2439 - Early PET Metabolic Response Predicts Local Control following Spine Stereotactic Body Radiotherapy
Presenter(s)
K. Dibs1, G. Tocaj2, E. R. Cochran1, A. N. Elguindy1, R. Raval1, S. Zhu3, J. C. Grecula1, A. Tocaj4, E. M. Thomas5, R. Singh1, F. Fekrmandi6, S. Beyer1, E. Bourekas7, D. Boulter7, J. B. Elder8, D. Schnieder4, B. Park9, A. Chakravarti1, J. D. Palmer1, and D. M. Blakaj1; 1Department of Radiation Oncology, James Cancer Hospital/Wexner Medical Center, The Ohio State University, Columbus, OH, 2Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, OH, 3University of Florida, Gainesville, FL, 4The Ohio State University, Columbus, OH, 5The Renaissance Institute of Precision Oncology & Radiosurgery, Winter Park, FL, 6Department of Radiation Medicine, Roswell Park Comprehensive Cancer Center, Buffalo, NY, 7Department of Neuroradiology, The Ohio State University Wexner Medical Center, Columbus, OH, 8Ohio State University, Columbus, OH, 9Department of neurosurgery, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH
Purpose/Objective(s): Early identification of local failure after spine stereotactic body radiotherapy (SBRT) remains challenging using conventional imaging alone. Positron emission tomography (PET) may provide an earlier biomarker of treatment response through metabolic assessment. We evaluated whether early changes in maximum standardized uptake value (SUVmax) following SBRT are associated with subsequent MRI-defined local control (LC).
Materials/Methods: We retrospectively analyzed 61 spinal metastases treated with SBRT with available pre- and post-treatment PET imaging. SUVmax was recorded at baseline and at first post-SBRT PET. Relative SUV change was calculated as proportional reduction from baseline. Early PET was defined as imaging within 0–3 months after SBRT, with subgroup analyses at 3–6 months and >6 months. Lesions were stratified by SUV reduction threshold (>35% vs =35%). Local control was assessed by MRI. Kaplan–Meier methods estimated LC, and differences were compared using the log-rank test. Continuous variables were analyzed using the Wilcoxon rank-sum test and categorical variables with Fisher’s exact test. A two-sided p-value <0.05 was considered statistically significant.
Results: Median age was 65 years (range 18–83), and 66% of patients were male. Common primaries included lung (23%), sarcoma (18%), and gastrointestinal malignancies (16%). Fifty-five percent had bone-only disease. Most lesions received 27 Gy in 3 fractions (59%). Median PTV was 50.1 cc, and 69% received a GTV boost. Median baseline SUVmax was 11.3, decreasing to 3.8 post- SBRT, corresponding to a median relative reduction of 60%. Baseline demographic, disease, and treatment characteristics did not differ between LC and progression groups (all p>0.05). However, post-SBRT SUVmax was significantly higher in lesions with disease progression compared with LC (10.35 vs 2.80, p<0.001), and relative SUV reduction was significantly smaller (37% vs 63%, p=0.023). Among patients undergoing early PET (0–3 months), =35% SUV reduction was associated with significantly inferior LC compared with >35% reduction (p=0.0067). Similar patterns were observed at later PET intervals, with progressive lesions demonstrating smaller metabolic responses and shorter time to MRI-confirmed progression.
Conclusion: Early metabolic response on PET following spine SBRT is strongly associated with subsequent local control. A >35% SUV reduction within 3 months identifies lesions with improved LC, whereas limited metabolic response predicts higher risk of progression. Early PET may serve as a noninvasive biomarker to refine post-SBRT surveillance.