Aim/Introduction: The use of the Ac-225 in radionuclide therapy has recently become popular. Therapeutic use should involve an attempt
to estimate the absorbed dose, which in the case of Ac-225 is not an obvious task. It is related to the decay chain involving many isotopes
with different physicochemical properties. However, the first step to calculate the absorbed dose is proper quantitative imaging. The study
aimed to confirm the feasibility of SPECT/CT imaging of Ac-225. In particular, to present qualitative and qualitative assessment of the
received images. Additionally, to present the SPECT image quantitative calibration method, as well as validation measurements and their
accuracy. Materials and Methods: A collarless Jaszczak phantom with cylindrical sources of various sizes was filled with Ac-225 solution.
The initial activity concentration was 235 kBq/ml. SPECT/CT imaging was performed after filling the phantom, using a Siemens Symbia T6
with HE collimators. Three energy windows were considered: I. 440 keV (width 10%, Bi-211), II. 218 keV (width 10%, Fr-221), III. 78 keV (width
20%, Ac-225 with bremsstrahlung X-rays).Five combinations were used: only I, only II, only III, sum I+II, sum I+II+III. DEW or TEW method
was used for SC. AC based on CT images was performed. Other imaging parameters were as follows: 64 images per detector, time per image
of 30 s, OSEM Flash 3D using 8 subsets, 10 iterations, Gaussian filter (FWHM 4 mm). Additionally, the 3D printed model of the glioblastoma
tumour was developed and imaged to evaluate the accuracy of the chosen protocol.
Results: The contrast, signal-to-noise ratio and coefficient of variance in the images will be presented, as well as for quantification -
calibration factor CF and recovery coefficients RC. The maximum value of CF was calculated for setting I+II+III (21 cps/MBq). Using the
calibration factor and recovery coefficients obtained, the activity in a 3D-printed model of a glioblastoma tumour with uncertainty of no
more than 10% and satisfying accuracy for (I+II+III) energy window setting was quantified. Conclusion: Our results showed the possibility of
Ac-225 SPECT/CT imaging with good quality in all combinations of energy windows. Moreover, quantification of Ac-225 SPECT/CT image
could be performed with satisfactory accuracy and uncertainty for multiple energy window settings. There are still many challenges that
need to be considered in further research on alpha emitter imaging (including high noise in the image, and other than standard SC
scattering correction methods).
TULIK Monika;
KULINSKI Radoslaw;
TABOR Zbislaw;
BRZOZOWSKA Beata;
LABA P.;
BRUCHERTSEIFER Frank;
MORGENSTERN Alfred;
KROLICKI Leszek;
KUNIKOWSKA Jolanta;
2024-11-07
SPRINGER
JRC138959
1619-7089 (online),
https://link.springer.com/article/10.1007/s00259-024-06838-z,
https://publications.jrc.ec.europa.eu/repository/handle/JRC138959,
10.1007/s00259-024-06838-z (online),
