In the past ten years, PCa has made substantial use of 68Ga PSMA PET/CT, a relatively novel hybrid functional imaging technique. Targeting PSMA receptors that are overexpressed (100–1000x) in PCa compared to normal prostate cells forms the basis of 68Ga PSMA PET/CT. Initial research on the biodistribution of 68Ga PSMA PET/CT found that normal prostates express PSMA as indicated by SUV_max [1-4].

In a healthy prostate, reported SUV_max values ranged from 2.5 to 8.8. (16,59). In terms of staging, restaging, response assessment and evaluation of biochemical recurrence in PCa, 68Ga PSMA PET/CT has produced positive findings [5-7].

Aims and Objectives

The present study was done for the Analysis of Receiver Operating Characteristic (ROC) curve based on Standardised Uptake Value Maximum (SUV_max) and biopsy results 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 renal failure

• Patient consent to participate in the study

   

  

   

Figure 1: Study Methodology

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 44 patients 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 and ⁶⁸Ga-PSMA PET/CT were done. Biopsy was done in cases with high clinical suspicion of PCa (Figure 1).

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. Receiver Operating Characteristic (ROC) curves was plotted to assess cut-off values of SUV_max to differentiate between malignancy and non-malignant cases. 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_max of 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).

Figure 2 shows Receiver Operating Characteristics (ROC) curve was plotted between SUV_max value of ⁶⁸Ga PSMA PET/CT and biopsy results with sensitivity (y axis) and 1-specificity (x axis). On evaluation, area under the curve was 0.818. It was found that at cut off value of 10.4 for SUV_max, the sensitivity of ⁶⁸Ga PSMA PET/CT was 75% and specificity was 94.1%. It was observed that median of the SUV_max was same across categories of biopsy.

Figure 2: Receiver Operating Characteristic Curve Drawn based on Standardised Uptake Value Maximum (SUV_max) and Biopsy Results

We obtained a Cut off SUV_max value of 10.4 for differentiating benign and malignant cases with a sensitivity of 75 and 94.1% specificity. In study by Woythal et al. [8], they evaluated 31 patients who underwent radical prostatectomy. A SUV_max cut off of 3.5 yielded a sensitivity of 87% and specificity of 97%. They took only biopsy proven cases of PCa in their series and calculated cut-off on basis of IHC. Our results are significantly different from them. In our study, many patients with no evidence of malignancy had SUV_max higher than 3.5. This may be due to different methodology used to arrive at the cut-off as they studies only biopsy proven PCa cases and had no benign cases in their series. They measured normal SUV_max values from normal appearing prostate adjacent to the lesions.

The present study concluded that SUV_max cut-off of 10.4 on ⁶⁸Ga PSMA PET/CT can detect PCa with a sensitivity of 75% and specificity of 94.1%.

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