Single-fraction SBRT ‘a one-stop, knockout punch’ for oligometastatic lung tumors
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Single-fraction stereotactic body radiation therapy appeared safe and effective for patients with up to three oligometastatic lung tumors, according to results of the phase 2 SAFRON II trial presented at the virtual ASTRO Annual Meeting.
“Single-fraction [SBRT] may be considered a one-stop, knockout punch type of approach for patients with one to three metastases to the lung,” Shankar Siva, PhD, associate professor of radiation oncology and head of the SBRT program at Peter MacCallum Cancer Center in Melbourne, said during a press conference. “The lung is the second most common place for cancer to spread, with most patients treated with lifelong cancer therapy only, with little prospect for long-term cancer control. Some patients may have limited spread to the lungs and may be suitable for invasive surgery or noninvasive [SBRT] with the aim of providing long-term cancer control.”
Siva and colleagues evaluated two schedules of SBRT — a single fraction dosed at 28 Gy and four fractions dosed at 12 Gy each— among 90 patients with one to three lung metastases from primary tumors of other sites (47% colorectal, 11% lung, 10% kidney).
Severe treatment-related toxicity at 1 year served as the primary endpoint.
The safety analyses included 37 patients in each group who were eligible for evaluation 1 year after treatment.
Grade 3 or higher treatment-associated adverse events within 1 year occurred among 5% of patients in the single-fraction group and 3% of those assigned to the four-fraction group.
Two patients in the single-fraction group experienced grade 3 adverse events that lasted less than 3 months, including fatigue, loss of breath and chest pain, with no grade 4 or grade 5 adverse events in that group. In the four-fraction group, one patient with underlying interstitial lung disease experienced grade 5 pneumonitis within 3 months of radiation therapy; however, no grade 3 or grade 4 adverse events occurred.
Researchers additionally compared local control, OS and DFS rates between the two groups. They reported local control rates of 93% (95% CI, 79-98) in the single-fraction group vs. 95% (95% CI, 81-99) in the four-fraction group, OS rates of 95% (95% CI, 83-99) vs. 93% (95% CI, 80-98) and DFS rates of 59% (95% CI, 43-72) vs. 60% (95% CI, 44-73).
“Both single-fraction and four-fraction [SBRT] have acceptable toxicity profiles for patients who have one to three secondary cancer deposits to the lung,” Siva said. “The oncologic outcomes from both approaches appear similar at 1 year at this point. Single-session [SBRT] is safe, convenient and appears effective to date for lung secondaries. These findings may have implications for treatment selection in resource-constrained environments, such as [during] the current global COVID-19 pandemic, and is quite a convenient approach for patients.”
Perspective
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Edward S. Kim, MD, MBA, FACP, FASCO
SBRT has found many uses in the management of patients with cancer, especially lung cancer. As treatment of oligometastatic disease becomes more the norm for patients who are either on surveillance or maintenance therapy, the strategy has improved outcomes. The phase 2 SAFRON 2 study demonstrated that single-fraction radiotherapy has similar outcomes as four fractions of radiotherapy. The study results do not substitute SBRT for surgical resection, as the study population comprised those with metastatic disease in which their systemic disease was controlled and who had one to three tumors in the lung.
As treatment de-escalation is accelerated in the precision medicine era, the same must apply to invasive procedures. Less systemic therapy leads to fewer overall side effects and allows for continued and additional treatments for patients. Strategies forthcoming will include delivering radiation in combination with other targeted therapies and immunotherapies. Continued testing of less intensive but similarly effective therapy will allow further investigation and less toxicity for patients.
Perspective
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Gregory M.M. Videtic, MD, CM, FRCPC
This study is important and relevant for a number of reasons. It adds to the growing portfolio of prospective randomized studies in the still-evolving discipline of lung SBRT. Notwithstanding the challenges in carrying out long-term studies in radiation oncology, the authors successfully completed this multi-institutional study, which provides additional understanding of lung SBRT’s safety as well as its efficacy.
Next, the use of single-fraction lung SBRT in this study complements the data that have already accrued from the medically inoperable early-stage lung cancer population. Long-term results from two randomized phase 2 studies in this population showed that a single fraction of lung SBRT is as effective as multi-fractionated SBRT when it comes to safety, local control and OS. This is why some clinicians now consider single-fraction acts as the standard of care for peripheral curable inoperable lung cancer.
Lastly, it confirmed that disease outcomes for patients with limited oligometastases are safely and effectively achievable with this approach.
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Siva S, et al. Abstract 5. Presented at: American Society for Radiation Oncology Annual Meeting (virtual); Oct. 25-28, 2020.
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