Page 42 - Towards personalized therapy for metastatic prostate cancer: technical validation of [18F]fluoromethylcholine

Chapter 2
with PSA relapse. However, their dual-phase PET/CT protocol included WB scans with variable early and late acquisitions, 5 to 15 min p.i. and 65 to 200 min p.i., respectively. The discrepancy may be explained by the rapid clearance of the [18F]FCH after administration [14, 16], which implies that timing of the early acquisitions is crucial and should be done using a strict imaging protocol.
The prevalence of patients with inguinal lymph nodes showing enhanced [18F]FCH uptake was 12% (8/66 patients). Our finding that reactive nodes remained detectable over time (i.e., for 30 min after injection) seems being inconsistent with the observation of Price et al. [16] who found persistent uptake at the late, 45 min p.i., images in only 1 of 4 patients with initially enhanced inguinal node uptake. We content that this variance results from improved signal to noise ratios with the current TF scanner generations.
Our data suggest that the type B pattern is a strong indication for malignancy, the PPV being 97% (35/36; see Table 3, for the best LN status predictor: SUVmax Relative Difference). The fact that the PPV is not 100% implies in clinical practice that, e.g. in case of multiple potentially malignant [18F]FCH positive LN, the ones with type B patterns should be the primary biopsy candidates.
Our results also suggest that a single point measurement in the context of a whole body scan, starting in caudocranial direction, 30 min after injection, is a reasonable alternative for relative change to differentiate reactive from malignant LN in patients with PC. Obviously, omitting the early scan would simplify the scan procedure. However, compared to measuring relative changes, the use of absolute SUV’s is more demanding at the level of standardization. Evidently, the present results pertain to lymph nodes with enhanced [18F]FCH uptake and ≥ 8 mm short axis. Ascertaining the single time-point approach requires validation versus histopathology.
CONCLUSION
Time-trends of enhanced [18F]FCH uptake in lymph nodes of prostate cancer patients seem to help discriminate benign from malignant localizations. Single time-point SUV measurements, 30 min p.i., may be a reasonable alternative for predicting the nodal status, but this remains to be validated in non-enlarged pelvic lymph nodes.
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