The researchers also compared survival rates between the groups a year after treatment and found them to be nearly identical across both regimens. Local control rates were 93% for patients who received a single SBRT treatment, compared to 95% for those who received four treatments; overall survival rates were 95% and 93%; and disease-free survival rates were 59% and 60%. Dr. Siva said the team will continue to analyze these secondary endpoints up to three years after treatment, as well as quality of life and cost effectiveness.
If proven safe and effective over the long-term, single-fraction SBRT can be an appealing treatment for patients with oligometastatic cancer to the lungs, said Dr. Siva. In addition to clinical benefits, SBRT has practical benefits for patients, such as fewer trips to a clinic, less time off work and lower treatment costs. “The alternative treatments for oligometastatic cancer are ongoing drug therapies with little expectation for long-term control or surgery, which can have difficult side effects. Radiation is non-invasive, and treatment can be delivered in a relatively short time,” said Dr. Siva.
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The COVID-19 pandemic has encouraged greater consideration of shorter-course therapies, as medical institutions look for ways to reduce potential exposure, especially among vulnerable patients with cancer. "In a pandemic, the idea of a single, non-invasive outpatient treatment that doesn't require anesthesia is appealing in the sense of reducing patient time and transmission risk in the clinic," he said.
SBRT is typically spread out over up to five treatment sessions. "When we compress a multi-treatment course into a single treatment, there is a potential risk of higher toxicity. Based on our own anecdotal experience, we are quite comfortable using the single treatment approach, but globally, it's used less often," explained Dr. Siva. "There also are concerns that a single treatment might not have the same kind of effectiveness as multiple treatments. Thankfully, in this study, at least a year out we are seeing similar efficacy, where 93-95% of the tumors were controlled in both arms. Our final analysis will show if this holds for the long-term, but these early results indicate that single fraction radiation could be carried out equally effectively across multiple institutions.”
That the study was conducted across 13 institutions speaks to the general applicability of its findings and the SBRT approach, said Dr. Siva. He also stressed the importance of incorporating quality assurance into its rollout, however. "The safe delivery of SBRT, particularly in a single session, requires a multi-faceted system of quality assurance, peer review and treatment planning. You need to be absolutely certain of the accuracy of your treatment delivery, and I think it's very important that treatment teams achieve the same high levels of quality control, to make sure we are achieving the best in cancer care."