Dosimetry Based PRRT Versus Standard Dose PRRT With Lu-177-DOTATOC in NEN Patients

In this study, we want to randomize patients with neuroendocrine neoplasms (NENs) who are eligible for peptide receptor radionuclide therapy (PRRT), to either standard PRRT consisting of 4 treatments with 7.4 GBq Lu-177-DOTATOC (standard arm) or 4 treatments with individualized doses of Lu-177-DOTATOC (dosimetry arm). In the dosimetry arm, the first dose depends on the patients' kidney function and thereafter the absorbed dose to the kidneys at the previous treatment. A max of 20GBq will be administered at the first treatment and 25GBq at treatment 2-4. We aim to reach an accumulated kidney dose of 24Gy.

After the first treatment all patients will go through three SPECT/CT scans 24 hours, 4 days, and 7 days, after treatment to calculate absorbed kidney dose. The patients in the standard dose treatment arm will have one SPECT/CT scan after each of the last three treatments; all performed 24 hours after treatment, used to approximate the kidney dose assuming the clearance of the Lu-177 DOTATOC is the same after all treatments. The patients in the dosimetry based treatment arm will go through three SPECT/CT scans after all four treatments for dosimetry calculation.

Bone marrow dosimetry is calculated after all treatments in the dosimetry based treatment arm and after the first treatment in the standard treatment arm. For bone marrow dosimetry, blood samples are drawn right before administration of Lu-177 DOTATOC (time 0) and 3 minutes, 45 minutes, 2 hours, 4 hours, 7-8 hours, 24 hours, 4 days, and 7 days after administration of Lu-177 DOTATOC.

Standard blood samples are routinely drawn every 2nd week after every treatment in all included patients and analysed regarding liver, kidney and bone marrow function. Kidney clearance is evaluated with Tc-DTPA clearance at baseline.

Blood and urinary samples will be collected at baseline and 3 months after the last treatment for kidney fibrosis analyses.

At baseline, blood and urine samples are collected for a biobank. All included patients fill in validated quality of life questionaires at all treatments.

To evaluate the effect of the treatment, all patients will be evaluated with standard CT scans prior to treatment and 3 and 9 months after the 4th treatment. Ga-68 DOTATOC PET will be performed at baseline and 6 and 12 months after the last treatment.