68Ga-PSMA I&T PET/CT for primary staging of prostate cancer

[tango65]

17% of the patients had distant metastases and 21% positive lymph nodes.

ncbi.nlm.nih.gov/pubmed/315...

[timotur]

It looks like a test-positive PSMA scan has only about 2/3 chance of being correct.

In correlation with histopathology, calculated per-region sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for detection of lymph node metastases were 35.0%, 98.4%, 63.6%, 95.0%, and 93.0%, respectively.

Positive predictive value is the probability that subjects with a positive screening test truly have the disease.

[tango65 in reply to timotur]

I believe that refers to lymph nodes metastases and not to distant metastases.

[timotur in reply to tango65]

I think it includes bone mets and others...

PSMA-avid lymph nodes were recorded in 17/82 patients (20.7%, 3 with intermediate-risk and 14 with high-risk PCa); distant disease was found in 14/82 subjects (17.1%, 2 with intermediate-risk and 12 with high-risk PCa).

[Hidden in reply to timotur]

how did it define "avid"

[tango65 in reply to Hidden]

Unequivocally avid is considered when the SUV value of the area is around the SUV value of the liver. They do not specifically said the SUV values found in each of the lesions reported in this study. Reporting PSMA PET/CTs is very technical and different places have different criteria.

[Hidden in reply to tango65]

so perhaps that is why they give the liver SUVmax in a PSMA scan, I'm assuming that is what hepatic lobe means, which in my case said:

History of prostate cancer with:

- Focus of increased PSMA uptake in the central mid gland SUV max 3.6 (7-466).

- 4 mm left common iliac lymph node with mild PSMA uptake SUV max 2.3 (7-396).

- 6 mm left para-aortic with mild PSMA uptake SUV max 2.5 (7-367)

SUVmean/max parotid/salivary glands 9.6/11.7 (fused series 7- image 90)

SUVmean/max right hepatic lobe 7.4/9.0 (fused series 7- image 265)

SUVmean/max descending thoracic aorta (level carina) 1.3/1.7 (fused series 7- image 201

whereas the lymph node SUVmax was 2.3. which is just "suspicious." But the way I understand it, when a succeeding scan sees more in that range, the trend is demonstrating that you may have spreading metastasis in the lymph nodes. so I had radiation to the pelvic area as a whole. Which we will see how that goes

[tango65 in reply to Hidden]

I am in a similar situation with a small node, 4 mm with a SUV o f2.4. The nuclear medicine radiologist said that he considered this finding "suspicious" and it did not recommended to proceed with radiation.

They want to wait 6 months and repeat the study.

I already have this problem with a rib with a SUV around 3.5 and the MRI did not show anything wrong in the bone marrow.

I already had 6 PSMA PET/CT and this area in the rib appears and disappears in different scans. When I was at the TUM in Munich, they told me they do not call a metastasis if the SUV is below 4. That was in 2016 and I do not know if they still keep this criterium. They do not use Lu 177 PSMA unless there are lesions with SUVs similar or higher than the liver.

[timotur]

PSMA “avid” in my test was set at a minimum SUV threshold of 3.5, and my LN in question was measured right at the minimum. One RO thought it was a false positive given it’s proximity to the prostate.

[tango65 in reply to timotur]

Here they give some criteria to qualify the findings according to SUV values:

jnm.snmjournals.org/content...

[Justfor_ in reply to tango65]

Useful distinction taken from above mentioned paper:

"For PSMA ligands with liver-dominant excretion (e.g., 18F-PSMA1007), the

spleen is recommended instead of the liver for comparison against

blood-pool and salivary gland uptake".

(...... deleted sentence ...... )

[tango65 in reply to Justfor_]

18F DCFPyl and Ga 68 PSMA are eliminated by the kidney and they have similar liver SUVs. PSMA 1007 is eliminated by the liver and it is a more appropriated ligand to study the pelvis including the prostate

[Justfor_ in reply to tango65]

Thanks for the correction.

[Hidden in reply to timotur]

3.5 seems really low. More like “suspicious”. But it seems to me what the doctors are doing is trying to get ahead of the cancer by calling lower and lower numbers metastasis and then treat it as oligometastatic. I really can’t argue with that tactic.