SPARE Decision Console · v1.1 177Lu-PSMA · post-cycle 2 · mCRPC · research use only
SPAREalgorithm
SPECT-based · PET-sparing · management algorithm

Turn the cycle-2 SPECT into a management decision.

SPARE reads RECIP 1.0 on the 177Lu SPECT/CT already acquired for dosimetry, cross-checks the PSA trend, and reserves PET for the one cell where SPECT is genuinely uncertain. It returns an action.

Open the console See the algorithm
Continue RLT Perform FDG PET/CT Perform PSMA PET/CT Discontinue RLT
01 / CONSOLE

Response console

Set the cycle-2 findings — pick a category, or open ƒ to calculate it from measurements. The recommendation and its evidence update live.

Inputs

interim ≈ 12 weeks · after cycle 2
calculate RECIP from tumor volume
TTV baseline (mL)
TTV interim (mL)
ΔTTV — → —
RECIP 1.0: ≤ −30% → response · ≥ +20% or new lesions → progression.
calculate % change from PSA values
PSA baseline (ng/mL)
PSA interim (ng/mL)
ΔPSA — → —
≥ +25% → progression · ≤ −50% → response · otherwise stable.
Baseline PSA is most accurate on the day of cycle 1; interim ≈ 12 weeks.
calculate RECIP from tumor volume
TTV baseline (mL)
TTV on PET (mL)
ΔTTV — → —
Unlocks when SPECT is stable and PSA is stable.
02 / ALGORITHM

The decision tree

Your console inputs highlight the active path in real time. Tap any box to see the evidence and citations behind that decision.

Continue RLT Perform FDG PET/CT Perform PSMA PET/CT Discontinue RLT
  • Cycle-2 SPECT/CT
    RECIP 1.0
    • Response
      • PSA response / stableContinue RLT
      • PSA progressionFDG PET/CT
    • Stable disease
      • PSA responseContinue RLT
      • PSA stable
        • PSMA PET/CT
          RECIP 1.0
          • ResponseContinue RLT
          • StableFDG PET/CT
          • ProgressionDiscontinue RLT
      • PSA progressionDiscontinue RLT
    • Progressive diseaseDiscontinue RLT
evidence
Tap a decision

Select any box in the tree above — or change the console inputs — to see the rationale and citations behind that step.

Citations map to the numbered references below.

Evidence base

1Gafita A, Rauscher I, Weber M, Hadaschik B, Wang H, Armstrong WR, et al. Novel framework for treatment response evaluation using PSMA PET/CT in patients with metastatic castration-resistant prostate cancer (RECIP 1.0): an international multicenter study. J Nucl Med. 2022;63(11):1651–8.
2Kassas M, Jaafari A, Shagera QA, Devriendt L, Léger MA, Arçay Öztürk A, et al. SPECT versus PET for [177Lu]Lu-PSMA response assessment using quantitative RECIP 1.0. J Nucl Med. 2026;67(6):903–9.
3Unterrainer LM, De Leiris N, Unterrainer M, Delker A, Hempel L, Ells Z, et al. Evidence-based clinical protocols to monitor efficacy of [177Lu]Lu-PSMA radiopharmaceutical therapy in metastatic castration-resistant prostate cancer using real-world data. J Nucl Med. 2025;66(7):1054–60.
4Kassas M, Artigas C, Refalo N, Mallia A, Flamen P. Added value of interim FDG PET/CT in resolving PSA–PSMA discordance during PSMA-targeted radioligand therapy. Clin Nucl Med. 2026;51(2):191–3.
5Kassas M, Léger M-A, Poenaru R, Tahmi D, Zeiter RL, Shagera QA, et al. FDG PET/CT beyond mismatch exclusion in [177Lu]Lu-PSMA therapy: baseline prognosis and response assessment. The EANM Journal. 2026;4:100234.