Parametric PET of Genitourinary Cancer

Metastatic kidney cancer is usually treated with targeted therapy or immunotherapy which is costly and has low response rate. The current standard care is to perform anatomical imaging studies after a few cycles (months) of treatment to evaluate response. This approach exposes many patients to highly toxic, high expensive treatment without any benefit for months and delays initiation of other effective therapies. The goal of this study is to evaluate a parametric PET method that potentially identify response and assess drug efficacy with a few days to weeks of treatment.

Renal cell carcinoma (RCC) is one of the top ten cancer types in the US. One-third of RCCs are metastatic and associated with a poor 5-year survival rate of 8%. Metastatic RCC is usually treated with targeted therapy or immunotherapy which is costly (>$10,000 per month) and has low response rate (<30%). Effective identification of the most appropriate drugs for a patient relies on noninvasive imaging to assess early response to the drugs. However, current practice by anatomical imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) can only assess the response at two months after initialing targeted therapy. This approach exposes many patients to highly toxic, high expensive treatment without any benefit for months and delays initiation of other effective therapies.

The investigators hypothesize that functional perfusion imaging by positron emission tomography (PET) can enable RCC response assessment as early as at 1-2 weeks given that RCC is highly related to angiogenesis and most targeted drugs for RCC are antiangiogenic. However, clinical options for functional renal imaging are very limited. While dynamic contrast-enhanced CT or MRI can be used for perfusion imaging, their use is restricted because 30% of RCC patients have chronic kidney diseases with renal dysfunction and are at higher risk for contrast-induced nephropathy and nephrogenic systemic fibrosis. Existing PET radiotracers (e.g., 15O-water) for perfusion imaging are short-lived and generally unavailable for clinical use. This project explores parametric PET perfusion imaging using the widely accessible 18F-fluorodeoxyglucose (FDG). 18F-FDG PET is conventionally used for metabolic imaging and has been rarely used for imaging kidneys because physiological excretion of 18F-FDG into renal pelvis contaminates image quality for renal tumor assessment. The investigators explore the potential of the metabolic radiotracer 18F-FDG for perfusion imaging by employing four-dimensional (4D: 3D space plus 1D time) dynamic scanning and tracer kinetic modeling, leading to parametric imaging of FDG perfusion kinetics without being affected by 18F-FDG excretion. The parametric PET method can potentially identify RCC response and assess drug efficacy with 1-2 weeks of treatment as compared to 2 months by current anatomical imaging methods.