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].

Higher serum Prostate Specific Antigen (PSA) levels are indicative of high suspicion of PCa. Screening using serum PSA levels helps in early detection of PCa but it can be false positive in prostatitis and non-cancer related benign prostatic hypertrophy. Reported sensitivity and specificity of serum PSA is 86% and 33%, respectively [8,9].

The measurement of SUVmax values of lesions in 68Ga-PSMA PET/CT provides information of proliferative cellular activity and cellularity in the tumor, as well as a reflection of the general tumor response to treatment. The SUVmax evaluated by PET/CT may reflect the clinical condition in patients with prostate carcinoma and possibly correlate with PSA levels [10].                

Aims and Objectives

To correlate between S. PSA levels and SUVmax on 68Ga PSMA PET/CT in Prostate Cancer Patients

Study Design

Prospective pilot study.

Place of Study

This study has 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 renal failure

• Patient consent to participate in the study

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 the study

Study Population

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

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.

Figure 1: Study Methodology

Figure 2: Scatter plot between SUVmax (standardized uptake value maximum, x-axis) and PSA (serum prostate specific antigen, y axis)

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. To see correlation between different variables, Pearson or Spearman correlation coefficient was calculated, depending on data being analyzed. 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. Out of the total 44 patients, 33 patients with complaints of LUTS or raised serum PSA levels underwent biopsy. All these patients were also subjected to 68Ga-PSMA PET/CT acquisition and SUVmaxof the lesions were measured for quantitation.

The median and IQR (interquartile range) of S. PSA levels in this group of 33 patients was 13.4±13.9ng/mL. The median and IQR of the SUVmax was 7.5 and 12.85. On statistically evaluation, no significant correlation was observed between S. PSA and SUVmax (r = 0.316, p = 0.073). Figure 2 shows the scatter plot of PSA levels and SUVmax values.

The higher the SUVmax levels, the greater the likelihood of neoplastic disease. Therefore, if a high PSA value predicts a higher SUVmax, it is good to know which patients are more likely to have metastases and which patients benefit from a 68Ga-PSMA PET/CT scan.

In our study, on statistically evaluation, no significant correlation was observed between S. PSA and SUVmax (r = 0.316, p = 0.073). but opposite to our study, a positive correlation was shown between the PSA blood levels and SUVmax values of 68Ga-PSMA PET/CT in prostate carcinoma lesions (r = 0.47; p = 0.01) in the study done by Erika S. Fajardo-Ordóñez et al. [10].

The present study concluded that there was no significant correlation was observed between S. PSA and SUVmax in prostate cancer patients.

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10. Fajardo-Ordóñez, E.S. et al. “Correlación entre los Niveles de Antígeno Prostático Específico y los Valores de SUVmáx en Pacientes con Cáncer de Próstata Evaluados con 68Ga-PSMA PET/CT.” Revista de Medicina del Instituto Mexicano del Seguro Social, vol. 19, no. 4, 2020, pp. 286–296.