SRS FOR BRAIN METASTASES

Management of brain metastases has been evolving over the past decade, with increasing use of stereotactic radiosurgery (SRS). Some experts argue that it should replace whole brain radiation therapy (WBRT) as the standard of care.

However, while SRS has been growing in popularity, guidelines for SRS remain somewhat limited. In particular, there appears to be no consensus on the optimal treatment strategy for patients with more than three brain lesions, and practice patterns vary considerably, researchers write in a paper published online in Cancer.

Among surveyed radiation oncologists who were given hypothetical scenarios, responses for the number of lesions requiring a switch from SRS to WBRT depended on physician characteristics.

Central nervous system (CNS) specialists were consistently more likely to treat more metastases with SRS. Their "cutoff number" for making a switch from SRS to WBRT was significantly higher than that of non-CNS specialists (8.1 vs 5.1 among high-volume providers).

Patient volume also played a role. CNS specialists who treated higher numbers of patients with brain metastases also reported a significantly higher cutoff number compared with those treating a lower volume of patients (8.1 in high-volume providers vs 5.6 in low-volume and 4.1 in minimal-volume providers).

"When we surveyed radiation oncologists, we had a feeling that this is what we would see," said lead author, Percy Lee, MD, an associate professor and vice chair of education for the Department of Radiation Oncology at the David Geffen School of Medicine at UCLA and the UCLA Jonsson Comprehensive Cancer Center, California.

"This is an area with a lot of controversy but not with a lot of evidence one way or another," Dr Lee told Medscape Medical News. "My take-home message is we need more solid clinical evidence to help guide decision making."

He pointed out that current published guidelines are detailed and instructive for patients who have up to three or even four brain metastases. But as SRS techniques improved and providers became more skilled with the technology, higher numbers of brain metastases are being treated with SRS.

Consensus guidelines, such as those published by the National Comprehensive Cancer Network, are limited in scope; instead, the choice of SRS or WBRT is often at the discretion of the clinician.

This lack of evidence is problematic, explained Dr Lee. "We have evidence to support SRS for three brain metastases, but what about four or five? There is no clear evidence either way.

"It is dangerous to have a cutoff number when it is not evidence based," he said.

WBRT or SRS?

There has been growing controversy over the use of WBRT and whether SRS — which many providers see as more precise, less toxic, and more convenient — can replace it, at least for patients without an extensive number of lesions.

The first randomized trial comparing SRS to WBRT produced mixed results: Overall survival was the same, but both methods had pros and cons. SRS, for example, provided patients with better cognitive outcomes, but WBRT was superior for the local control of the brain metastases

As part of their second "Choosing Wisely" campaign, the American Society for Radiation Oncology (ASTRO) recommended that oncologists should not routinely add adjuvant WBRT to SRS for limited brain metastases because for most of these patients SRS alone is sufficient.

For patients with brain metastases from solid tumors who have good performance status, data from randomized studies show no overall survival benefit from the addition of adjuvant WBRT to SRS. Instead, these data indicate that the addition of WBRT to SRS is associated with diminished cognitive function and worse patient-reported fatigue and quality of life.

However, the ASTRO statement did not specifically give a cutoff number for presenting lesions, and some experts said that the vagueness and omitting a number opens up SRS for use in a wide range of patients.

"There is good reason to try to avoid WBRT, but maybe now technology has advanced to where we can safely deliver radiotherapy to seven brain metastases," said Dr Lee. "Maybe 10 years ago people were uncomfortable with that, but if you can prove it's safe and not going to compromise outcomes, why not, if it can save cognitive function? That is the rationale, but we don't have guidelines for this."

Variety in Practice

In this study, Dr Lee and colleagues looked at clinicians' practice patterns for use of SRS in the treatment of brain metastases.

A total of 711 practicing radiation oncologists responded to the survey, which asked them to identify an ideal "cutoff number" for when they would switch from using SRS to using WBRT.

The survey also asked questions about which patient cohort presented the greatest challenge to treat.

Respondents were presented with a series of clinical scenarios involving patients with brain metastases, and they were asked to select an option for management. For example, in one scenario, they were asked how they would treat a newly diagnosed patient with lesions measuring?less than?3?cm in size and with a primary tumor that was not of small cell, leukemia, lymphoma, or germ cell histology.

CNS specialists were more likely to choose SRS or a combination of SRS and WBRT compared with non-CNS specialists.

Dr Lee and his team also found a trend between the cutoff number and patient volume treated per month, but this was true only among the CNS specialists. The difference in the cutoff number between high-volume specialists and nonspecialists reached statistical significance (P??.001), but the type of practice (academic vs nonacademic) did not appear to influence the cutoff number.

Another question posed to respondents was to rank what they considered to be the most important factors in choosing between WBRT and SRS for patients with newly diagnosed brain metastases. The "number of lesions" was the top choice as the most important factor, and "convenience to the patient" was selected as the least important.

Providers were also asked to select the group of patients that they found to be the most challenging when making treatment decisions. A majority (342 respondents [56%]) chose patients with four to six metastases, while the second most selected group (107 respondents [17%]) consisted of patients with seven to nine metastases.

When the responses were compared between academic vs nonacademic providers, CNS specialists vs non-CNS specialists, and high-volume practice vs low-volume practice and minimal volume practice respondents, no significant differences were noted between groups.

Dr Lee pointed out that some patients who receive SRS do need to have WBRT eventually. "So we need to look and see how this can be avoided in patients who were treated for more than three lesions," he said. "Maybe there is certain histology or patient factors, or biomarkers, that may be able to tell us about the risk of brain metastases."

"That would be very helpful," he added. "And if a patient has a marker for being at high risk, then whole brain radiation is the right solution. We need something more helpful than just a number — in this day and age, that is very archaic."

No specific funding was disclosed. The authors have disclosed no relevant financial relationships.

Cancer. Published online February 8, 2017