A.V. Likhacheva1, L.A. Chipiga2, V.N. Vasileva3, D.A. Vazhenina4, V.Yu. Sukhov5, P.I. Krzhevitsk6, E.P. Daricheva7

1,2 Saint-Petersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev, Federal Service for Surveillance on Consumer Rights Protection and Human Well-Being (Saint-Petersburg, Russia)
1 The City Hospital No 40 of the Kurortny District (Saint-Petersburg, Russia)
2,4 A. Granov Russian Scientific Center of Radiology and Surgical Technologies of the Ministry of Health of the Russian Federation (Saint-Petersburg, Russia)
2 Almazov National Medical Research Centre of the Ministry of Health of the Russian Federation (Saint-Petersburg, Russia)
3 Peter the Great St. Petersburg Polytechnic University (Saint-Petersburg, Russia)
5 A.M. Nikiforov Russian Center of Emergency and Radiation Medicine (Saint Petersburg, Russia)
6 The N.N. Petrov National Medicine Research Center of oncology (Saint Petersburg, Russia)
7 LLC “GE HealthCare” (Moscos, Russia)
1 nastya.petryakova@gmail.com, 2 larisa.chipiga@gmail.com, 3 vvv1920@yandex.ru, 4 dariavazenina@mail.ru, 5 soukhov@mail.ru, 6 krzh@mail.ru, 7 elena.daricheva@gehealthcare.com

Radiopharmaceuticals labelled with alpha-emitting radionuclides, particularly 225Ac, are the most promising and interesting radiopharmaceuticals for the cancer treatment. Evaluation of the radiopharmaceutical distribution in the patient body using single photon emission computed tomography (SPECT) is one of the necessary steps during radiopharmaceutical therapy. The quantitative results of the accumulated activity of a radionuclide in an organ or lesion on SPECT images must be accurate and reproducible. To obtain accurate and reproducible results, SPECT quality control and calibration procedures should be performed including evaluation of the sensitivity and accuracy of the system reproducibility. The aim of the study is to evaluate the sensitivity of SPECT for 225Ac with different detection systems, data acquisition and image reconstruction parameters using three SPECT systems and the anthropomorphic phantom.

The sensitivity of SPECT for 225Ac was evaluate for three SPECT systems by different manufactures using Kyoto Kagaku PET/SPECT Thorax Phantom PH-63 which simulated patient body (torso with liver, kidneys, heart, lungs) with lesions in the region of the sternum and spine. The organs and lesions were filled with 225Ac solution. Phantom images were obtained with different collimators and different image reconstruction parameters with variable number of subsets and width of the Gaussian post-reconstruction filter. The sensitivity of SPECT was defined as ratio of measured counts (average and maximum values) on SPECT image in the region of interest (organ or lesion) and administered activity concentration in the region of interest multiplied by acquisition time.

The system with detectors based on cadmium-zinc-tellurium crystals and the system with scintillation detectors and a high-energy collimator had the best sensitivity. The high-energy collimator is the most appropriate for 225Ac imaging. The increase of the number of subsets leads to the increase of the sensitivity of SPECT for 225Ac; the increase of the width of the Gaussian filter leads to the decrease of the sensitivity of SPECT for 225Ac. Hence, the optimal reconstruction parameters for 225Ac SPECT imaging were determined as three-dimensional OSEM (ordered subset expectation maximization) reconstruction algorithm with 8 iterations and 32 subsets using a 4 mm Gaussian filter.

The sensitivity coefficients evaluated in the current work using anthropomorphic phantom can be applied as calibration coefficients to clinical images of patients with 225Ac obtained by the same SPECT systems.

Likhacheva A.V., Chipiga L.A., Vasileva V.N., Vazhenina D.A., Sukhov V.Yu., Krzhevitsk P.I., Daricheva E.P. Evaluation of the sensitivity of SPECT/CT systems for 225Ac. Biomedicine Radioengineering. 2025. V. 28. № 3. P. 5–14. DOI: https:// doi.org/10.18127/j15604136-202503-01 (In Russian)

1. Sgouros G., Bolch W.E., Chiti A. et al. ICRU REPORT 96, Dosimetry-Guided Radiopharmaceutical Therapy. Journal of the ICRU. 2021. V. 21. № 1. S. 1–212.
2. Bazhukova I.N., Bazhukov S.I., Baranova A.A. Tekhnologii yadernoj mediciny: Ucheb. posobie; M vo nauki i vyssh. obr. RF. Ekaterinburg: Izd-vo Ural. un-ta. 2022. 104 s. (In Russian)
3. Scheinberg D.A., McDevitt M.R. Actinium-225 in targeted alpha-particle therapeutic applications. Current Radiopharmaceuticals. 2011. V. 4. № 4. P. 306–320.
4. Morgenstern A., Apostolidis C., Kratochwil C., Sathekge M., Krolicki L., Bruchertseifer F. An Overview of Targeted Alpha Therapy with 225Actinium and 213Bismuth. Current Radiopharmaceuticals. 2018. V. 11. № 3. P. 200–208.
5. Majstrenko D.N., Stanzhevskij A.A., Vazhenina D.A., Odincova M.V., Popov S.A., Nomokonova V.B., Chipiga L.A., Saprykin K.A., Gromov A.V., Vasil'ev S.K. Radioligandnaya terapiya preparatami na osnove radionuklida 225As: opyt Rossijskogo nauchnogo centra radiologii i hirurgicheskih tekhnologij imeni akademika A. M. Granova. Luchevaya diagnostika i terapiya. 2022. T. 13. № 4. S. 86–94 (In Russian).
6. Kurtulus E., Benan K. Detailed chemistry studies of 225Actinium labeled radiopharmaceuticals. Current Radiopharmaceuticals. 2022.
   V. 15. № 1. P. 76–83.
7. Petrova A.E., Chipiga L.A., Vodovatov A.V., Stanzhevskij A.A., Majstrenko D.N., Lumpov A.A., Sinyuhin A.B., Bojkov I.V., Rameshvili T.E. Ocenka pogloshchennyh doz v organah pacientov ot vysvobozhdennogo radionuklida-metki pri provedenii radionuklidnoj terapii s 225As. Radiacionnaya gigiena. 2022. T. 15. № 1. S. 120–131 (In Russian).
8. Velichko E.N., Petrov A. N. Osnovy tomografii: Ucheb. posobie. SPb.: Izd-vo Politekhn. un-ta, 2017. 112 s. (In Russian)
9. Obespechenie i kontrol' kachestva issledovanij v radionuklidnoj diagnostike: Metodicheskie rekomendacii. M. SPb.: Izd-vo RHGA. 2023. 110 s. (In Russian)
10. International Commission on Radiological Protection. Nuclear Decay Data for Dosimetric Calculations. ICRP Publication 107. Ann. ICRP. 2008. V. 38. № 3.
11. Usmani S., Rasheed R., Al Kandari F., Marafi F., Naqvi S.A.R. 225Ac Prostate-Specific Membrane Antigen Posttherapy α Imaging: Comparing 2 and 3 Photopeaks. Clinical Nuclear Medicine. 2019. V. 44. № 5. P. 401–403.
12. Instruction Manual Thorax Phantom for RI. [Elektronnyj resurs]. URL: https://www.kyotokagaku.com/products_data/ph63_manual_ en.pdf (Data obrashcheniya: 29.07.2024).
13. Brudanin V.B., Gurov Yu.B., Rozov S.V., Sandukovskij V.G., Yakushev E.A. Harakteristiki detektorov na osnove kristallov kadmij-cink-tellur. Pribory i tekhnika eksperimenta. 2018. №m 1. C. 13–16 (In Russian).
14. Benabdallah N., Scheve W., Dunn N., Silvestros D. et al. Practical considerations for quantitative clinical SPECT/CT imaging of alpha particle emitting radioisotopes. Theranostics. 2021. V. 11. № 20. P. 9721–9737.