ESTRO 38 Abstract book

S465 ESTRO 38

Conclusion SBRT to oligometastatic bone metastases did not improve QOL or pain response compared to conventional radiotherapy. Only patients with an interval between primary tumor and oligometastatic disease >12 months showed prolonged OS and PFS after treatment with SBRT. PO-0882 Outcome and Toxicity of Hypofractionated Image-Guided SABR for Spinal Oligometastases C. Billiet 1 , C. Mercier 1,2 , F. Vandaele 1 , P. Vermeulen 3 , S. Van Laere 3 , P. Huget 1 , D. Verellen 1 , P. Dirix 1 1 I Department of Radiation Oncology, Iridium Kankernetwerk, University of Antwerp, Belgium; 2 University of Antwerp, Molecular Imaging- Pathology- Radiotherapy & Oncology MIPRO, Antwerp, Belgium ; 3 Oncologisch Centrum GZA, Translation Cancer Research Unit, Antwerp, Belgium Purpose or Objective To evaluate tumor control and toxicity after high-dose stereotactic hypofractionated intensity modulated radiation therapy for patients with spinal oligometastases. Material and Methods Between Match 2015 and March 2018, 40 consecutive patients with a localized spine metastasis (C1 to sacrum) from a histologically confirmed solid tumor received stereotactic ablative radiotherapy (SABR) to a total of 44 lesions and were followed for at least 6 months. SABR was delivered in three fractions of 8-10 Gy following international consensus delineation guidelines. All patients were treated with linac-based rotational SABR using cone-beam CT image-guidance and online correction of set-up errors in six degrees of freedom. An optical surface monitoring system (OSMS) was used to ensure patient immobilization. Factors associated with progression-free survival were retrospectively investigated by multivariate analysis. Local recurrence was defined as regrowth within the irradiated field or clear exacerbation of symptoms such as pain and motor deficits. Table 1 : Patient and tumor characteristics

Results Mean follow up was 69 months for all patients. Patient and tumor characteristics are depicted in Table 1. The 1-year progression free survival (PFS) was 97% for all patients (median PFS 92 months)(Figure 1) . In three patients (6,8%) a local recurrence was observed. No radiation- induced myelopathy was observed. Vertebral compression fractures developed de novo in 4.5% (2/44) of patients. In multivariate analysis, synchronous (vs. metachronous) lesions (p< 0.001; HR= 113.5), older age (p= 0.01; HR= 1.1) and no systemic therapy (p= 0.02; HR= 8.1), were correlated with worse PFS. In subgroup analysis for prostate cancer patients only, synchronous lesions were confirmed as significant predictive factor for PFS in multivariate analysis. The mean volume of the gross target volume (GTV) was 11 cc and for the clinical target volume (CTV) 32cc. Mean dosimetric parameters D2%, D50% and D98% for the CTV and planning target volume (PTV) were 32.0 Gy, 18.6 Gy, 29.0 Gy and 33.1 Gy, 21.7 Gy, 30.7 Gy respectively. Figure 1 : Progression free survival for all patients

Conclusion These results show high rates of efficacy and minimal toxicity in patients treated with high-dose stereotactic hypofractionated RT for spinal metastases. Oligometastatic patients with metachronous lesions, younger age and additional systemic therapy seem to