Despite an unconfirmed utility, dynamic 11C-Choline PET/CT (D-PET/CT) is clinically used by several PET centres to assess the presence of 11C-Choline uptake suggesting local relapse. In this setting the possible use of dynamic PET/CT in evaluation of pelvic lymph-nodes has not been investigated before. As described on the literature 11C-Choline PET/CT represent an useful diagnostic tool for planning radiotherapy (RT) of local or lymph-nodes relapse in patients with biochemical relapse after prostatectomy.
The aim of this retrospective study was to evaluate the possible use of D-PET/CT study to improve the assessment of patients with rising PSA after prostatectomy candidates to RT.
Thirty patients with rising PSA (average PSA: 2.69ng/ml; median PSA: 1.93 ng/ml; Range 0.94-6.5 ng/ml) after prostatectomy who underwent to RT on suspicious local or lymph-nodes disease revealed by 11C-Choline PET/CT, were identified retrospectively in our database. In addiction to standard PET/CT acquisition (from vertex to mid-thigh), a post-injection D-PET/CT study was performed focusing on the pelvic region in all patients before RT. Early 11C-Choline uptake in the dynamic phase at the level of primary local region, corresponding to a morphological finding on CT and avid in the standard PET/CT acquisition were considered as suggesting for local relapse. In a qualitative evaluation, presence of asymmetry and abnormal uptake at lymph-nodes stations were used to define lymph-nodes D-PET/CT positivity (positive/negative evaluation) comparing with final PET/CT findings. PSA levels after treatment and clinical outcome (as progression free survival-PFS; minimal follow-up of 12 months) were available to test the potential value of D-PET/CT in a standard clinical scenario.
D-PET/CT showed 11C-Choline uptake on the prostate bed, also confirmed by standard PET/CT acquisition in 7/30 patients. In 4/7 patients, possible local relapse was coupled with presence of 11C-Choline uptake on both standard and dynamic acquisition at the level of pelvic lymph-nodes. All these seven patients had RT at the site of suspicious local relapse and/or simultaneous integrated boost on the avid lymph-nodes following reduction of PSA after treatment (mean PSA: 0.14ng/ml; median PSA: 0,02ng/ml; Range 0-0.68ng/ml) and good control of disease characterised by long PFS (mean: 30,9 months; median: 30,5).
In the remaining 23 patients D-PET/CT demonstrated the presence of avid pelvic lymph-nodes in 15 cases that showed always final high avidity in the standard PET/CT examination. These patients were treated by RT using PET images in the planning treatment. In every patients sensible reduction of PSA levels at the first control and good clinical outcome after RT were obtained. Only 4 out of 15 patients had biochemical relapse after long time (PFS >24months).
In addiction, mimicking a clinical scenario, D-PET/CT was useful in the decision making to discriminate lymph-nodes uptake to urethral urine activity in 3/30 patients and to distinguish inflammatory lymph-nodes (negative at dynamic acquisition) in 6/30 patients. These 9/30 patients did not received any local treatment showing no progression of disease during the follow-up.
D-PET/CT could represent a valuable tool to evaluate presence of local relapse and lymph-nodes disease as an added value to the standard examination for patients candidates to local treatment.

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