Do you use an SIB schema for salvage post-prostatectomy RT when treating the fossa in ~33-39 fractions and including the pelvic lymph nodes?
What is your preferred dose/fractionation schema for salvage post-RP RT when treating the fossa with conventional fractionation and including pelvic lymph nodes?
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Some have adopted 25 fraction regimens with the simultaneous delivery of 62.5 Gy to the operative bed and 45-50 Gy to the regional pelvic lymphatics, in part based on the randomized NRG-GU003 (Buyyounouski et al., PMID 38483412), which should be reporting updated results on efficacy and toxicity later this year. Others, owing to concerns for increased toxicity with hypofractionation (potentially confounded by simultaneous biological dose escalation), continue to utilize conventional fractionation (see discussed recently in question 24308 on this forum). Data from RADICALS-RT seems to suggest comparable toxicity for a 20 fraction regimen to conventional fractionation, although this was a post hoc comparison, which may merit further scrutiny (Petersen et al., PMID 37150260). A second single-institution trial being run at MD Anderson, PORT-HYFX (NCT03987386; PI Dr. Quynh Nguyen), with the primary endpoint of toxicity, has completed and will add helpful information to the literature regarding the potential for increased rates of toxicity with hypofractionation.
Personally, off trial, I continue to utilize a two-phase approach with the first phase to 45-50 Gy followed by a sequential boost to the operative bed to a total dose of ≈64.8-66.6 Gy in conventional fractionation.
Agree with Dr. @Dr. First Last and the additional discussions about hypofrac that have been addressed elsewhere on MedNet.
I also favor a sequential approach when doing conventional fractionation (32-40 fractions).
To probe what a full SIB approach might look like, you're pushing potentially 150 cGy/Fx if doing 32 fractions to approach an 'EQD2' of 45 Gy in 25 Fx (EQD2 43.2 Gy). If you want to get there in 39 fractions, that's closer to 130 cGy/Fx (50.7 Gy). Off trial that's out of my comfort zone. For reference, with Dr. Nancy Lee's 30 Gy approach to H&N cancers, they always do cone down to 70 Gy instead of some SIB schema. While elective nodal vs fossa dosing isn't as extreme, I think it's a similar framework.
In contrast, I often will do SIB as part of the sequence. When I use sequential for say gross fossa and nodal disease I will do 25 fractions with 180 cGy/Fx to elective nodes and fossa, 200 cGy/Fx to gross fossa, and 225 cGy/Fx to gross nodes (higher depending on anatomy) then cone down for 12 fractions with 180 cGy/Fx to elective fossa and 200 cGy to gross fossa — cumulative 74 Gy in 37 to gross fossa disease, 66.6 Gy in 37 to entire fossa, 56.25 Gy (or more) in 25 Fx to gross nodes, and 45 Gy in 25 Fx to elective nodes.