This is from a recent ASCO review of biochemically recurrent PCa management. Their long story/short story conclusion is to include ADT to SRT only at a PSA above 0.5.
Here's the long story excerpt from their paper, which references the OP's paper:
https://ascopubs.org/doi/full/10.1200/edbk_200319"Addition of androgen-deprivation therapy to salvage radiotherapy."
Recently, two randomized phase III trials of salvage RT with or without androgen pathway inhibition have reported their results.37,38 These trials have generated numerous questions given their discordant results, which are likely rooted in the differences in the cohorts themselves, treatment arms, and follow-up duration. RTOG 9601 tested the addition of 2 years of bicalutamide monotherapy to salvage RT.37 The trial had a median follow-up period of 13 years, and the patients enrolled were high risk by modern standards (67% had T3 disease, 75% had positive margins, 12% had persistently elevated PSAs > 0.5 ng/mL after prostatectomy). Furthermore, RT was delivered primarily as late salvage RT, in that only 10% of men had salvage RT when PSA was 0.2 to 0.3 ng/mL, 25% had PSA levels greater than 1.0 ng/mL, and the median PSA level was 0.6 ng/mL. Bicalutamide was associated with a reduction in distant metastasis and improvement in overall survival. However, the benefit on subset analysis was limited to men who underwent late salvage RT with PSA levels greater than 0.7 ng/mL.
The GETUG-AFU-16 trial tested the addition of 6 months of a luteinizing hormone–releasing hormone agonist to salvage RT.38 This study had a median follow-up period of 5.3 years, and patients were more analogous to contemporary treated patients (46% had T3 disease, 51% had positive margins, and the trial did not permit persistently elevated PSA levels after prostatectomy). Overall the cohort was lower risk then men enrolled in RTOG 9601. Furthermore, 75% of patients on the trial underwent early salvage RT, and only 10% of patients underwent salvage RT at PSA levels greater than 1.0 ng/mL. In this more favorable-risk population undergoing early salvage RT, the investigators did not find a significant difference between arms with regard to distant metastasis or overall survival. They did report an improvement in biochemical control from the addition of ADT, which would be expected to be improved in patients receiving PSA-lowering therapy and is of unclear clinical significance. However, similar to RTOG 9601, they did demonstrate that men with PSA levels greater than 0.5 ng/mL appeared to derive the greatest benefit from the addition of ADT. Similar findings have been recently reported from retrospective studies demonstrating that only men with a high risk for recurrence appear to derive a benefit from the addition of ADT to salvage RT.39
So what can one conclude from these two very different trials? Despite the numerous differences between RTOG 9601 and GETUG-AFU-16, it is clear that men undergoing late salvage RT (PSA > 0.7 ng/mL) with high-risk features (Gleason score 8–10, T3 disease, and/or positive margins) appear to derive a metastasis and survival benefit from the addition of long-term hormonal therapy on the basis of RTOG 9601.37 Furthermore, men who undergo early salvage RT have yet to demonstrate clinically meaningful benefits with regard to reductions in metastasis or death from prostate cancer from the addition of androgen pathway inhibition. A recent framework from a panel of multidisciplinary experts based on the available evidence can be used to help personalize the use of ADT for men receiving salvage RT and recommends omission of ADT for men undergoing early salvage RT.40 The culmination of the data has inspired a recently approved phase II randomized NRG Oncology cooperative group trial, NRG GU-006, to investigate if men undergoing primarily early salvage RT will benefit from enhanced antiandrogen therapy (apalutamide, a second-generation antiandrogen) versus placebo.