Ra-223 SPECT for semi-quantitative analysis in comparison with Tc-99m HMDP SPECT: phantom study and initial clinical experience

• Published in: EJNMMI research Vol. 7; no. 1; p. 81
• Main Authors: Owaki, Yoshiki, Nakahara, Tadaki, Kosaka, Takeo, Fukada, Junichi, Kumabe, Atsuhiro, Ichimura, Akira, Murakami, Mikoto, Nakajima, Kiyotaka, Fukushi, Masahiro, Inoue, Kazumasa, Oya, Mototsugu, Jinzaki, Masahiro
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 03.10.2017; Springer Nature B.V; SpringerOpen
• Subjects: Bone metastasis; Cardiac Imaging; Collimation; Collimators; Correlation analysis; Feasibility studies; Image contrast; Image quality; Imaging; Lesions; Medicine; Medicine & Public Health; Nuclear Medicine; Oncology; Original Research; Orthopedics; Patients; Photopeak; Prostate; Prostate cancer; Quantitation; Quantitative analysis; Ra-223; Radiology; SPECT; Spheres; Tc-99m; Tc-99m; Bone metastasis; Quantitation; Ra-223; SPECT
• ISSN: 2191-219X; 2191-219X
• DOI: 10.1186/s13550-017-0330-z

Background Image-based measurement of absorbed dose of Ra-223 dichloride may be useful in predicting therapeutic outcome in patients with castration-resistant prostate cancer (CRPC). In general, SPECT has been found to be more accurate than planar imaging in terms of lesion-based analysis. The aims of this study were to assess the feasibility and clinical usefulness of Ra-223 SPECT. The energy spectrum of Ra-223 and SPECT images of a cylindrical phantom with a hot rod were obtained to determine the collimator candidates and energy window settings suitable for clinical Ra-223 SPECT (basic study A). Another phantom with a tube-shaped chamber and two spheres simulating bowel activity and metastatic lesions in the lumbar spine was scanned with medium-energy general-purpose (MEGP) and high-energy general-purpose (HEGP) collimators (basic study B). Ten patients with CRPC underwent SPECT imaging 2 h after Ra-223 injection successively with MEGP and HEGP collimators in random order for 30 min each. Lesion detectability and semi-quantitative analyses of bone metastasis (i.e. lesion-to-background ratio (LBR)) were performed compared to Tc-99m HMDP SPECT. Results Basic study A revealed that an 84-keV photopeak ± 20% using the HEGP collimator offers better SPECT image quality than the other imaging conditions. Basic study B showed that uptake in one of the spheres was overestimated by overlapped activity of the tube-shaped chamber in planar imaging whereas the spheres had similar counts and significantly higher sphere-to-background ratio in SPECT. On both planar and SPECT images, HEGP gave higher image contrast than MEGP ( p  < 0.01). In the clinical study, Ra-223 SPECT at 84 keV ± 20% depicted more lesions with the HEGP than with the MEGP collimator (51 vs 36, p  = 0.013). There was a positive correlation between LBR in Tc-99m SPECT and in Ra-223 SPECT ( r  = 0.67 with the MEGP and 0.69 with the HEGP collimator, p  < 0.01). LBRs were significantly higher with the HEGP than with the MEGP collimator ( p  < 0.01). Conclusions We recommended the use of the HEGP collimator at 84 keV ± 20% for Ra-223 SPECT imaging. Lesion-based semi-quantitative analysis in the human study revealed a good correlation between Ra-223 and Tc-99m HMDP SPECT in the early phase (2–3 h post injection).