Inguinal lymph nodes in patients undergoing clinical C-11 Acetate PET/CT for prostate cancer

Objectives C11-Acetate PET/CT imaging is increasingly utilized in evaluation of prostate cancer. Normal physiologic distributions has been reported in salivary glands, liver, spleen, pancreas, gastrointestinal tract, and kidneys, with minimal activity in the urinary bladder. We routinely visualize acetate accumulation in non-pathological inguinal nodes. We retrospectively analyzed studies performed at our institution from 1/08-12/09.

Methods 26 patients underwent PET/CT imaging with 18F-FDG and C11-Acetate for prostate cancer re-staging and staging purposes from 1/08-12/09. Out of 26 patients, 17 studies were without clinical and/or radiological evidence of nodal tumor involvement. One study was excluded due to technical reason (dose infiltration). Any patients with suspicion of nodal tumor involvement on dual radiotracer imaging were excluded. A 3cm ROI was drawn on bilateral inguinal regions with highest level of C11-Acetate uptake. SUVmax corrected for lean body mass were recorded.

Results Inguinal lymph nodes with varying intensities of C-11 acetate were visualized in each of the 17 patients without evidence of cancer in deeper nodes. Average SUVmax (lean body mass) in these typically bilateral inguinal lymph nodes was 1.5+/-0.7, with no significant difference in average SUVmax -lbm between right 1.6, and left 1.5. SUVmax range in right inguinal lymph nodes was 0.9-2.1 and 0.7-3.1 on the left. On 18F-FDG PET images, there was no evidence of abnormal FDG accumulation. On accompanying non diagnostic CT images, the inguinal lymph nodes were non-pathological according to CT criteria, i.e. fatty hilum and measuring up to 1cm. Physiological radiotracer distribution of C-11 acetate was noted in liver, pancreas, spleen and small bowel.

Conclusions C-11 acetate offers promise in detection prostate cancer, however it is normal to have some level of tracer uptake in clinically and radiologically normal inguinal lymph nodes which are not expected sites of involvement with prostate cancer