Page 39 - Towards personalized therapy for metastatic prostate cancer: technical validation of [18F]fluoromethylcholine

Dual-phase [18F]FCH PET/CT in prostate cancer
Of the inguinal nodes (14 type A and 1 type B with stable uptake over time) none showed
signs of malignancy during follow-up; of these, in one patient a lymph node biopsy
was tumor negative. One patient (2 LN) opted for watchful waiting policy (otherwise
negative PET), and his PSA was stable at 0.4 ng/ml for the follow-up of 12 months. In
another patient (type A LN) a local recurrence was treated with HIFU with good clinical
response (PSA) and no signs of progression. 2
DISCUSSION
In our referral-based spectrum of patients with enhanced [18F]FCH uptake in pelvic and inguinal lymph nodes, decreasing [18F]FCH uptake over time seems to be a reliable tool to differentiate benign and malignant nodes. Together with similar findings by others to classify radioactive choline positive lesions suspected to represent hematogeneous metastases, our results are relevant for clinical decision making and simplification of diagnostic procedures, e.g., in patients with elevated PSA and positive [18F]FCH PET findings. Moreover, the results underline the relevance of a sequential PET imaging protocol after a single injection of [18F]FCH to account for the time-trend of tracer uptake.
We classified disease-status as malignant for enlarged pelvic nodes, and as benign for inguinal nodes of any size. Our criterion of benignity was based on the typical prostate drainage pattern which does not include inguinal nodes, as described by Inoue et al. [20]. They identified by using fluorescence navigation 3 lymphatic drainage pathways, comprising the obturator, the external and internal iliac nodes. Similar drainage patterns were found by Tokuda et al. [21] in 125 patients with LN metastases. Weckermann et al. [22] performed both sentinel lymph node dissection and radical prostatectomy in 1055 patients with PC. Despite a high percentage (> 50%) of positive nodes identified outside the standard lymphadenectomy borders, none of them were found in the inguinal region. In our study we also never encountered occurrences of malignancy in inguinal nodes (histological analysis, clinical radiological follow-up).
We considered pelvic nodes with a short axis diameter equal or exceeding 8 mm as being malignant. This threshold was chosen based on the study of Jager et al. [23] who reported a 98% specificity for MRI using this dimension. In their meta-analysis, Hövels et al. [31] found that false positivity of CT / MRI (similar performance for either
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