Functional Liver Image-Guided Hepatic Therapy (FLIGHT) with Hepatobiliary Iminodiacetic Acid (HIDA) Scans: Functional Parameters May Predict for Decompensation after Stereotactic Body Radiation Therapy (SBRT)

Abstract

Hepatobiliary iminodiacetic acid (HIDA) scans provide global and regional assessments of liver function that can serve as a functional map for stereotactic body radiation therapy (SBRT) planning. This study sought to demonstrate a dosimetric improvement with functional liver image-guided hepatic therapy (FLIGHT) compared to standard planning using functional dose-volume histograms (fDVHs). We hypothesize that fDVH-based parameters may predict for post-SBRT decompensation and complement blood chemistry-based liver assessments. This study included 17 patients who underwent HIDA scans prior to SBRT for hepatocellular carcinoma (HCC). All SBRT cases were replanned using the FLIGHT technique as follows: (1) baseline HIDA scan was fused to the planning CT (2) contours corresponding to 25-100%, 50-100% and 75-100% of maximum were generated (3) beam arrangements were chosen and plans were optimized with priority given to avoiding higher-functioning liver and to preferentially distribute dose through regions of liver with lower function. The planning goal of FLIGHT planning was to maximize the functional residual capacity of the liver receiving <15 Gy (FRC15HIDA). The following dosimetric endpoints were compared for FLIGHT vs. standard SBRT planning using paired t-tests: FRC15HIDA, mean liver dose, effective uniform dose (EUD), and functional EUD (FEUD). Receiver operating characteristics (ROC) curves were used to evaluate whether baseline HIDA values, standard cirrhosis scoring, and/or dosimetric data predicted post-SBRT clinical decompensation. Decompensation was defined as radiographic or clinical evidence of ascites, hepatic encephalopathy, GI bleeding, HCC not amenable to treatment, or bland portal vein thrombosis. Compared to standard planning, FLIGHT significantly improved FRC15HIDA by a mean of 5.3%, while also significantly improving mean liver dose, EUD, and FEUD (p<0.05 ), although there were considerable interindividual variations in the extent of benefit. Following SBRT, decompensation risk was associated with global HIDA <2.915%/min/m2, FRC15HIDA <2.11%/min/m2, and MELD ≥11 (p<0.05 ). These same global HIDA and FRC15HIDA thresholds were significantly associated with MELD increase ≥2 at 3 or 6 months (p<0.05 ). No other parameters were associated with decompensation [mean liver dose (AUC of 0.467, p=0.841 ), EUD (AUC 0.400, p=0.549 ), FEUD (AUC 0.511, p=0.947 ), baseline liver volume (AUC 0.571, p=0.626 )]. FLIGHT with HIDA-based parameters such as FRC15HIDA may complement blood chemistry-based assessments of liver function and facilitate individualized, adaptive liver SBRT planning.