Page 190 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

Response assessment with [18F]DCFPyL and [18F]FDHT for PET quantification of specifically targeted radiotracers (such as [68Ga]/[18F] PSMA, [68Ga]DOTATATE, and [18F]fluorodihydrotestosterone [FDHT](8)), as the distribution volumes of such tracers are mostly limited to tissues that express their specific target (7). Thus, (at fixed tracer dosages) large tumour volumes are more likely to influence tracer availability in plasma for such tracers and using SUV for quantification can become invalid. Clinical illustration To illustrate the sink effect, we hereby present a case of a 72-year old patient with mCRPC who underwent [18F]DCFPyL and [18F]FDHT PET-CT before starting abiraterone treatment, and again after 1 month of treatment (as part of an ongoing IRB-approved prospective study, IRB number 2014.218; the patient provided written informed consent for participation). This patient had been treated sequentially with upfront docetaxel, enzalutamide, and cabazitaxel. Baseline and follow-up PSA levels were 1436 ng/mL and 1936 ng/mL, respectively, indicating progressive disease under abiraterone. 9 Figure 9.1: [18F]DCFPyL PET-CT images of a 72-year old patient with metastatic castration-resistant prostate cancer scanned (A) before and (B) during abiraterone treatment. A PSA rise from 1436 ng/mL to 1936 ng/mL indicated disease progression (one month after treatment start), and an accompanying increase in PSMA-positive disease burden is evident. PET images are shown as maximum-intensity projections. 189