Abstract
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Objectives Osseous metastases (OM) and therapeutic response are monitored by visual evaluation of bone scintigraphies (BS). The aim of this SPECT/CT study was to compare visual evaluation of changes in tracer uptake with quantitation of tracer uptake in absolute units.
Methods Data from 19 patients was analyzed retrospectively. Each patient underwent two BS with SPECT/CT four h p.i. with ca. 8 MBq/kg of Tc-99m-DPD. An average of 10.3 months elapsed between time points one and two (TP 1/2). Using a previously published protocol [1], the SPECT/CT camera was calibrated to allow quantification in absolute units. In both planar scintigrams and SPECT/CT, two independent readers visually compared tracer uptake in up to six OMs per patient (total 52) at both TPs and classified as regressive, stable or progressive. Subsequently, quantitative analysis was performed measuring peak standard uptake values (SUV) and also classified as regressive (>25% decrease), progressive (>25% increase), or stable (rest). If available, uptake in reference regions in the lower thoracic or lumbar spine was also determined.
Results In OMs at TP1 and TP2, SUV peak (± SD) was found to be 20.3 (± 26.4) and 13.3 (± 9.5), respectively. For the reference regions, SUV mean was 5.6 (± 1.5) and 4.7 (± 2.0) and showed no significant change due to a treatment with bisphosphonates. Agreement between quantitative and visual assessment was only moderate with a κ value of 0.34 for planar scintigraphy and of 0.47 for SPECT/CT. Discrepancies in visual and quantitative assessment occurred in 17 of 52 lesions (32.7%).
Conclusions Compared to measuring DPD uptake in absolute units, visual evaluation of skeletal scintigraphies for tumor response to therapy is considerably more inaccurate, yielding inconsistent results in up to 33% of the cases.