Quantitative bone SPECT/CT-derived tumor burden as a prognostic biomarker in metastatic castration-resistant prostate cancer treated with Ra-223.

Authors

Yoshimitsu Fukushima, Go Kimura, Jun Akatsuka, Yoshimitsu Honda, Yujiro Nakaoka, Hiromitsu Hayashi, Shinichiro Kumita

Published in

EJNMMI reports. Volume 10. Issue 1. Jul 13, 2026. Epub Jul 13, 2026.

Abstract

Metastatic castration-resistant prostate cancer (mCRPC) is bone-predominant, requiring objective imaging biomarkers to guide Ra-223 therapy. We evaluated overall metabolic bone volume (OMBV) and overall total bone uptake (OTBU) from bone SPECT/CT as prognostic markers in mCRPC patients treated with Ra-223.
Thirty mCRPC patients underwent pre-treatment planar and SPECT/CT bone scintigraphy, with OMBV and OTBU derived using GI-BONE software. Overall survival (OS) was the primary endpoint; progression-free survival (PFS) and time to symptomatic skeletal event (TTSE) were secondary. Receiver operating characteristic analysis (Youden index) defined cut-offs for OS and TTSE independently. Treatment response was classified by composite changes in OMBV, OTBU, and bone scan index. OS, OMBV, and OTBU were analyzed by univariate Cox regression as continuous and dichotomized variables.
Baseline skeletal burden was substantial (median OMBV 1,191.21 cm³ [IQR 93.80-1,948.01]; median OTBU 9,746.18 [1,280.01- 17,587.11]); 87% had extent of disease grade 3-4. Post-treatment imaging in 24 patients yielded 10 responders (42%) and 14 non-responders (58%), with responder mean OMBV and OTBU reductions of 57% and 68%. Dichotomized baseline OMBV (hazard ratio [HR] 6.0320, 95% confidence interval [CI] 1.6880-21.5546; p < 0.001) and OTBU (HR 9.4492, 95% CI 2.0968-42.5826; p < 0.001) were significant predictors of OS. OMBV and OTBU were not significantly associated with PFS or TTSE.
OMBV and OTBU from bone SPECT/CT may provide useful prognostic information in mCRPC patients undergoing Ra-223 therapy, offering objective quantification of skeletal tumor burden using widely available technology. Further validation in larger cohorts is warranted.

PMID:
42437857
Bibliographic data and abstract were imported from PubMed on 13 Jul 2026.

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