First experience of SPECT-CT with the radiopharmaceutical Thallium-199 chloride in diagnosis and assessment of the metastatic spread of lung cancer

Abstract

Introduction. The development and improvement of new tomographic technologies for highly sensitive imaging of lung cancer (LC) is crucial for the early detection of this disease, accurate staging and control of complex therapy.The purpose of the study. To study the possibility of using the radiopharmaceutical (rp) 199TlCl for SPECT-CT imaging of LC.Material and methods. 199TlCl in solution was obtained at the U-120 cyclotron (Efremov Institute of Physics and Technology, Rosatom, St. Petersburg) of the TPU Institute of Physics and Technology by the reaction of irradiation of a metal gold target with alpha particles 197Au(α,2n)199Tl, at an alpha particle energy of 28 MeV, with a 199Tl yield of over 95%, in saline solution. The injected dose of rp was 180–185 MBq in all cases, and the scan was performed in 12–20 minutes after the injection of 199TlCl. The chest SPECT was acquired as 64 planar scans per 360° rotation of the two-detector system, in a 64 × 64 matrix, with a field of view size of 40 × 40 cm, with acquisition of more than 50,000 pulses per frame, with a high-energy high-resolution collimator installed, with an energy peak of 70 keV set at a window width of 20% of the differential discriminator. The axial sections were reconstructed using the back-projection method, taking into account the depth absorption with an absorption constant of 0.12 1 / cm. The contour of the patient's body for this purpose was imported from the CT. CT of chest was carried out immediately after the SPECT, ro the 512 × 512 matrix, with a spatial resolution of 1 mm. No X-ray contrast enhancement was carried-out. All studies were performed using a combined SPECT-CT scanner Simbia T16 (Siemens Medical).We recruited 12 patients with an established diagnosis of non-small cell LC, in everybody the SPECT-CT with 199Tl-chloride was employed to stage the disease. The control group comprised 7 patients who underwent a study with 199Tl-chloride for non-oncological pathology, but the diagnosis was finally rejected.Results. Visually, in SPECT-CT with 199TlCl in patients without tumor pathology, the accumulation in the lungs was close to background, and the image of the mediastinum was due to the normal accumulation of rp to the heart muscle. Ratio “healthy lung/myocardium” was 0.23 ± 0.05 in the control group. For the primary node of LC, this index was 0.62 ± 0.14 (p < 0.02), and for metastatically involved lymph nodes, 0.59 ± 0.16 (p < 0.05). According to the results of the individual picture of SPECT-CT with 199TlCl in LC, 6 patients out of 12 had expanded radiation areas during external gamma therapy.Conclusion. 199TlCl has a high affinity to the LC tumor tissue and shows high accumulation both to the primary and to metastatic LC foci. Routine use of SPECT-CT with 199TlCl in LC makes sence, both in the primary diagnosis and for the staging of the disease. It is necessary to continue the study of 199TlCl as rp for both ptimary diafnostic imagung of LC and also for the follow-up control of therapy.