Background: The identification of prostate cancer by PET/CT imaging of the Prostate-Specific Membrane Antigen (PSMA) has achieved significant relevance in recent years. Hybrid PET-CT imaging with 68Ga-PSMA ligand can reveal lesions indicative of prostate cancer with superior contrast. The aim of present study was “to evaluate the role of 68Ga labelled Prostate-Specific Membrane Antigen (PSMA)ligand hybrid PET/CT in primary & recurrent carcinoma prostate for lesion characterisation, lymph node involvement & skeletal & liver metastases”. Methods: The prospective study was conducted at a large tertiary centre during the period of June 2015 to January 2016 among 100 male patients with a clinical suspicion or diagnosis of prostate cancer. Radiolabeling of PSMA ligand with 68Ga is done using on-site commercially available 68Ge/68Ga generator (itg). Image analysis was done & results were analyzed using SPSS version 25.0. Results: For the study, 100 male patients with a median age of 69 years (range: 37-90 years) were chosen. All images showed good resolution and the lesions had great target-to-background ratio. Thirty-two patients were referred for clinical suspicion, twenty-four for initial staging, & forty-four for examination of recurrence. 16 patients (50%) out of 32 with a clinical suspicion of PCa had focused, strong uptake in the prostate gland that was indicative of the disease. Of the 24 individuals with PCa who were referred for first staging, 24 out of 24 (100%) had abnormal prostate gland uptake. Ninety-nine percent of the 44 PCa patients who had a clinical suspicion of recurrence displayed involvement of the disease site. The sensitivity, specificity, positive predictive value, negative predictive value, & overall accuracy of the 68Ga-labeled PSMA-ligand PET/CT were 95.6%, 100%, 100%, 50%, & 97.6%, respectively. Conclusion: 68Ga-PSMA hybrid PET/CT showed accurate detection of initial & recurrent prostate cancer lesions. Patients with suspected PCa, initial staging, restaging, & recurrence showed excellent contrast in primary lesion identification & lymph node, skeletal, & liver metastasis.
Prostate cancer is the most prevalent tumour among males globally, with a rising incidence observed in recent years [1]. The incidence of PCa in India ranges from 3.38-5.39%.[2] Tumour recurrence or residual presence following prostatectomy, radiation, or other local treatment modalities poses a significant challenge in the management of prostate cancer. Typically, post-therapeutic recurrence following prostatectomy or external beam radiation therapy is identified by prostate-specific antigen (PSA) levels of > 0.2 ng/mL in two consecutive tests, referred to as biochemical recurrence[3].
Morphologic imaging approaches demonstrate significant limitations: sensitivity for detecting local recurrence ranges from 25% to 54% with transrectal ultrasonography or CT, & is substantially enhanced with functional MR imaging methods [4,5]. The sensitivity for detecting lymph node metastases with CT or MR imaging is reported to range from 30% to 80% [6]. Ultra-small iron oxide particles have demonstrated efficacy; nevertheless, they have yet to receive approval from regulatory bodies[7].
Prostate-specific membrane antigen (PSMA) is a type II integral membrane glycoprotein found in various tissues, including the prostate, kidney, small intestine, & both the central & peripheral nervous systems. [8, 9] PSMA is highly expressed in the human prostate, with levels exceeding those in most other tissues by a factor of one hundred. In cancer, its expression is elevated & it has been identified as the second-most upregulated gene in prostate cancer, with an increase of 8- to 12-fold compared to noncancerous prostate tissue[10]. This elevated expression is being pursued as a target for therapeutic & imaging applications. Recently, labelling protocols have been established to tag PSMA ligands with 68Gallium (68Ga), rendering them appropriate for PET/CT imaging.
The identification of prostate cancer lesions by PET imaging of the Prostate-Specific Membrane Antigen (PSMA) has achieved significant therapeutic relevance in recent years. Hybrid PET-CT imaging with 68Ga-PSMA ligand can reveal lesions indicative of prostate cancer with superior contrast. 68Ga-PSMA PET/CT shown improved efficacy in identifying prostate cancer at low PSA levels, attributed to its high sensitivity & specificity, as well as its ability to present lymph nodes with enhanced contrast compared to 18F choline-based PET/CT. [11]
Aim Of The Study
The aim of present study was “to evaluate the role of 68Ga labelled Prostate-Specific Membrane Antigen (PSMA)ligand hybrid PET/CT in Primary & Recurrent Carcinoma Prostate for lesion characterisation, lymph node involvement & skeletal & liver metastases”.
The prospective study was conducted at a large tertiary centre during the period of June 2015- January 2016. Ethical clearance was taken from ethical committee of the centre.
A total of 100 male patients with a clinical suspicion or diagnosis of prostate cancer having any of the following characteristics were included in the study.
Study Procedure
In our centre, radiolabelling of PSMA ligand with 68Ga is done using on-site commercially available 68Ge/68Ga generator (itg) & synthesis module as per standard operating procedure supplied by the manufacturer & there was no need for a cost-intensive cyclotron. (Figure 1).No fasting or special patient preparation was required prior to the study. Dose of 3-4mci 68GaPSMA is injected intravenously. The tracer was well tolerated. Whole body PET imaging & non contrast CT scan (Hybrid PET/CT) was done on 6 slice PET-CT machine one hour after injection.
Early imaging is possible with 68GaPSMA’s short half-life (68 minutes), good labelling chemistry, quick background clearance, & high-resolution PET pictures.
Analysis of images: Software & a Siemens workstation were used for image analysis. When at least one focus of anomalous strong uptake was seen, as determined by eye inspection and/or SUV measures, the scan was considered positive, indicating active disease or recurrence/relapse. PCa is favoured by focally high PSMA overexpression or avidity in the prostate gland. Severe avidity in the liver, skeleton, & lymph nodes indicates metastases. The liver, kidneys, spleen, colon, bladder, & salivary & lacrimal glands all exhibit normal physiological uptake.
Statistical analysis
Version 25 of the Statistical Package for Social Sciences (SPSS) was used for data management & analysis. When appropriate, means, standard deviations, & ranges were used to summarise numerical data. Numerical values & percentages were used to display categorical data. The information was collected, analysed, & arranged. Using accepted standards, the hybrid PET/CT’s sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), & accuracy in identifying prostate cancer were calculated.[12]
For the study, 100 male patients with a median age of 69 years (range: 37-90 years) were chosen. All images showed good resolution and lesions had a great target-to-background ratio. As seen in graph 1, 32 patients were referred for clinical suspicion, 24 for initial staging, & 44 for examination of recurrence.
16 patients (50%) out of 32 with a clinical suspicion of PCa had focused, strong uptake in the prostate gland that was indicative of the disease. Since the remaining 16 patients had no aberrant uptake, a biopsy was not performed & they were placed on clinical follow-up. Of the 24 individuals with PCa who were referred for first staging, 24 out of 24 (100%) had abnormal prostate gland uptake. Three patients experienced abdominal lymph nodal metastases, while nine patients experienced pelvic lymph nodal metastases. One of these three patients had adrenal metastases, another had severe mediastinal & skeletal metastases, & a third patient had additional skeletal metastases. Skeletal metastases were detected in one patient. 40/44 (90.9%) of the 44 PCa patients with a clinical suspicion of recurrence displayed involvement of the disease site. Local recurrence in the prostate gland or prostatic bed occurs in 26 out of 44 cases. Regional pelvic lymph node metastases were found in 21 of 44 patients. Four patients experienced mediastinal lymph nodal metastases, while six patients experienced abdominal lymph nodal metastases. Skeletal metastases were seen in 21 of 44 patients. Graph 2 illustrates the extensive disease of one patient. [Figure 2-10]
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