2056 - Impact of Complete GTV Inclusion within =110% Isodose on Local Control and Toxicity after Spine Reirradiation SBRT
Presenter(s)
A. N. Elguindy1,2, E. R. Cochran1, K. Dibs1, K. Fernando1, M. Addington1, E. Yap1, R. S. Handschuh1, D. J. DiCostanzo1, D. Schneider3, B. Park3, J. B. Elder3, R. R. Lonser3, D. Boulter4, E. Bourekas4, D. J. Konieczkowski1, S. Beyer1, S. Zhu1, R. Singh1,5, R. Raval1, J. C. Grecula1, 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, El-Demerdash Hospitals, Ain Shams university, Cairo, Egypt, 3Department of neurosurgery, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH, 4Department of Neuroradiology, The Ohio State University Wexner Medical Center, Columbus, OH, 5Eugene M. & Christine E. Lynn Cancer Institute, Baptist Health, Boca Raton, FL
Purpose/Objective(s):
Spine reirradiation with stereotactic body radiation therapy (reSBRT) is increasingly utilized for local progression. Dose escalation of complete gross tumor volume (GTV) within =110% isodose cloud (GTV boost) may enhance local control, but toxicity remains unclear. We evaluated outcomes associated with GTV boosting in this spine reSBRT cohort.Materials/Methods:
We retrospectively analyzed 61 lesions (55 patients) treated with reSBRT for local progression following initial SBRT. Follow-up was assessed by reverse Kaplan–Meier method, overall survival (OS) was estimated using the Kaplan–Meier method, and cumulative incidence of local progression was estimated where death was a competing event.Results:
Median age was 65 years (IQR: 56, 70), 69% were females, and 89% had KPS =80%. The most common primary sites were lung (25%), renal cell carcinoma (18%), and gastrointestinal cancers (15%). Forty lesions (65 %) were cervicothoracic and 21 (35 %) were lumbosacral. Based on Spinal Instability Neoplastic Score (SINS) at initial SBRT, 33 lesions (54 %) were stable (=6) and 27 (44 %) as indeterminate (7-12). Median interval between SBRT courses was 11 months. The most common first and second SBRT regimens were 27 Gy in 3 fractions (75% and 65%, respectively), with median cumulative EQD2 of 85.5 Gy. GTV boost was delivered in 52% of lesions. OS follow up time was 43.7 months (95% CI: 32.2, –). Median OS after reSBRT was 10.9 months (95% CI: 9.4, 16.2), with 12- and 24-month OS of 47% and 29%, respectively. Median LPFS was 10.6 months (95% CI: 6.3, 16.0). At 12 months, LPFS was 49% with GTV boost versus 45% without boost; at 24 months, 33% versus 19%, respectively. Boosted lesions had greater median LPFS (11.2 vs. 8.0 months, p = 0.12). 1-year cumulative incidence of local progression was 10% (95% CI: 4%, 19%) and of death was 43% (95% CI: 30%, 56%). Six lesions (10%) experienced progression after reSBRT (3 with stable SINS, and 3 with indeterminate), five of which (83%) occurred in non-boosted patients. Lesions with boosted RT had lower cumulative incidence of local progression at 12 months (3% vs 17%, p = 0.1). Overall, vertebral compression fracture (VCF) occurred in 12% (2 with initial stable SINS and 3 with indeterminate SINS) and radiation myelopathy in 10.5%. Myelopathy was more likely in GTV boosted patients (11% vs 4.8%, p = 0.6) and VCF was similar regardless of boosting (11% vs 11%, p > 0.9).Conclusion: GTV inclusion within =110% Isodose during spine reSBRT was associated with improved LC. VCF rates were similar across GTV boosting status. Myelopathy was uncommon but occurred more often with GTV boosting. These findings support the feasibility of hotspot-based GTV dose escalation in patients undergoing reSBRT. Larger studies are warranted to clarify the magnitude of LC benefit and toxicity.