David Long, MD
No relationships to disclose.
Radiation and Cancer Physics
SS 01 - Physics 1 -Best of Physics
Purpose/Objective(s): 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. We hypothesize that patients with worse liver function and/or prior liver directed therapy (LDT) may derive a larger benefit from functional liver image-guided hepatic therapy (FLIGHT) compared to standard planning due to increased heterogeneity in liver function.
Materials/Methods: This study included patients at a single institution who underwent HIDA prior to SBRT. Two plans, standard and FLIGHT, were generated. FLIGHT beam arrangements and plans were optimized with priority given to avoid higher-functioning liver as defined by HIDA. The planning goal was to increase the functional residual capacity of the liver receiving <15 Gy (FRC15HIDA), with a >5% improvement considered significant. The following dosimetric endpoints were compared for FLIGHT vs. standard plans using paired t-tests: FRC15HIDA, mean liver dose, effective uniform dose (EUD), and functional EUD (FEUD). Pearson correlation was used to evaluate whether improvements in FRC15HIDA were associated with baseline Child-Turcotte-Pugh (CTP), global HIDA, and/or liver/planning target volume (PTV) ratio. Dosimetric improvements in CTP A vs. B patients and those with vs without prior LDT (surgery, SBRT, or catheter-based therapies) were compared using independent t-tests.
Results: Standard and FLIGHT plans were created for 33 patients, including 6 who are enrolled on a prospective FLIGHT trial. Compared to standard planning, FLIGHT improved FRC15HIDA, mean liver dose, EUD, and FEUD (p≤0.001); 12 had >5% improvement in FRC15HIDA (mean 4.7%, range -3.8-20.2%), and 24 had >5% improvement in mean liver dose. The improvement in FRC15HIDA were not correlated with CTP or global HIDA (p>0.1). The improvement in CTP A (n=20) vs B (n=13) was 5.5% vs 3.4% (p=0.347), HIDA ≤3.0%/min/m2 (n=20) vs >3%/min/m2 (n=13) was 3.7% vs 6.2%, and prior LDT (n=19) vs no LDT (n=14) was 6.1% vs 3.6% (p=0.252). Liver/PTV correlated with FRC15HIDA improvement (r= -0.353, p=0.044): those with vs without ≥5% improvement had liver/PTV 18.1 vs 37.0 (p=0.009). The improvement in mean liver dose in CTP A vs B was 14.9% vs 8.8% (p=0.073).
Conclusion: FLIGHT with HIDA led to improvements in all analyzed dosimetric parameters. There was individual variation in the extent of benefit based on regional variations in liver function. Patients with worse baseline liver function as assessed by CTP and HIDA and those with prior LDT did not derive a significantly larger benefit from FLIGHT planning suggesting that modifications in addition to FLIGHT may be necessary to increase the therapeutic ratio in patients at high risk for toxicity. Patients with lower liver/PTV ratios derived larger benefit in FRC15HIDA suggesting that consideration of the function of the remnant liver in this population may be important.
No relationships to disclose.
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