Establishing a Correlation Between Pre-treatment CT Perfusion Parameter Values and Post-treatment PET/CT Dosimetry to Aid in Tumor-specific Y-90 Radioembolization Treatment Planning for Hepatocellular Carcinoma

The overreaching goal of this line of research is to establish a methodology to produce patient and tumor specific treatment planning for Yttrium-90 radioembolization of hepatocellular carcinoma (HCC). The proposed project will facilitate the collection of preliminary data to support a larger study to more fully establish the relationship between tumor perfusion parameters and delivered radiation dose. Y-90 radioembolization delivers millions of small resin or glass beads attached to or containing (depending on the product) the beta emitting radioisotope of Yttrium. These beads are injected into the patient's hepatic artery during an interventional radiology procedure. The beads are pushed into the hepatic vasculature system by pulsatile flow and eventually become lodged, due to their finite size, in the microvasculature of the liver and tumor and deliver the radiation dose from the high energy beta particles (average energy 0.94 MeV) released during the radioactive decay (half life of 64 hours) in a highly local (~2.5 mm range) manner. The beads are permanently embedded in the vasculature and the radioactivity eventually decays to background.

Current practice is to calculate and deliver an average liver lobe radiation dose based on either the lobar volume or the patient's body surface area. However, because of the hypervascular nature of HCC lesions, the tumors receive a greater proportion of the beads than the healthy liver parenchyma and hence are assumed to receive radiation doses well above that of calculated average liver dose and the dose to the normal liver. Due to the differing vascularity and characteristics of tumors and patients, each Y-90 treatment does not deliver the same dose to the tumor. A less vascular tumor may receive substantially less radiation than a more vascular one which affects the tumoricidal efficacy of the treatment and ultimately the patient's final outcome. New techniques using Positron Emission Tomography (PET)/CT following Y-90 treatment allow for retrospective dosimetry to determine the actual dose delivered to the tumor. However, no methodology exists to plan the dose to be delivered to the tumor prior to the treatment.

This research aims to collect preliminary data to begin to establish a prospective method to use Computed Tomography (CT) perfusion studies of the liver to calculate the expected dose to the HCC lesions and the normal liver based on the blood flow and blood volume. This goal will be achieved by prospectively collecting CT Perfusion studies prior to Y-90 radioembolization treatments and PET/CT immediately following treatments. The relationship between the perfusion parameters representing the vascularity of the lesions and the normal liver and the post treatment PET/CT dosimetry will be established by this line of research. The hypothesized correlation between the perfusion parameters and the tumor dose as established by PET/CT will allow for patient and tumor specific treatment planning ensuring that the appropriate tumoricidal radiation dose is reliably delivered.