Repeatability of ⁶⁸Ga-PSMA-HBED-CC PET/CT–Derived Total Molecular Tumor Volume

Semiautomatic total tumor segmentations with red overlay designating sites of segmented lesions in scans 1 and 2 for patient with disease limited to prostate and left pelvic lymph nodes (A) and patient with extensive skeletal metastases (B). Interval between scans was 2 d for both patients.

Examples of segmentation challenges on ⁶⁸Ga-PSMA-HBED-CC PET/CT. Segmented tumor metastases are shown in red. (A) Metastasis in os ilium was segmented as single lesion on first scan but as 3 separate lesions in second scan (encircled). (B) Metastasis in rib was segmented accurately on first scan but inaccurately on second scan, with isocontour including portion of lung (encircled). Error was resolved manually.

Analysis of individual manually segmented ⁶⁸Ga-PSMA-HBED-CC–avid lesions. Linear regression and Bland–Altman plots (A and B) of MTV_lesion show correlation between scans. (C) Association is noted between MTV_lesion and SUV_max changes between scans 1 and 2.

Analysis of semiautomatic whole-body segmentation of ⁶⁸Ga-PSMA-HBED-CC–avid lesions. Linear regression (A and C) and Bland–Altman plots (B and D) of MTV_total and mean SUV_max show excellent correlation between scans and suggest no association between total tumor volume or lesion intensity and test–retest differences. Results for readers 1 and 2 were averaged for purposes of these graphs. (A and C) MTV_total and mean SUV_max for scan 1 are plotted separately against same metric for scan 2. (B and D) Mean of MTV_total or mean SUV_max between scans 1 and 2 was plotted against absolute difference in metric between 2 scans.

Graphical analysis of intra- and interreader agreement in reporting MTV_total, showing high correlation in measures between scans 1 and 2 for same reader (reader 1) (A) and showing high correlation in measures between 2 independent readers for same scan (scan 1) (B).