ASTRO: Targeted radiation cuts local recurrence of brain metastases, but other outcomes measures not as impressive

BOSTON—If given the chance to choose between two recurrence-busting radiotherapy methods, many patients who have had a metastatic tumor resected from their brain would likely choose finely targeted stereotactic radiosurgery (SRS) applied only to the surgical bed of the resected lesion over radiation therapy applied to the entire brain.

After all, the latter approach (WBRT, for whole-brain radiation therapy) risks damaging considerably more healthy brain tissue and, in the process, causing marked cognitive decline.

These patients may now want to re-think that choice as not exactly a no-brainer: A new study shows that, compared to observation alone, SRS does indeed excel at thwarting local recurrence—but it doesn’t improve rates of overall survival or metastasis to other parts of the brain or body.

Moreover, it appears that smaller tumors “may not need post-operative radiosurgery after resection, since the local failure rate for tumors smaller than 2.5 centimeters was very low,” report the researchers behind the findings.

Lead author Anita Mahajan, MD, professor of radiation oncology at MD Anderson Cancer Center in Houston, presented the research Sept. 25 at the annual meeting of the American Society for Radiation Oncology (ASTRO) in Boston.

Mahajan said study participants included 128 patients (median age, 59) with one to three metastatic brain tumors who wished to avoid or delay WBRT following complete surgical resection of at least one brain metastasis.

Patients were randomly assigned to one of two arms. There were 63 patients who had SRS to the surgical cavity (or cavities, for patients with more than one lesion removed) and 65 patients who received observation alone.

A neuroradiologist assessed failure of local control—the primary endpoint of the study—through follow-up MRI, the aim being to determine whether local tumors recurred in the area treated with SRS.

Researchers also examined the rates of overall survival, development of distant brain metastases, time to WBRT and complications following SRS.

Radiosurgery to the surgical bed significantly reduced local recurrence of the resected tumor, Mahajan said, reporting that, at six months following treatment, local control rates were 83 percent for the SRS group and 57 percent for the observation-alone group.

At the 12-month follow-up, the local control rates were 72 percent for the SRS group, compared to 45 percent for the observation-alone group.

However, at 12 months after treatment, 58 percent of the SRS patients had developed distant brain metastases, compared to 67 percent in the OBS group, although the difference was statistically non-significant (hazard ratio, 0.79; p = 0.29).

Meanwhile, median overall survival was 17 months for both groups.

WBRT was given to 24 of the 64 patients in the SRS group, who had no significant complications, within an average timeframe of 16.1 months. This was statistically similar to the 30 of 67 patients in the OBS group who received WBRT within an average timeframe of 15.2 months.

In terms of non-treatment factors, only tumor size impacted local control, the researchers found. A pre-surgery tumor size of greater than three centimeters was associated with worse local control, they found, but local recurrence “was not significantly affected by the number of brain metastases or the patients’ histology or graded prognosis assessments.” 

“Our research shows that radiosurgery in this patient cohort does reduce the incidence of local recurrence,” Mahajan said, “although the findings for overall brain control, overall survival and time until whole brain radiation therapy limit our ability to conclude an obvious clinical benefit."