These days, if there’s concern “… of the location of the tumor” such that “a gel spacer could not be used…”, the goto is BioProtect. (FDA-approved in 2023.)

As this paper states, “…if you're worried about microscopic extracapsular extension being displaced through the liquid of the spacer,…..the likelihood of spreading extracapsular cells is virtually nil.”
> https://www.urotoday.com/video-lectures/lugpa-2024/video/3006-symmetry-visibility-and-control-the-advantages-of-the-bioprotect-balloon-in-prostate-cancer-treatment-edward-soffen.html