Evaluation of two intraoperative gamma detectors for assessment of 177Lu activity concentration in vivo

Abstract

BackgroundPatients with somatostatin receptor-expressing neuroendocrine tumours can be treated with intravenously administered 177Lu-octreotate. Few patients are cured with the present protocol due to the current dose limitation of normal organs at risk, such as the kidneys. By locally administering 177Lu-octreotate to the liver for the purpose of treating liver metastases, a substantially reduced absorbed dose to organs at risk could be achieved. The development of such a technique requires the capability of measuring the 177Lu activity concentration in tissues in vivo. The aim of this study was to evaluate different performance parameters of two commercially available intraoperative gamma detectors in order to investigate whether intraoperative gamma detector measurements could be used to determine 177Lu activity concentration in vivo.ResultsMeasurements were made using different sources containing 177Lu. Response linearity, sensitivity, spatial resolution and its depth dependence, organ thickness dependence of the measured count rate and tumour detectability were assessed for two intraoperative gamma detectors. The two detectors (a scintillation and a semiconductor detector) showed differences in technical performance. For example, the sensitivity was higher for the scintillation detector, while the spatial resolution was better for the semiconductor detector. Regarding organ thickness dependence and tumour detectability, similar results were obtained for both detectors, and even relatively small simulated tumours of low tumour-to-background activity concentration ratios could be detected.ConclusionsAcceptable results were obtained for both detectors, although the semiconductor detector proved more advantageous for our purpose. The measurements demonstrated factors that must be corrected for, such as organ thickness or dead-time effects. Altogether, intraoperative gamma detector measurements could be used to determine 177Lu activity concentration in vivo.

Feasibility of 177Lu activity quantification using a small portable CZT-based gamma-camera

“…Probe detectors for radio-guided surgery of neuroendocrine tumours have been used with [ 111 In]In-DTPA-Octreotide as tracer [ 7 ], and more recent investigations include [ 68 Ga]Ga-DOTA-TATE and [ 90 Y]Y-DOTA-TOC [ 8 , 9 ]. The application of portable intra-operative probes for 177 Lu detection and activity quantification has been addressed earlier [ 10 ]. Our group has previously investigated a hand-held gamma-camera system and successfully characterized its performance in 177 Lu measurement [ 11 ].…”