Do you need renal biopsy before SBRT for RCC suspicious cancer?

Yes. The teaching is usually that ≈ 20% of small renal masses (<4 cm) are benign, and this rate goes down as size increases (Thompson et al., PMID 19286217). Features such as contrast enhancement, tumor location, and sex can help to improve the malignant risk potential of these lesions, but no combination of factors can conclusively predict for malignancy as reported in a prior systematic review.

Given this and drawing from basic principles of radiation oncology, I am hesitant to offer RT withou...

Interesting question. In the IROCK metaanalysis, 83% of the patients had pathological confirmation. So not everyone requires a biopsy although it is recommended. In cases like this, one can weigh the pros and cons of upfront SABR to the renal mass versus short-term surveillance, especially with a competing risk factor such as HCC. Factors that could influence this decision are size and previous growth. A small renal mass with minimal previous growth may not justify immediate intervention, howeve...

Rare case to not have or be able to do a biopsy (usually there is significant co-morbidity so makes you question the benefit to the planned radiation therapy). In this case, you mention HCC which would likely need to be treated first as it is likely the more problematic cancer (although there is some systemic therapy overlap should a patient have immunotherapy and/or VEGF inhibitor therapy)

Not usually. If the patient comes with a Bx then fine now I don't. Surgeons routinely take these patients to the OR without a Bx. For us community docs, we don't all have reliable expeditious IR for Bx. I've treated about 120 SBRT kidneys. Morbidity is so low. What is the false negative rate of Bx in a small renal lesion in an old patient on anticoagulation?