Target Volume Definition In High-Risk Prostate Cancer Patients Using Sentinel Node Spect/Ct And F-18-Choline Pet/Ct

Background: To assess the influence of sentinel lymph nodes (SNs) SPECT/CT and F-18-choline (F-18-FCH) PET/CT in radiotherapy (RT) treatment planning for prostate cancer patients with a high-risk for lymph node (LN) involvement.Methods: Twenty high-risk prostate cancer patients underwent a pelvic SPECT acquisition following a transrectal ultrasound guided injection of Tc-99m-Nanocoll into the prostate. In all patients but one an F-18-FCH PET/CT for RT treatment planning was performed. SPECT studies were coregistered with the respective abdominal CTs. Pelvic SNs localized on SPECT/CT and LN metastases detected by F-18-FCH PET/CT were compared to standard pelvic clinical target volumes (CTV).Results: A total of 104 pelvic SNs were identified on SPECT/CT (mean 5.2 SNs/patient; range 1-10). Twenty-seven SNs were located outside the standard pelvic CTV, 17 in the proximal common iliac and retroperitoneal regions above S1, 9 in the pararectal fat and 1 in the inguinal region. SPECT/CT succeeded to optimize the definition of the CTV and treatment plans in 6/20 patients due to the presence of pararectal SNs located outside the standard treatment volume. F-18-FCH PET/CT identified abnormal tracer uptake in the iliac LN region in 2/19 patients. These abnormal LNs were negative on SPECT/CT suggesting a potential blockade of lymphatic drainage by metastatic LNs with a high tumour burden.Conclusions: Multimodality imaging which combines SPECT/CT prostate lymphoscintigraphy and F-18-FCH PET/CT identified SNs outside standard pelvic CTVs or highly suspicious pelvic LNs in 40% of high-risk prostate cancer patients, highlighting the potential impact of this approach in RT treatment planning.