br Discussion br The importance of PET with Ga PSMA
The importance of PET with 68 Ga-PSMA-11 lies in the overex-pression of PSMA (100–1000 fold) in almost all prostatic tumors. Only 5–10% of primary prostate cancer lesions present a negative PSMA.14
Clinical data and study characteristics.
BMI: body mass index; CHT: chemotherapy; RT: radiotherapy; PSAdt: prostate-specific antigen doubling time.
Fig. 2. Territories involved in PET. Localization in a single territory much more fre-quent in patients with low PSA values (<1 ng/ml) as well as PSA values greater than 1 ng/ml.
Although some studies support the potential utility of PET with 68 Ga-PSMA-11in the initial staging of prostate cancer,15 at present the main indication for this technique is the detection of disease in biochemical recurrence.12 Therefore, except for 3 cases in this retrospective study, the indication of PET with 68 Ga-PSMA-11 was the localization of disease in patients with biochemical recurrence following the initial radical therapy.
The importance of the results obtained in delayed acquisition is that one of the difficulties of evaluation with this radiotracer is physiological urinary elimination.16 Delayed studies were more frequently performed in case of doubt as to the presence of dis-ease when no extraprostatic lesion was detected. The result of PET with 68 Ga-PSMA-11 showed lesions adjacent to the blad-der compatible with tumor recurrence in 31.6% of the patients who underwent delayed acquisition. Although this was not sys-tematically performed in the patients included in this study and was not specifically analyzed, it was found that images delayed 3 h improved the diagnostic capacity of the technique in these patients17 (Fig. 4).
There are reports of cases of unspecific uptake in the sympa-thetic cervicothoracic, celiac and sacral Veratridine node chains which make interpretation difficult.13 In our series significant uptake was not detected in these localizations in the patients with patholog-ical findings in the iliac or retroperitoneal lymph node chains. In the 2 cases showing supradiaphragmatic involvement, this was accompanied by extensive retroperitoneal, retrocrural and medias-tinic involvement. Therefore, despite the less frequent localization, this is considered to be concurrent with disease extension without performing specific studies for verification.
With regard to the PSA values, these are of special relevance after radical surgery (prostatectomy) since an elevation in PSA values between 0.01 and 0.1 ng/ml presents a 67% probability of relapse, while a value greater than 0.1 ng/ml raises the risk to up to 90%.18 A patient is considered to have biochemical recurrence when the
Fig. 3. Distribution of results of PET/CT with 68 Ga-PSMA according to PSA levels. Negative and positive results in the PET/CT study within different ranges of PSA values expressed in ng/ml.
Perirectal 5 (9)
N.o territories involved
Visceral metastasis 1 (2)
a Includes lesions with greatest uptake.
Multiple logistic regression analysis with pathological PET as dependent variable.
Variable Score p
PSA: prostate specific antigen; OR: odds ratio; CI: confidence interval.
Fig. 4. Early-delayed study. Gleason 6 prostate adenocarcinoma treated with external radiotherapy. Right pathological prostatic foci in which the delimitation improved in the delayed study. Bottom row: image at 60 min; upper row: image at 180 min.
PSA value is greater than 0.1 ng/ml, with treatment being adminis-tered even in the absence of accurate knowledge of the localization and extension.19 Our results show microspores PET with 68 Ga-PSMA-11 has a high lesion detection capacity even in patients presenting biochemical recurrence with PSA values still within an incipient phase since 48% of the patients with a PSA value < 1 ng/ml were pos-itive, similar to the frequency described by Verburg et al. (44%)19 and Medina-Ornelas et al. (47%),20 but greater than that reported by Soydal et al. (21%).21 To the contrary, 18 F-fluorocholine has a more limited detection capacity with PSA values < 2 ng/ml.7,22,23 In a recent study, PSA levels were related to the tumor mass detected by PET with PSMA.20
In relation to the PSAdt, in our study the values were a mean of 12.97 months with a median of 6.75 months in the pathological studies, being a value similar to that obtained with