Under what conditions would you offer observation for asymptomatic low volume brain metastases?

This is becoming an increasingly more common scenario with patients undergoing routine brain MR for staging, even in the absence of symptoms, and also, with a very modestly small number of settings demonstrating excellent radiographic responses to targeted agent or immune checkpoint inhibitors (ICI). So, let us review where withholding radiotherapy (aka observation, since systemic therapy will likely not be withheld) is a possible consideration:

1. When the diagnosis is in doubt and short interval follow-up imaging is being considered to determine the diagnosis with more certainty.

2. When the patient's prognosis is otherwise very grim, with very short life-expectancy from other disease processes such that metastatic progression in the brain ...