ESTRO 38 Abstract book

S108 ESTRO 38

Purpose or Objective SBRT with fiducial tracking is a safe and effective treatment for medically inoperable early stage non-small cell lung cancer (ES-NSCLC). Bronchoscopy affords an all- in-one evaluation of mediastinal lymph nodes, visualization of the central airway, biopsy of the primary tumor, and placement of fiducials for tracking. Tumor proximity to the central airway is a known risk factor for toxicity. In this report, we examine the clinical outcomes of a diverse cohort of patients with both central and peripheral tumors treated with 5 fraction SBRT using fiducial tracking. We identify endobronchial involvement as a predictor of poor clinical outcome and treatment- related death. Material and Methods Medically inoperable patients were treated with frameless robotic SBRT per institutional protocol. Majority (41) underwent bronchoscopy with placement of 3 to 5 fiducials with the remainder placed under CT guidance. Clinical examination and PET/CT imaging were completed for staging and at 6 month follow up intervals. Follow-up was performed using a combination of clinical evaluation and PET/CT scans. Patients were stratified based on clinical stage, tumor location (central versus peripheral) and endobronchial involvement. Results From December 2010 to December 2015, 50 patients with biopsy proven ES-NSCLC (stage I - 31; stage II – 19) deemed medically inoperable with median age of 75 were treated with fiducial-based SBRT to 50 Gy in 5 fractions. Twelve central and 38 peripheral tumors were treated with a median tumor diameter of 3.4 cm (range, 1.1 to 7.3 cm) and staged as T1 (n=18), T2 (n=22), and T3 (n=10) per the AJCC 7 th edition. At median follow up of 36 months, overall survival (OS) was 52%. Survival did not differ between peripheral and central tumors (53% vs 50%; p=0.47) nor between stage I and stage II disease (51% vs 52%; p=0.674). Local control (LC), regional control (RC), distant metastasis free survival (DMFS), and disease free survival (DFS) were 88%, 89%, 83% and 73%, respectively. Of 41 patients who underwent bronchoscopy for fiducial placement, five tumors, all of which were centrally located, were found to have gross endobronchial involvement. LC and OS for this cohort was 66% and 20%. Cox regression analysis identified endobronchial involvement as a predictor of OS while controlling for age, location, and stage (OR: 4.096, p-value =0.046). Endobronchial involvement was also an independent predictor for grade 5 pulmonary toxicity (n=4, p=0.007). Specifically, 3 patients with gross endobronchial disease went on to experience grade 5 bronchial stricture. Conclusion Central location of ES-NSCLC is known to predict for SBRT- related toxicity. Here we report endobronchial involvement observed during staging bronchoscopy as a significant predictor of poor overall survival and Grade 5 pulmonary toxicity. The poor prognosis and high rates of treatment-related toxicity in patients with central ES- NSCLC may be due in part to gross tumor endobronchial involvement. PV-0207 Is V37Gy a Better Dose Predictor for Radiation Pneumonitis for Lung Proton Therapy? W. Harris 1 , S. O'Reilly 1 , V. Jain 1 , B.K. Teo 1 , L. Dong 1 , S. Feigenberg 1 , A. Berman 1 , W. Zou 1 1 University of Pennsylvania, Radiation Oncology, Philadelphia, USA Purpose or Objective Radiation pneumonitis (RP) is one of the most common forms of toxicity that affect lung cancer patients. About 15-20% of locally-advanced non-small cell lung cancer (LA- NSCLC) patients treated with chemoradiotherapy (CRT) develop RP. The dosimetric parameters used clinically to reduce the likelihood of RP have traditionally been V20Gy

1 Liverpool Hospital, Cancer Therapy Centre, Liverpool, Australia; 2 Prince of Wales Hospital, Department of Radiology, Randwick, Australia; 3 Liverpool Hospital, Ingham Institute of Applied Medical Research, Liverpool, Australia Purpose or Objective There has been growing interest in use of MRI in lung cancer radiotherapy. This study aims to evaluate the changes seen in lung cancer volume and position on MRI during a course of radiotherapy, and compare this with the current standard of practice, serial cone-beam CT (CBCT). Material and Methods Patients with histologically or cytologically confirmed lung cancer receiving more than 12 fractions of radiotherapy, either alone or with concurrent chemotherapy, were enrolled in a prospective study of serial CBCT and MRI in during-treatment (Day 1, Day 11, & Day 21) scans. Time- matched CBCT and MRI primary gross tumour volumes (GTVp) were manually delineated by a single observer on MIM software. Derived parameters (volume, & centre of mass (COM)) were analysed descriptively and using Bland- Altman plots and linear regression. Results 20 patients with 23 GTVp were eligible for inclusion. 60 CBCT/MRI scan pairs were analysed. Mean (± standard deviation) CBCT vs MRI volume change compared to baseline (Day 1) were 81% (±17) vs 80% (±29), and 70% (±31) vs 72% (±46) for Day 11 and Day 21 respectively. CBCT contours were on average 23% larger than paired MRI contours. MRI vs CBCT demonstrated a systematic bias of -0.92 mL, with absolute volume of CBCT being greater than MRI. Bland-Altman analysis demonstrated CBCT and MRI were not equivalent imaging modalities. No significant regression was found in during-treatment CBCT or MRI (p=0.65). No significant difference in slope of tumour regression was found between CBCT and MRI. A significant (> 0.5 cm) COM shift was observed from Day 1 to Day 21, at 0.54 (±0.42) vs 0.66 (±0.41) cm for CBCT vs MRI respectively.

Conclusion Changes in lung cancer volume and position during radiotherapy are different on CBCT and MRI. Further investigation is warranted if MRI is to be used for adaptive radiotherapy in the future. PV-0206 Gross endobronchial disease: predictor of clinical outcomes for early stage NSCLC treated with SBRT N. Aghdam 1 , S. Kataria 1 , M. Pernia 2 , C. Hall 3 , T. O’Connor 3 , L.Campbell 1 , S. Suy 1 , S.P. Collins 1 , R. Krochmal 4 , E. Anderson 4 , J. Lischalk 1 , B.T. Collins 1 1 Georgetown University Hospital, Department of Radiation Medicine, Washington DC, USA ; 2 Metropolitan Hospital Center, Department of Internal Medicine, New York, USA ; 3 Cornell University, The college of arts and sciences, Ithaca, USA ; 4 Georgetown University Hospital, Division of Pulmonary and Critical Care Medicine, Washington DC, USA