Feasibility of CT quantification of intratumoural 166Ho-microspheres

• Published in: European radiology experimental 2020-05, Vol.4 (1), p.1-11, Article 29
• Main Authors: C. Bakker, R., Bastiaannet, R., van Nimwegen, S. A., D. Barten-van Rijbroek, A., Van Es, R. J. J., Rosenberg, A. J. W. P., de Jong, H. W. A. M., Lam, M. G. E. H., Nijsen, J. F. W.
• Format: Article
• Language: English
• Subjects: Brachytherapy, Head and neck neoplasms; Diagnostic Radiology; Head & neck cancer; Humans; Imaging; Internal Medicine; Interventional Radiology; Medical imaging; Medicine; Medicine & Public Health; Neuroradiology; Original; Original Article; Radioisotopes, Tomography (x-ray computed); Radiology; Tomography; Ultrasound
• ISSN: 2509-9280; 2509-9280
• DOI: 10.1186/s41747-020-00157-2

Background Microspheres loaded with radioactive 166 Ho ( 166 Ho-MS) are novel particles for radioembolisation and intratumoural treatment. Because of the limited penetration of β radiation, quantitative imaging of microsphere distribution is crucial for optimal intratumoural treatment. Computed tomography (CT) may provide high-resolution and fast imaging of the distribution of these microspheres, with lower costs and widespread availability in comparison with current standard single-photon emission tomography (SPECT) and magnetic resonance imaging. This phantom study investigated the feasibility of CT quantification of 166 Ho-MS. Methods CT quantification was performed on a phantom with various concentrations of HoCl and Ho-MS to investigate the CT sensitivity and calibrate the CT recovery. 166 Ho-MS were injected into ex vivo tissues, in VX-2 cancer-bearing rabbits, and in patients with head-neck cancer, to demonstrate sensitivity and clinical visibility. The amount of Ho-MS was determined by CT scanning, using a density-based threshold method and compared with a validated 166 Ho SPECT quantification method. Results In the phantom, a near perfect linearity (least squares R 2 > 0.99) between HU values and concentration of 166 Ho was found. Ex vivo tissue experiments showed an excellent correlation ( r = 0.99, p < 0.01) between the dose calibrator, SPECT, and CT imaging. CT recovery was on average 86.4% ex vivo , 76.0% in rabbits, and 99.1% in humans. Conclusion This study showed that CT-based quantification of Ho microspheres is feasible and is a high-resolution alternative to SPECT-based determination of their local distribution.