An international quantitative SPECT/CT imaging exercise for Lu-177
Tran-Gia, J. Robinson, A. P. Calvert, Nicholas Denis-Bacelar, A. M. Fenwick, A. J. Ferreira, K. M. Finocchiaro, D. Fioroni, F. Grassi, E. Heetun, W.
Tran-Gia, J.
Robinson, A. P.
Calvert, Nicholas
Denis-Bacelar, A. M.
Fenwick, A. J.
Ferreira, K. M.
Finocchiaro, D.
Fioroni, F.
Grassi, E.
Heetun, W.
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Abstract
Aim/Introduction: Patient-specific dosimetry is required to
ensure the safety of molecular radiotherapy treatments
and to predict response. Dosimetry involves several steps,
the first of which is the determination of the activity of the
radiopharmaceutical taken up by an organ/lesion over time.
As uncertainties propagate along each of the subsequent
steps (integration of the time-activity curve, absorbed dose
calculation), establishing a reliable activity quantification is
essential. The MRTDosimetry project was a European initiative
to bring together expertise in metrology and nuclear medicine
research, with one main goal of standardising quantitative
Lu-177 SPECT/CT imaging based on a calibration protocol
developed and tested in a multicentre intercomparison.
Materials and Methods: The intercomparison included eight
SPECT/CT systems (3×Siemens, 4×GE, 1×Mediso). Each site
performed three measurements using the same acquisition
(medium energy collimator, 2×60 projections of 60s, 208keV
main energy windows) and reconstruction (OSEM with 25
iterations, 2 subsets, no postfiltering, attenuation correction
[CT-based], triple-energy-window scatter correction [6%-
20%-6% scatter-main-scatter], and resolution recovery [if
available]): 1. Determination of image calibration factor (ICF):
Counts (enlarged VOI around 216-mm Jaszczak cylinder filled
with ~400MBq) divided by activity and scan duration (unit:
cps/MBq). 2. Determination of recovery coefficients (RCs) for
partial-volume correction (PVC) in IEC NEMA body phantom
with 6 hot spheres (activity concentration ~2.0MBq/mL):
Activity in CT-based VOI (counts/ICF/scan_duration) divided
by each sphere’s activity. Recovery curve: Comparison
of weighted 3-parameter (b1/(1+(b2/volume)^b3)) and
2-parameter fit (b1:=1) of RCs against sphere volumes. 3.
Validation of quantitative imaging setup in 3D-printed
kidney and spleen phantoms filled with different activity
concentrations (kidney cortex & spleen: ~1.5 MBq/mL, kidney
medulla: ~0.5 MBq/mL) assembled in Jaszczak cylinder (custom-made baseplate for repeatable positioning): Activity
in CT-based VOI (counts/ICF/scan_duration) divided by
volume-dependent recovery value. An uncertainty analysis
was performed for all measurements. Results: Similar
combinations of imaging system and reconstruction led
to similar ICF values (Siemens 3/8”: [21.5±1.6] cps/MBq,
GE 3/8”: [45.4±2.5] cps/MBq). In the anthropomorphic
phantom validation, the mean ratios between SPECT-based
and radionuclide calibrator-based activity were very close
to the ideal value of 1 for the 3-parameter fit: 1.02±0.10
(kidney), 1.07±0.11 (spleen). Larger deviations were seen for
the 2-parameter-fit: 0.89±0.06 (kidney), 0.94±0.06 (spleen).
Conclusion: This comparison exercise shows that reliable
quantitative SPECT/CT is feasible when following the very
specific recommendations of the dedicated calibration
protocol developed within MRTDosimetry. In addition, for an
anthropomorphic phantom, the count loss due to spill-out
was successfully compensated by using a standardized PVC
based on sphere-based RCs.
Description
Date
2020
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Tran-Gia J, Robinson AP, Calvert N, Denis-Bacelar AM, Fenwick AJ, Ferreira KM, et al. An international quantitative SPECT/CT imaging exercise for Lu-177. European Journal of Nuclear Medicine and Molecular Imaging. 2020;47(SUPPL 1):S15-S6