479 Background: Stereotactic body radiation therapy (SBRT) has found utility in oligometastatic liver lesions by providing excellent local control in most patients. These tumors are not routinely biopsied to evaluate for histologic grade due to high risk of seeding. Non-invasive pre-treatment radiographic findings may be able to identify a subset of patients at higher risk of local recurrence. Methods: Retrospective review of an IRB-approved database of liver metastases treated with SBRT yielded 55 patients for final analysis. Liver parenchyma and metastatic liver lesions were contoured using MIM version 6.6.5. Receiver Operating Characteristic curves and mean values were used to generate binary cutoffs for toxicities and Kaplan-Meier analysis, respectively. Computer Tomography features, like density, skew, kurtosis, variance, and volume, based on our pre-SBRT planning liver protocol images and their relationship with outcomes and toxicities were examined. Results: Largepre-SBRT density differences between oligometastatic lesions and liver parenchyma, as measured by Hounsfield Units, was associated with a 3.248 increased risk of local failures (p = 0.027) and grade 3 or higher late non-hepatobiliary toxicities (p = 0.032). There were no associations with overall survival. Lesions with large variance in density was associated with grade 3 or higher acute hepatobiliary toxicities (p = 0.043). Conclusions: Density metrics in metastatic liver lesions are readily available in most treatment planning systems and may be a prognostic indicator of tumor aggressiveness. Higher radiation doses may be needed to reduce rates of local recurrence in these patients. Further studies should examine if post-treatment density metrics are dose-dependent and correlate with outcomes.
Repeat stereotactic body radiation therapy (SBRT) for salvage of isolated local recurrence after definitive lung SBRT