Multidisciplinary team interpretation performance for indeterminate bone uptake on PSMA PET during prostate cancer...

To compare the performance of a multidisciplinary team (MDT) with the proposed standardized PROMISE classification system for indeterminate bone uptake on staging PSMA PET.

744 staging PSMA PET/CT scans (140 ¹⁸F-PSMA-1007 and 604 ⁶⁸Ga-PSMA-11 PET/CT) were retrospectively reviewed for the presence of indeterminate bone metastatic staging. 95 scans which were discussed at an MDT meeting were further analysed for the comparison with the PROMISE classification system. MDT interpretation of the bone staging was recorded as positive or negative, based on risk stratification, imaging review, and clinically suitable management options. Additional resources were occasionally used, such as bone biopsy, musculoskeletal MRI, or re-evaluation after initial androgen deprivation therapy. MDT and PROMISE classification were compared for agreement. Statistical assessment was made on any differences in age, PSA, T-stage, Gleason score, risk, SUVmax and tracer used between negative and positive patients in both methods. Discordant cases were correlated with follow up data.

The overall incidence of indeterminate bone uptake in staging PSMA PET scans was 16.9%, reaching 40% for ¹⁸F-PSMA-1007. There was substantial agreement between MDT and PROMISE interpretation (87.3%). The MDT was more likely to interpret an indeterminate bone uptake as negative in patients with lower Gleason score and in scans where ¹⁸F-PSMA-1007 was used. The data from long-term follow up favoured the MDT interpretation in all the cases of disagreement. Examples of pitfalls in rib or thoracic spine foci of uptake are presented and recommendations for PET reporters and MDTs have been generated based on the results.

PROMISE may interpret indeterminate bone PSMA uptake with high accuracy. Therefore, PET reporters are recommended to use the PROMISE algorithm, while being mindful of common pitfalls related to the Gleason score, tracer used and anatomical localisation of indeterminate bone findings. Additional discussion in an MDT meeting is recommended with a view to resolve all equivocal findings.