Abstract:
Prostate cancer remains a significant cause of cancer morbidity and mortality in men
worldwide accounting for the second-highest incidence of all cancers in males. A
disproportionate incidence, morbidity and mortality of prostate cancer have been reported
in black males than their white counterparts however very little is known of their imaging
differences when presenting with biochemical recurrence. The imaging modalities employed
in cancer staging (computed tomography, magnetic resonance imaging, bone scan and
positron emission tomography) have been under debate due to their varying sensitivities. The
prostate bed is the most common site of early recurrence of prostate cancer. The currently
used PSMA ligands (68Ga-PSMA and 99mTc-PSMA) undergo early urinary clearance resulting in
interfering physiological activity within and surrounding the prostate. This can result in sites
of cancer recurrence being obscured. 18F-PSMA-1007 has an advantage of delayed urinary
clearance thus the prostate region is reviewed without any interfering physiological activity.
There however is limited data on the diagnostic performance of 18F-PSMA-1007 in early
biochemical recurrence.
To our knowledge we were the first to describe the differences in 68Ga-PSMA imaging findings
between black and white prostate cancer patients with biochemical recurrence. We found a
significant correlation between PSA values and the diagnostic performance of 68Ga-PSMA
imaging in both groups. However there was no significant difference in the detection rate,
distribution pattern and the median number of lesions between the two racial groups
suggesting that the tumour burden and growth rate of androgen dependent prostate cancer
may be similar in both races.
We also found 68Ga-PSMA to be superior to bone scan in the assessment of skeletal
metastases in the initial staging of high-risk prostate cancer, demonstrating a higher detection
rate and specificity, indentifying marrow and lytic skeletal metastases thath had been missed
by bone scan.
To our knowledge we were also the first to conduct a head to head comparison of 68Ga-PSMA
and 18F-PSMA-1007 in this thesis. Though limited by a small number of patients, 18F-PSMA-1007 detected more recurrence sites than 68Ga-PSMA. 18F-PSMA-1007 demonstrated a
sensitivity, specificity, positive and negative predictive value of 88.9%, 100%, 100%, and
92.3% respectively while 68Ga-PSMA-11 demonstrated sensitivity, specificity, positive and
negative predictive value of 44.4%, 83.3%, 80%, and 66.6% respectively.
In our thesis, 18F-PSMA-1007 performed equally to other reported PSMA PET agents when
compared with a similar cohort of patients with biochemical recurrence and low PSA value.
PSA doubling time proved significantly related to the detection rate of 18F-PSMA-1007 whilst
no significant relationship was seen with PSA velocity. We found the optimal PSA cut-off value
of 1.26ng/ml to identify biochemical recurrence.
