Interest of Late Images for the Assessment of Extensions in 18FGD PET-CT of Muscle-Invasive Bladder Cancers

The goal of this study is to demonstrate a significant gain in sensitivity versus surgical curage (extended pelvic) for initial lymph node staging of late FDG-PET images (2.5 hours) versus standard images (1 hour), analyzed by side (right iliac/left iliac areas in Patients with muscle-invasive bladder tumor (MIBT) (≥pT2) referred for FDG-PET in the nuclear medicine department of Hôpital Foch as part of their initial extension workup.

Before performing 18FDG PET-CT, the operator checks that the patient has fasted for at least 6 hours and that blood glucose levels are below 11 mmol/l. In the absence of contraindication, intravenous (IV) injection of the radiopharmaceutical (18FDG at a dose of 3 MBq/kg) and a diuretic (Furosemide 20mg) will be performed as part of routine care. The 18FDG PET-CT scan will be performed in 2 phases:

1st phase: Standard acquisition (vertex to mid-thigh) at 1 hour post-injection of radiotracer. PET acquisition is coupled to a "base-dose" CT scan in spontaneous contrast, for anatomical location, measurement of lymph node size, and creation of an attenuation map, necessary for correction of attenuation and diffusion on PET images (DLP estimated at around 500 mGy.cm on average). Micturition is performed as part of routine care just before the first acquisition.

Phase 2: Complementary abdomino-pelvic acquisition at 2.5 hours post-injection (2 or 3 steps depending on patient size. This second PET acquisition is coupled to an "ultra-base-dose" CT scan in spontaneous contrast, to be used only for attenuation and diffusion correction (DLP estimated at around 100 mGy.cm on average). Micturition is performed 30 minutes before the second acquisition.

The patient's proposed therapeutic management will be decided at the PCR once the extension work-up has been carried out, as part of routine care. For this purpose, only "standard" 18FDG PET-CT images may be used.

As a general rule, patients with distant metastases (stage pT2N+M+) will receive palliative treatment, while surgical treatment from the outset, or after chemotherapy for patients with stage pT2N0M0 or pT2N+M0, will be discussed on a case-by-case basis at the multidisciplinary consultation meeting.

Late" images will be used after lymph node curage, in patients who have not had chemotherapy prior to surgery (cystectomy + extended pelvic lymph node curage), to determine the sensitivity of these complementary images.