Results All HRFs were significantly associated with LR (p<0.01)

1. High-risk CT features for detection of local recurrence after stereotactic ablative radiotherapy for lung cancer Suggested F/U algorithm for patients eligible for salvage therapy Requires validation in other datasets, preferably with PET-CT available. Kitty Huang, MSc, MDCM1, SashendraSenthi, MBChB, FRANZCR,2, David A. Palma, MD, MSc, PhD1 , Femke O. B. Spoelstra, MD, PhD2, Andrew Warner, MSc1, Ben J Slotman, MD, PhD2, Suresh Senan, MRCP, FRCR, PhD2 1.Department of Radiation Oncology, London Regional Cancer Program, London, ON, Canada. 2.Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands • Conclusion: • Systematic assessment for HRFs on CT imaging enables accurate prediction of local recurrence • This may reduce unnecessary biopsy and ensure the earlier use of salvage therapies • Reference: Huang et al. Radiotherapy & Oncology, 2013 Suggested F/U algorithm for patients eligible for salvage therapy Requires validation in other datasets, preferably with PET-CT available • Background: • SABR is a guideline recommended treatment for medically inoperable early stage NSCLC. • Local recurrence is rare (~10%), however fibrosis is very common (~90%), confounding timely diagnosis and salvage treatment. • Objective: • We performed a blinded assessment of CT imaging high-risk features (HRFs) in patients with and without local recurrences. • Materials and Methods: • Pathologyproven recurrences (n=12) matched 1:2 to non-recurrences (n=24) based on baseline factors • 3 ROs, blinded to outcomes, scored serial CT images projected onto a large screen for HRFs • Results • All HRFs were significantly associated with LR (p<0.01) • One new HRF was identified: cranio-caudal growth (p<0.001) • The best individual predictor of LR was opacity enlargement after 12-mos (100% sensitivity, 83% specificity, p<0.001) • The odds of LR increased 4-fold for each additional HRF detected • ≥3 HRFs was highly sensitive and specific for LR (both >90%) *HRFs: Enlarging opacity, cranio-caudal growth, sequential enlargement, enlarging opacity after 12 months, loss of linear margins, bulging margin and loss of air bronchograms. **Rule out nodal or distant recurrence prior to salvage *HRFs: Enlarging opacity, cranio-caudal growth, sequential enlargement, enlarging opacity after 12 months, loss of linear margins, bulging margin and loss of air bronchograms. **Rule out nodal or distant recurrence prior to salvage