68Ga PSMA PET/CT is a relatively new hybrid functional imaging modality which has been extensively used in PCa in the last decade. The basis of 68Ga PSMA PET/CT is targeting of PSMA receptors which are over expressed (100-1000x) in PCa as compared to normal prostate cells. Initial studies on bio distribution of 68Ga PSMA PET/CT reported tracer uptake (PSMA expression) in normal prostate as measured by SUVmax. [1-4]

The reported SUVmax values in a normal prostate ranged from 2.5-8.8. 68Ga PSMA PET/CT has shown encouraging results in staging, restaging, response assessment and evaluation of biochemical recurrence in PCa.[5-7]

Aims & Objectives

The present study was done with the objective of  Quantitative Analysis of  ⁶⁸Ga-PSMA PET/CT in Prostate Cancer Patients

Study Design: Prospective pilot study

Place of Study: This study have been conducted at the Department of Nuclear Medicine, PGIMER Chandigarh in collaboration with the Department Urology, Radiodiagnosis and Histopathology, PGIMER, Chandigarh

Period of study: The study was done during the period between January, 2018 and June, 2019.

Inclusion Criteria

• Patients having suspicion of carcinoma prostate on clinical assessment and/or raised serum PSA levels(>4ng/ml).

• Patient not suffering from bleeding diathesis or renalfailure.

• Patient consent to participate in thestudy.

Exclusion Criteria

• Patient with prior diagnosed PCa or who underwent prostatic biopsy priorto⁶⁸Ga-PSMA PET/CT and mpMRI

• Patients with deranged renal function tests orcoagulogram

• Patient refused to participate in thestudy

Study Population: A total of 44patients suspected for PCa on the basis of clinical assessment and/or raised PSA were recruited for the study.

Figure-1: Study Methodology

Patients suspected for prostate adenocarcinoma and/or serum PSA levels >4ng/ml and willing to participate in the study were recruited. Study was approved by Institutional Ethics Committee, PGIMER Chandigarh. Written informed consent was obtained. After clinical assessment, mpMRI and⁶⁸Ga-PSMA PET/CT were done. Biopsy was done in cases with high clinical suspicion of PCa.

Statistical Analysis

Qualitative variables are described using number and percentages. Normally distributed continuous quantitative data is described using mean and standard deviation. Skewed quantitative data is described using median and interquartile range. The normality of data will be checked by measures of Kolmogorov-Smirnov tests of normality. The sensitivity, specificity, NPV and PPV of ⁶⁸Ga-PSMA PET/CT was estimated using a 2x2 table. The statistical analysis was conducted using the IBM SPSS STATISTICS (version 23.0)

In this prospective study, a total of 44 patients suspected to have PCa were recruited on the basis of clinical assessment and serum PSA levels. All patients were subjected to ⁶⁸Ga-PSMA PET/CT acquisition. Out of the total 44 patients, 33 underwent biopsy. The remaining 11 patients did not undergo biopsy after revised clinical assessment based on negative. Therefore, 33 patients underwent ⁶⁸Ga-PSMA PET/CT and biopsy. 

In this study, malignancy was detected in 16/33 (48.5%) patients on biopsy. In 17/33 (51.5%), no evidence of malignancy was noted.

The mean and SD of the injected 68Ga PSMA radioactivity was 2.79 ±0.89 mCi (103.2 ± 32.9MBq). The median time between the injection and scan acquisition was 65 min (IQR 32.5 min). SUV_maxof the lesions were measured for quantitation and the results were compared with histopathological reference standard. 

The median SUV_max for cases with confirmed malignancy (n=16) was found out to be 17.6 (IQR 18.9). Median SUV_max for cases with no evidence of malignancy was 6.3 (IQR 2.80). The difference between the two groups was found to be statistically significant (Mann Whitney U test, P =0.002). Fig. 2 shows box plot comparing SUV_max between the 2 subgroups.

Figure -2: Box Plot showing SUV_max of PSMA in malignant and non malignant lesions

In the present study, PSMA expression measured by SUV_max on ⁶⁸Ga PSMA PET/CT was found to be significantly higher in PCa as compared to benign cases (p <0.002). In our study, median and range of SUV_max of patients with PCa was found to be 17.6 and 2.7 - 39.4. In a study [6] of biopsy proven PCA cases, they found median and range of SUV_max was 11.5 and 2.7 – 66.4.

The present study concluded that SUV_max (PSMA expression) was significantly higher in Prostate cancer cases as compared to benign cases . 

The authors declare that they have no conflict of interest

No funding sources

The study was approved by the PGIMER, Chandigarh

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2. Zhang, J., et al. "Diagnostic Performance of 68 Ga-PSMA PET/CT in the Detection of Prostate Cancer Prior to Initial Biopsy: Comparison with Cancer-Predicting Nomograms." Eur J Nucl Med Mol Imaging 46. (2019), pp. 908-20.

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7. Demirci, E., et al. "Normal Distribution Pattern and Physiological Variants of 68Ga-PSMA-11 PET/CT Imaging." Nuclear Medicine Communications 37. (2016), pp. 1169-79.