br Conclusiones Nuestro estudio encontr una
Conclusiones: Nuestro estudio encontró una alta tasa de detección de enfermedad en estudios PET con
68 Ga-PSMA-11 en pacientes en los que otras técnicas presentaban imágenes dudosas o negativas. Casi un 50% de los pacientes con recurrencia bioquímica de cáncer de próstata y niveles bajos de PSA (<1 ng/ml) tienen enfermedad activa en la PET con 68 Ga-PSMA-11, precisamente un nivel donde otros radiotrazadores tienen un peor umbral de sensibilidad.
Medicina Nuclear e Imagen Molecular. Publicado por Elsevier Espana,˜ S.L.U. Todos los derechos reservados.
Prostate cancer is one of the most frequent cancers in the world, being second in incidence in men and the fifth cause of cancer-related death.1 Imaging studies play an important role in this disease since approximately 20–40% of patients develop biochem-ical relapse2 following primary treatment, and these studies can be used to detect disease and guide decisions regarding the most adequate treatment to be implemented.
The prostate-specific membrane antigen (PSMA) is a glyco-protein of the cell membrane with enzymatic activity in the extracellular domain. However, it is not secreted like the prostate-specific antigen (PSA) but rather remains bound to the membrane.3 PSMA is widely expressed in normal epithelium of the prostate gland and to a lesser extent in other tissues such as the brain, salivary glands, intestines, liver and kidney.4,5 It is expressed in practically all the tumor MitoPY1 of adenocarcinoma of the prostate, even in prostatic neoplasms which develop resistance to androgen deprivation.
For the management of prostate cancer, different molecules labeled with radioactive isotopes have been developed to trace the distribution of this biological target.6 Positive emission tomography (PET) with 68 Ga-PSMA-11 (68 Ga-HBED-CC-PSMA) is a non-invasive imaging technique used in the study of prostate can-cer. 68 Ga-PSMA-11 is a radiotracer based on the labeling of a small glycoprotein inhibitor molecule. Among other similar molecules, the use of 68 Ga-PSMA-11, known as 68 Ga-PSMA, has shown to improve the diagnostic capacity of other radiopharmaceuticals (i.e.:
18 F-fluorodeoxyglucose [18 F-FDG], 18 F-fluorocholine) in the evalu-ation of prostate cancer.7,8 Some authors have described greater contrast in images obtained with 68 Ga-PSMA-11 compared to 18 F-fluorocholine, thereby providing greater capacity of detection and reliability in study interpretation. This may be explained in that, although there are not substantial differences in the maximum standardized uptake value (SUVmax ) in the lesions, there are differences in non pathological tissues.9
The aim of the present study was to evaluate the utility of 68 Ga-PSMA-11 as a complementary diagnostic tool in the detection of prostate cancer by the determination of factors associated with possible positive results in the PET study with 68 Ga-PSMA-11.
Material and methods
We performed a retrospective study of 58 scans carried out in 55 patients with prostate cancer referred for PET/CT due to suspicion of recurrence and in 3 cases in whom PET/CT was indicated to com-plete staging in the initial diagnosis of the disease. All the patients had undergone other imaging techniques for the localization of disease with doubtful or negative results.
Images were obtained by PET with gallium 68 bound to the specific PSMA molecule Glu-NH-CO-NH-lys-(Ahx)-HBED-CC also known as PSMA-11. To obtain the radiopharmaceutical 68 Ga-PSMA-11 a GalliaPharm germanium-68/gallium-68 generator of 1.85 GBq (registry number AEMPS 79102) (Eckert&Ziegler Radio-pharma GmbH, commercialized by Nucliber) was used with
PSMA-11 (GMP) as the precursor (ABX, Advanced Biochemical Compounds). Radiosynthesis of 68 Ga-PSMA-11 was totally auto-mated following a protocol based on the method described by Eder et al.,10 achieving a final radiochemical purity of the radiopharma-ceutical of greater than 97% in all the cases.
All the patients received a dose of 2.2 MBq/kg, the mean dose being 212 MBq. The images were obtained at a mean of 62.6 min after administration in a General Electric Discovery STE4 hybrid PET/CT tomograph. In order to avoid artifacts due to excess uri-nary activity (halo effect) or false positive results due to persistence of activity in the ureters, the standardized procedure11 requests patients to be well hydrated, and furosemide was injected immedi-ately after the intravenous administration of the radiotracer. When the first image showed excessive urinary activity or when genes interfered with correct evaluation of the prostatic bed, prostate or adjacent structures, a delayed acquisition was performed within approximately 3 h after radiotracer administration, with a mean time of image acquisition of 164 min.11