What institutional recommendations guide the choice between brachytherapy and MR-linac-guided SBRT for locally advanced prostate cancer, given that no large trials have directly compared the two?

There is randomized data demonstrating the superiority of brachytherapy boost over EBRT alone mainly from the well-discussed ASCENDE-RT trial. To my knowledge, there is no such data for SBRT (whether alone or as a boost) in this patient population. So, I do not see how they can be considered equal options from which to choose. The FLAME approach of an SIB boost to the MRI-defined tumor is also supported based on a randomized trial showing superiority to EBRT alone. So, IMO, the dilemma is between brachy boost and FLAME. For this, we sorely need comparative data, preferably from a randomized trial. For me, I discuss with patients and try to help them make an informed choice. Given that I have more personal experience and, therefore, confiden...

ASCENDE-SBRT is currently accruing and will be essential to answering this question.

If a patient is a candidate for both approaches from technical and medical standpoints, I review the potential upsides and drawbacks of each approach and have as much of a shared decision with the patient as possible.

My short answer is: the importance of radiation technique depends on the case.

For a man with a slow-growing, localized-appearing tumor who progresses on active surveillance to having gross EPE or possible SVI, with biopsy showing Gleason 7 disease, maybe a PSA in the 8-15 range, that patient is likely going to do pretty well with ST-ADT + RT. There's less evidence for ST-ADT + brachy mono; sure, you could consider EBRT+ brachy boost, but that might be overkill. EBRT + brachy to avoid ADT is also something to consider.

Contrast that with a guy who presents with focal EPE but Gleason 9 in 12 of 12 template and all targeted cores. That man needs systemic therapy, likely ADT/ARPI doublet. The local disease is frankly the least of the concern. Su...