Steroid treatment for brain edema to be replaced by Boswellia.

Have brain edema after SRS(Cyberknife) treatment for meningioma. The neurologist prescribed steroids to defeat the edema. The now larger edema seems to be stabilized but not inclined to reduce in size. The neurologist now wants to prescribe a herbal extract called Boswellia to supplement the steroids initially then eventually to replace the steroids.
Has anyone gone through thi treatment? What are your results/opinions.
Also, because it is a herbal extract not covered by the FDA, how did you find a a trustworthy source. Our neurologist would not provide a source recommendation.