapy produces less toxicity to normal tissues.

Most of the early research into flash radiotherapy used electron beams to deliver the radiation, but the rays do not penetrate very deeply into tissue, limiting the method’s applicability. However, using proton beams for ultra-high dose rate radiation allows for sufficient penetration to reach tumor sites in most people, the researchers found.

In the FeAsibility Study of Flash therapy for the Treatment of Symptomatic Bone Metastases (FAST-01), 10 patients aged 27 to 81 years, each with one to three painful bone metastases in their extremities, were given ultra high dose radiation. Treatments were administered to a total of 12 metastatic sites in the patients’ arms and legs. According to the researchers, the patients received 8 Gy of radiation in a single fraction delivered at greater than or equal to 40 Gy per second via a flash-enabled proton therapy system (Varian Medical Systems).

Pain, analgesic use, and side effects were measured on the day of treatment; 15 days after treatment; and one, two, and three months after treatment. Researchers continued to measure results every two months for up to 13 months. The median follow-up time was 4.8 months.

After flash radiotherapy, seven of the 10 patients experienced complete or partial pain relief. Of the 12 sites treated, pain was completely relieved in six sites and partially relieved in two other sites. Transient bouts of pain occurred at four of the 12 sites treated.

Adverse reactions to treatment were classified as mild: skin hyperpigmentation (G1, n=4), skin discoloration (G1, n=1), limb edema (G1, n=2), pruritus (G1, n=2), fatigue (G1, n= 1), erythema (G1, n=1), and body pain (G2, n=1).

“We found no unexpected additional toxicity with the much shorter treatment,” said Daugherty.

Researchers say the results support further exploration of flash radiation treatments for other clinical indications, including pediatric cancers, because children are more sensitive to the side effects of radiation therapy. But before that can happen, much more research needs to be done.

While flash radiation therapy could be very useful in the treatment of hard-to-kill cancers of the brain, lungs, or gastrointestinal tract, clinical trials involving these sites cannot be approved until studies show that ultra-high dose rate radiation safe and effective in other, less sensitive areas, according to Daugherty et al.

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