ESTRO ACROP Delphi: salvage SBRT for intraprostatic relapse
TL;DRConsensus on only 14/40 items (35%) after 3 Delphi rounds; dose, fractionation, biopsy need and cumulative OAR constraints remain unresolved.
NRG/RTOG 0526MASTERPICTUREPROLAPSE
The dosimetric section, at Kendall's W 0.12, is where the panel agreed least: no consensus on salvage dose relative to primary, fractionation, or cumulative rectum/bladder limits. What it does fix is the target and sequencing: focal CTV of mpMRI GTV plus an adaptive margin, no concurrent ADT, and a 2-year minimum interval from primary RT.
In an M0, ECOG 0-1 man with intraprostatic relapse ≥2 years after primary RT, this expert opinion supports focal SBRT without concurrent ADT as a reasonable option; it does not tell you the dose, fractionation, cumulative OAR limits, or whether imaging alone can stand in for biopsy.
The dosimetric section, at Kendall's W 0.12, is where the panel agreed least: no consensus on salvage dose relative to primary, fractionation, or cumulative rectum/bladder limits. What it does fix is the target and sequencing: focal CTV of mpMRI GTV plus an adaptive margin, no concurrent ADT, and a 2-year minimum interval from primary RT.
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ESTRO ACROP Delphi consensus, 40-item questionnaire in 3 rounds (Jul 22 to Dec 16, 2019). Items with >80% agreement were retired as consensus; an EAU-nominated urologist sat on the reviewing committee.
Panel of 18 of 33 invited authors of salvage SBRT papers (54.5%), all completing every round. 12/18 work in centres treating >2,000 pts/yr; only 2 practise outside Europe.
Consensus on a focal CTV (mpMRI GTV + adaptive margin), dose prescribed to the isodose, and no concomitant ADT. Schedules in use were 5-6 fx up to about 35 Gy, but the panel did not agree on a recommended fractionation or on dose relative to the primary course.
14/40 items reached consensus (35%), half of them in round 1; consensus or major agreement on 27/40 (68%). Agreement was highest for imaging/staging (W 0.34) and lowest for dosimetry (W 0.12).
| Section | Consensus items | Kendall's W | Agreement |
|---|---|---|---|
| Patient selection | 6/19 | 0.17 | Weak |
| Imaging + biopsy | 3/7 | 0.34 | Moderate |
| Dosimetry (CTV + OARs) | 5/14 | 0.12 | Very weak |
The Uro-GEC-ESTRO salvage brachytherapy Delphi split on whole-gland vs focal targets and mandated histology; this panel agreed on focal GTV-based CTV but split on biopsy. The Italian AIRO PROLAPSE survey leaned toward concurrent ADT, which this panel rejected.
Rounds closed before most PSMA-PET data appeared, so the 28% PSMA-PET endorsement is dated. Panellists were selected as authors of the mostly retrospective, short-follow-up series the consensus draws on, which risks circular endorsement.
The unresolved items (biopsy, dose, cumulative OAR constraints) are the ones a prospective protocol has to fix first. The ongoing trials cited already disagree with each other on interval (2 vs 4 yr) and on whole-gland vs partial CTV.
- Optimal salvage SBRT dose and fractionation relative to the primary course
- Can PSMA-PET/mpMRI replace biopsy before prostate re-irradiation? recruiting Stereotactic Re-irradiation of Local Recurrences of Prostate Cancer After Radiotherapy Phase 2n=55 · primary completion 2029-12 · phase 2 SBRT reRT; biopsy or MRI+PSMA-PET eligible
- Cumulative OAR constraints for prostate re-irradiation
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The longer read
The value of this document lies less in what the panel agreed on than in where it could not agree. Most of the consensus items describe things a careful radiation oncologist would already do before re-irradiating a prostate: exclude metastatic disease, restrict to ECOG 0-1, do not treat early relapses, and use the Phoenix definition in follow-up. The section that matters most for planning, dose and organs at risk, produced the weakest concordance of the three, with a Kendall's W of 0.12. The panel could not say whether the salvage dose should be higher, lower or equal to the primary course, could not settle on a fractionation, and could not agree on a cumulative constraint for rectum, bladder, femoral heads or penile bulb. Anyone starting a salvage SBRT program will therefore still be choosing those parameters from single-institution experience.
Two positions do carry practical weight. The first is the focal target: CTV defined as the mpMRI GTV plus an adaptive margin. That departs from the Uro-GEC-ESTRO brachytherapy Delphi, which split on whole-gland versus partial targets, and it sits alongside the Corkum systematic review the authors cite, which found no gain in local control or bRFS from whole-prostate re-irradiation and less severe late toxicity with partial re-treatment. The second is the rejection of concurrent ADT, framed explicitly as a way to delay ADT and its quality-of-life cost. The Italian PROLAPSE survey leaned the other way, which shows how far practice varies even within one national community.
Methodology should temper confidence in several ways. The panel was drawn from authors of the salvage SBRT literature, which the discussion itself describes as retrospective with short follow-up; experts endorsing the approach they publish on is a structural bias of this design. The questionnaire was adapted from a brachytherapy instrument and, by the authors' account, built mainly from clinical experience because the data were thin. Timing matters too: the low PSMA-PET endorsement (28% vs 89% for choline PET) reflects rounds that closed before most PSMA-PET detection data were published, so a reader should not take it as a current imaging position.
The biopsy split is the most consequential open question. Guidelines and the MASTER meta-analysis keep histology as the filter against radiological false positives, while only 22% of this panel called biopsy always necessary. The PICTURE data cited (mpMRI avoiding repeat biopsy in 14% with 97% detection of clinically significant disease) were not generated in the post-RT setting, so they support the question rather than answer it. The consensus is a reasonable scaffold for trial eligibility; it is not evidence that salvage SBRT controls disease, which still rests on the retrospective series and the ongoing prospective protocols.