Analysis of quantitative [I-123] mIBG SPECT/CT in a phantom and in patients with neuroblastoma

Abstract

Purpose: To determine the accuracy of quantitative SPECT, intersystem and interpatient standardized uptake value (SUV) calculation consistency for a manufacturer-independent quantitative SPECT/CT reconstruction algorithm, and the range of SUVs of normal and neoplastic tissue.

Methods: A NEMA body phantom with 6 spheres (ranging 10-37 mm) was filled with a known activity-to-volume ratio and used to determine the contrast recovery coefficient (CRC) for each visible sphere, and the measured SUV accuracy of those spheres and background water solution. One hundred eleven 123I-metaiodobenzylguanidine ([I-123] mIBG) SPECT/CT examinations from 43 patients were reconstructed using SUV SPECT® (HERMES Medical Solutions Inc.); 42 examinations were acquired using a GE Infinia Hawkeye 4 SPECT/CT, and 69 were acquired on a Siemens Symbia Intevo SPECT/CT. Inter scanner SUV analysis of 9 regions of normal [I-123] mIBG tissue uptake was conducted. Intrapatient mean SUV variability was calculated by measuring normal liver uptake within patients scanned on both cameras. The intensity of uptake by neoplastic tissue in the images was quantified using maximum SUV and, if present, compared over time.

Results: The phantom results of the visible spheres and background resulted in accuracy calculations better than 5-10% with CRC correction. Interscanner SUV variability showed no statistical difference (average p value 0.559; range 0.066-1.0) among the 9 normal tissues analyzed. Intrapatient liver mean SUV varied ≤ 16% as calculated for 28 patients (87 examinations) studied on both scanners. In one patient, a thoracic tumor evaluated over 10 time points (18 months) underwent a 74% (3.1/12.0) reduction in maximum SUV with treatment.

Conclusion: The results demonstrate quantitative accuracy to better than 10%, and both consistent SUV calculation between 2 different SPECT/CT scanners for 9 tissues, and low intrapatient measurement variability for quantitative SPECT/CT analysis in a pediatric population with neuroblastoma. Quantitative SPECT/CT offers the opportunity for objective analysis of tumor response using [I-123] mIBG by normalizing the uptake to injected dose and patient weight, as is done for PET.

Keywords: Neuroblastoma; Nuclear medicine; Pediatrics; mIBG.

Fig. 1

Accuracy of quantitative SPECT. a NEMA body phantom imaged with a 3:1 ratio of [I-123] using the Symbia. b The SPECT contrast recovery coefficient (CRC) was calculated for the four visible spheres; for reference, PET CRC values are provided (GE Discovery 690 VCT)

Fig. 2

Interscanner SUV variability was plotted with outlier data (+) for 9 normal tissues imaged on an Infinia (left box plots-blue color) and on a Symbia (right box plots-black color). The SUVs values of the scanners were not significantly different

Fig. 3

Avid neoplastic tissue was quantified by SUV for images acquired on the Infinia and the Symbia combined

Fig. 4

Example of quantitative SPECT analysis of a patient undergoing treatment for 1 year and 4 months. a The primary paraspinal thoracic tumor was quantified by determining maximum SUV value and compared with long-axis length measurements of the larger presentation of the multifocal tumor. An SUV measurement was performed in the liver to provide a baseline SUV value for normal background uptake. b Transaxial reconstructed images were captured at 10 time points, with c selected coronal reformats shown to provide general context of the tumor size, avidity, and response to therapy compared to whole-body uptake

Fig. 5

Example of quantitative SPECT analysis of an 11 year old boy with relapsed neuroblastoma undergoing treatment. a Baseline occurrence—SUVmax = 3.8; b 35 days since baseline and after 2 courses of chemotherapy—SUVmax = 17.1; finally (c) 70 days since baseline—SUVmax = 23.9. d Tumor SUV was plotted compared to background liver SUV. Patient subsequently underwent radiotherapy