What clinical factors help you to determine whether or not a patient is an appropriate candidate for spine SRS/SBRT in the setting of metastatic disease?

Although there are no right or wrong answers, I think there is the least controversy when using SBRT/SRS for progressive disease after previous conventional/palliative RT or for radio-resistant tumor (melanoma, renal cell carcinoma) in patients with limited systemic disease (oligometastatic). As som...