3112 - The Role of Tumor Location and Motion in Local Failures after Radiation Therapy for Hepatocellular Carcinoma

P. Yeh¹, K. Thonglert², C. Grassberger¹, Y. He¹, M. Nyflot¹, S. R. Bowen¹, and S. Apisarnthanarax¹; ¹Department of Radiation Oncology, University of Washington/ Fred Hutchinson Cancer Center, Seattle, WA, ²Division of Radiation Oncology, Department of Radiation, Faculty of Medicine, Chulalongkorn University, King Chulalongkorn Memorial Hospital, Bangkok, Thailand

Purpose/Objective(s): Prior studies on local control with stereotactic body radiation therapy (SBRT) and proton beam therapy (PBT) for hepatocellular carcinoma (HCC) have primarily concentrated on tumor and treatment related factors, such as tumor size and dose, with inconsistent results. We investigated the less-studied spatial and motion-related factors in patients with HCC who developed local failures after SBRT and PBT. Materials/

Methods: A single-institution retrospective analysis was conducted to review 186 consecutive HCC patients treated with SBRT or PBT from 2013 to 2020. Patients with local failures as a component of any pattern of failure were included; those treated for non-parenchymal liver lesions were excluded. Data on patient and tumor characteristics, treatment modality (SBRT vs. PBT), tumor location relative to liver anatomical landmarks (subphrenic or other liver-tissue interfaces), and motion management strategies (free-breathing, abdominal compression, or breath-hold) were gathered. Descriptive analyses were utilized to assess these variables in relation to local failure occurrences.
Results: A total of 17 patients with local failures were identified for analysis. Of these patients, the median age was 71 years, 65% were male, 47% had BCLC stage A disease, 82% had Child-Pugh A liver function, and median tumor diameter was 7.4 cm. The median time to local failure was 14 months. The majority of patients (n=12) were treated with PBT (median dose 63.5 Gy in 15 fractions), and 5 were treated with SBRT (median dose 40 Gy in 5 fractions). Nearly all local failures (94%, n=16) occurred in patients with tumors at subphrenic (65%, n=11) or other liver-tissue interface locations (29%, n=5). Among these patients, most (n=12) had no or limited motion mitigation during treatment (free breathing, n=8; abdominal compression, n=4). Overall, patients with tumors in the subphrenic location treated with PBT and limited motion management represented the most dominant cohort (n=8).
Conclusion: Tumors near liver-tissue interfaces, particularly when treated with PBT and without motion management, are commonly observed in HCC local recurrences. These hypothesis-generating findings suggest that p</span>roximity to liver-tissue interfaces, treatment modality, and motion management should be factors considered when evaluating for local recurrence in HCC tumors. These results underscore the need for further investigation to explore these associations and their underlying mechanisms more deeply.

Abstract 3112 – Table 1

	Subphrenic			Other liver-tissue interface			Neither
	Free breathing	Abdominal compression	Breath-hold	Free breathing	Abdominal compression	Breath-hold	Free breathing	Abdominal compression	Breath-hold
SBRT	1	0	2	0	0	1	1	0	0
PBT	5	3	0	2	1	1	0	0	0