This study presents the biodistribution, safety and absorbed dose of 123I-VIP administered to 18 patients with intestinal adenocarcinomas or endocrine tumors.
Methods: To achieve high-specific activity, 123I-VIP was purified by HPLC. Following intravenous administration of 123I-VIP (172 +/- 17 MBq (4.65 +/- 0.5 mCi); < 300 pmole ( < 1 microgram)/patient), sequential images were recorded during the initial 30 min. Thereafter, whole-body images were acquired in anterior and posterior views at various time points. Dosimetry calculations were performed on the basis of gamma camera data, urine, feces and blood activities.
Results: After injection of labeled peptide, the lung was the primary site of 123I-VIP uptake. Peak lung activity represented 40% +/- 7% of the injected dose at 0.7 hr and declined to 21% +/- 7% at 3.5, to 14% +/- 3% at 7 and to 8% +/- 4% 22 hr postinjection. Radioactivity was excreted into the urine and amounted to 37% +/- 16% of the injected dose within 4, 68% +/- 12% within 8, 82% +/- 16% within 16 and 93% +/- 8% within 24 hr postinjection. The mean effective half-life of 123I-VIP in the lungs was 2.2 and 6 hr in the urinary bladder. The highest radiation absorbed doses were calculated for the lungs [67 muGy/MBq (248 mrad/mCi)], urinary bladder [77 muGy/MBq (284 mrad/mCi)] and thyroid gland [104 muGy/MBq (386 mrad/mCi)]. The effective dose was 28 muSv/MBq (104 mrem/mCi).
Conclusion: HPLC-purified 123I-VIP shows favorable dosimetry and is a safe and promising peptide tracer for localization of tumors expressing receptors for VIP.