3450 - Predictors of Pathologic and Radiologic Response in Patients with HCC Treated with SBRT Prior to Transplant

Purpose/Objective(s): Liver directed therapies including TACE, Y-90, and SBRT allow for tumor control and sometimes downstaging in patients who are suitable candidates as bridge to definitive treatment with transplantation. The purpose of this analysis is to investigate predictors of radiologic and pathologic responses in patients who have undergone SBRT prior to transplant.

Materials/Methods: Patients treated with CT based SBRT for HCC followed by liver transplant from 2013-2024 were retrospectively analyzed with post-treatment imaging results, AFP levels, and explant pathology, to determine response to radiotherapy. Radiation treatment parameters including target volumes and doses were collected from the treatment planning software. Complete pathologic response was defined as no viable tumor seen, partial pathologic response was defined as viable tumor and necrosis seen, and no response defined as viable tumor without any necrosis. Complete radiologic response was defined as no arterial enhancement on MRI, partial response was defined as at least 30% decrease in viable lesion, stable disease was defined not progressive or partial disease, and progressive disease was defined as increase of at least 20% in viable lesion. Statistical software was used for data analysis.

Results: Thirty-five patients were treated to 59 lesions with 20% of patients having two separate courses. Patients had a mean age of 61.9 (range 49-73 years) with 31 male and 5 female patients. Time between SBRT and transplant varied with an average of 227 days, range 6-612 days. Post-treatment imaging showed that 36 lesions (65%) had at least partial response with 19 lesions (35%) showing no response or progressive disease at time of transplant. When looking at explant pathology, 46 lesions had at least a partial response while 10 had no response. There was a complete pathologic and radiologic response in 11 lesions and nine areas exhibited both partial radiologic and pathologic responses. Treated areas with progressive disease on imaging had the largest average PTV at 66.83 cm3. There was an overall average change in AFP from prior to treatment to before transplant of -29.66% with no significant changes between pathologic and radiologic response groups. There was a significant correlation between time to transplant and pathologic response with areas showing complete response having longer average time (249 ± 132 days) vs partial and no response (F (2,35) = 3.465, p=0.026).

Conclusion: The most significant correlation with radiographic and pathologic complete response was a longer time interval from SBRT, with an optimal time of 35 weeks. Though statistically insignificant, patients with higher AFP prior to transplant and prior to SBRT treatments correlated with complete pathologic response vs partial or no response. Further work will investigate how MRI based treatments affect pathologic and radiologic response as well as predictors of response.