2245 - Contrast-Enhanced Adaptive Stereotactic Body Radiotherapy (SBRT) for Multiple Hepatic Lesions with One Isocenter Using the Ethos Platform

03:00pm - 04:00pm ET

Poster Hall - Exhibit Hall A

Screen: 30

POSTER

Presenter(s)

Kim Vo, DO, MS - City of Hope Comprehensive Cancer Center, Duarte, CA

K. Vo¹, B. Liu², R. Zovigian³, J. Zhu², S. N. Lim², R. J. Beatty³, A. Liu², T. M. Williams¹, and Y. Liu¹; ¹City of Hope, Duarte, CA, ²Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, ³City of Hope National Medical Center, Duarte, CA, United States

Purpose/Objective(s): Stereotactic body radiotherapy (SBRT) for multiple hepatic metastases is technically challenging due to interfraction variability in tumor and organ-at-risk (OAR) positioning along with difficulty in daily tumor alignment. We evaluated the feasibility of contrast-enhanced adaptive radiation therapy to improve target coverage, lower dose to OARs, and increase the overall therapeutic ratio.

Materials/Methods:

Five consecutive patients with multiple liver lesions (13 lesions total) were treated with the goal prescription dose of 30-50 Gy in 5 fractions to each lesion using contrast-enhanced Ethos adaptive treatment between December 2025-February 2026. Treatment was performed every other day. For each treatment, contrast injection was performed 30 seconds prior to CT scanning on Ethos to aid in tumor visualization for adaptive planning. Each adaptive plan underwent physician contour review and physics plan verification prior to delivery. Dosimetric parameters, including GTV coverage (D95%, V100%), PTV coverage (D95%, V100%), and OAR doses (Dmax of duodenum, small bowel, large bowel, stomach, common bile duct, and esophagus and mean liver-GTV) were compared between scheduled and adaptive plans using Wilcoxon signed-rank test. Constraint violations were analyzed using exact McNemar testing (discordant pairs). Toxicity was assessed prospectively during on-treatment visits and early follow-up using CTCAE v5.0.

Results: Five patients with 2-4 liver lesions each (13 total lesions) were treated with 1 isocenter over 5 treatment sessions. Adaptive plans improved mean PTV V100% coverage from 77.9% (Range: 35.3%-96.3%) to 94.6% (Range: 73.4%-99.1%) (+16.7%; p<0.001). Fractions meeting =95% PTV coverage increased from 1/65 (1.5%) to 50/65 (76.9%). 100% of scheduled radiation plans had at least one OAR constraint violation with duodenum being the most commonly overdosed OAR, while with adaptive plans, there were no OAR violations. All 5 patients completed treatment without interruptions. Grade 1-2 toxicities included fatigue 3/5 (60%), anorexia 2/5 (40%), and nausea 1/5 (20%), and were managed with standard supportive care. There were no reported Grade =3 toxicities.

Conclusion: Contrast-enhanced daily Ethos adaptive SBRT allowed for successful targeting of multiple liver metastases with 1 isocenter, significantly improving target coverage while meeting all OAR constraints. This approach was well-tolerated with no grade 3 or higher toxicities during treatment.