Gnanasegaran, G.; (2004) Methods to assess the biodistribution of radiolabelled somatostatin analogues and treatment response of neuroendocrine tumours. Doctoral thesis , University of London.

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Abstract

Introduction: During the past decade, proof of the principle that somatostatin receptors can be successfully used for in vivo targeting of neuroendocrine tumours (NETs) has been provided. These tumours are imaged with 111Indium-pentetreotide and treated with 90Yttrium labeled somatostatin analogues. The aim of this study was to assess (a) the biodistribution and residency of 90Y labelled agents using the brehmsstrahlung imaging technique (b) the tumour response to various treatment modalities using a simplified scintigraphic method [Functional SPECT tumour volume (STV)]. Material and methods: 1) 19 patients with NETs were imaged with 111In-pentetreotide and 14 of them underwent treatment with 90Y-lanreotide. The rest underwent treatment with 90Y-SMT. All the patients were imaged 24 hours post-therapy. Brehmsstrahlung images obtained post therapies were used to assess the 90Y-lanreotide biodistribution in 14 patients and the 5 patients treated with 90Y-SMT, comparing them with 111In-pentetreotide. 2) In 42 patients with NETs a retrospective analysis was performed of the 111In-pentetreotide imaging and CT scan in patients treated with different therapies. A simplified scintigraphic method using 111In-pentetreotide SPECT liver imaging was used to monitor changes in tumour response and to determine how this correlates with CT scan and clinical response. Results: 1) 90Y-lanreotide and 90Y-SMT (with amino acids) have much lower uptake in the kidney (p 0.000 and 0.041 respectively) than 111In-pentetreotide. G Gnanasegaran MD 2 2) 22/42 patients had a good clinical response. A mean fall in total functional STV of 37% was seen in patients with symptomatic relief and a mean increase of 72 % was seen in patients with no symptomatic relief STV predicted the clinical outcome in 34 patients (81%) and CT predicted the outcome in 21 (50%) patients. Conclusion: There was a difference in biodistribution between 111In-pentetreotide and 90Y-lanreotide/ 90Y-SMT, especially in the kidneys, which may explain why there is minimal renal toxicity reported with 90Y-lanreotide/ 90Y-SMT therapies. Finally, the assessment of functional STV is more useful in monitoring the tumour response after treatment than CT. The changes in functional volumes after therapy correlate well with clinical response.

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