Imaging / PSMA PET

Question 1

what is PSMA

Answer 1

glycoprotein expressed increased in prostate cancer high grade

Question 2

Lu177 PSMA therapy

radiation dose delivered

Answer 2

Selective tumour targeting

Long half lives mean high doses delivered specifically

> 200Gy to bone lesions and >400Gy to visceral mets

Question 3

tracers used

Answer 3

the majority of published studies used 68Ga-labelling for PSMA PET imaging, but some used 18F-labelling

Question 4

Perera paper SR PSMA sensitivity in BCR 2020 Hofman group
percentage positive scan at psa 0-0.2 and 2 upwards
sensitivity and spec on per node analysis

Answer 4

In BCR: sensitivity increased with PSA value
For PSA categories 0–0.19 0.2–0.49, 0.5–0.99,1–1.99, and over 2 ng/ml, the percentages of positive scans were 33%,45%, 59%, 75%, and 95%, respectively
. On per-node analysis, high sensitivity(75%) and specificity (99%) were observed.

Question 5

PSMA pet vs MRI primary staging

Answer 5

SR and MA of 13 studies
68Ga PSMA higher sensitivity and comparable specificity
Sens 0.65 and Spec 0.94 vs 0.41 and 0.92 for MRI

Question 6

spatial resolution limit LN for CT

Answer 6

In summary, PSMA PET/CT is more appropriate in N-staging as compared to MRI, abdominal contrastenhanced CT or choline PET/CT; however, small LN metastases, under the spatial resolution of PET (~5 mm), may still be missed.

Question 7

increased sens of psma pet vs ct and bone scan for primary staging ln mets and bone mets

Answer 7

Reliable detection of pelvic lymph node metastasis or occult distant metastasis can be improved by PSMA PET imaging.
Gallium-68 PSMA PET–CT has a 27% greater accuracy, and higher sensitivity and specificity, than conventional imaging with CT and bone scans to reveal otherwise occult metastasis in men with high-risk disease

Question 8

bone scan positivity

Answer 8

2.3% if PSA <10
5.3% PSA 10.1 to 19.9
16% in PSA 20.0 to 49.9