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Location: Marriott Marquis
Location: Marriott Marquis
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Main Session

QP 06 - Phys 9: Imaging for Planning

1035 - Precision Radiotherapy for Hepatocellular Carcinoma: Exploring the Clinical Utility of Functional Liver Avoidance Planning

Tuesday, October 1, 2024
8:30 AM – 8:35 AM ET
Location: Room 152
A. A. Yorke1, M. Nyflot1, S. Apisarnthanarax1, P. A. Sponseller2, and S. R. Bowen1; 1Department of Radiation Oncology, University of Washington/ Fred Hutchinson Cancer Center, Seattle, WA, 2University of Washington School of Medicine, Fred Hutch Cancer Center, Department of Radiation Oncology, Seattle, WA

Purpose/Objective(s): Functional liver avoidance planning has the potential to mitigate radiation-induced hepatotoxicity for patients with hepatocellular carcinoma (HCC), but it is unclear if all patients benefit from this approach. We assessed the utility of functional liver avoidance planning to meet clinical constraints and reduce dose to functioning liver tissue. Materials/

Methods: Twenty patients (52-83 years, 6/20 female) with varying degrees of liver cirrhosis (Child-Pugh scores A5-B9) underwent [99mTc] sulfur colloid SPECT/CT imaging with generation of functional liver volumes (FLV) at 30%max thresholds, and FLV were co-registered onto planning CT scans. Half of patients received prior liver directed therapy (LDT). VMAT-SBRT (5 fx, 5 CP-A, 5 CP-B/C) conventional plans were optimized following ASTRO consensus guidelines and those that did not meet published functional liver dose constraints (FLV mean, FLV V20) were re-optimized for functional liver avoidance and scaled to the same target dose coverage. Scanning proton beam therapy (PBT) plans were similarly generated for hypofractionated regimens (15 fx, 5 CP-A, 5 CP-B/C). We characterized the associations between clinical characteristics and the probability of FLV re-optimization and correlations with FLV dose reduction.
Results: CP-A SBRT conventional plans met all clinical and functional liver dose constraints, while 40% of CP-A PBT plans, 40% of CP-B/C SBRT plans, and 80% of CP-B/C PBT plans required re-optimization for FLV dose constraints. Relative to conventional plans, FLV replans reduced the FLV mean dose and FLV V20 by a median of 13% (2%-30%) and median of 4% (1%-10%), respectively. Increasing likelihood of prior LDT correlated with a decrease in FLV re-optimization frequency (Spearman R -0.95, p=0.05). This is reflected in CP-A SBRT patients requiring fewer functional liver avoidance replans (80% prior LDT, 0% FLV replans) compared to CP-B/C PBT patients (10% prior LDT, 80% FLV replans). Furthermore, SBRT patients had significantly smaller tumor volumes than PBT patients (12cc vs. 65cc, p=0.03).
Conclusion: We have investigated the clinical utility of functional tissue avoidance in different groups of patients with HCC as a planning strategy to preserve liver function and mitigate hepatoxicity. CP-A SBRT patients with smaller tumors were least likely to require functional avoidance planning, whereas CP-B/C patients receiving PBT were most likely to benefit. This may be linked to cirrhotic liver spatial heterogeneity, tumor size, and strict dose constraints to mitigate high risk of hepatotoxicity. Selective functional avoidance planning is effective at reducing functional liver doses and should be considered in future clinical trial designs.