Abstract book - ESTRO meets Asia

S86 ESTRO meets Asia 2018

overall survival for these patients. However, for non- surgery tumors, the use of radiotherapy should be considered. PO-212 Assessing tumour centrality in lung SABR: effects of variations in contouring the bronchial tree. W. Ghandourh 1,2 , J. Dowling 3 , V. Batumalai 1,4 , S. Jacob 5 , A. Oar 6 , L. Holloway 1,2,4 1 University of New South Wales, Medicine, Sydney, Australia 2 Ingham Institute of Applied Medical Research, Medical Physics, Sydney, Australia 3 Commonwealth Scientific and Industrial Research Organi sation CSIRO- Australia, Computer Sciences, Herston, Australia 4 Liverpool and Macarthur Cancer Therapy Centres- Sydne y- New South Wales- Australia, Radiation Therapy, Sydney, Australia 5 Ingham Institute of Applied Medical Research, Collaboration for Cancer Outcomes Research and Evaluat ion CCORE- Sydney- Australia, Sydney, Australia 6 Liverpool and Macarthur Cancer Therapy Centres- Sydne y- New South Wales- Australia, Radiation Oncology, Sydney, Australia Purpose or Objective Stereotactic Ablative Body Radiotherapy (SABR) has emerged as the standard of care for patients with inoperable, early-stage lung cancer. However, due to the increased risk of toxicity, central lesions (within 2cm from the proximal bronchial tree PBT) are commonly excluded from this treatment option. This study aimed to assess the inter-observer variability in manual contouring of the PBT and its effect on the clinical assessment of tumour centrality. Material and Methods CT scans of 41 patients (43 tumours), previously treated with SABR at a single institute, were identified. Each patient’s contour of the PBT, created at the time of their treatment, was compared against new subsequent contours that are generated by a radiation therapist then verified by a radiation oncologist. Initial and subsequent contours of the PBT were compared in terms of volume, distance to the tumour, and other metrics including Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD). Results Mean volume of the initial PBT contours was 24.98ml (±7.47ml), compared to 49.32ml (±11.98ml) for the subsequent contours (p <0.001). Mean DSC and HD were 0.62 (±0.08) and 26.52mm (±6.76mm), respectively. The mean distance to tumour volume, measured from the initial and subsequent contours, were 3.72cm (±1.24cm) and 3.07cm (±1.23cm), respectively (p <0.001). Using the subsequent contours of the PBT, 7/43 tumours were considered central (≤2.0cm), compared to 3/43 when using the initial contours (Figure.1).

Conclusion Adoption of 4D-CT scanning and VMAT treatment delivery has enabled us to treat larger tumours, which seems to be particularly advantageous for large midline tumours. We hypothesise that radiotherapeutic advancements can increase the number of patients treatable to a radical radiotherapy dose without PTV compromise and further work is underway to confirm this and the possible impact it might have on our workload and resources. PO-211 Adjuvant radiotherapy may not improve the survival for patients < 45 years old with thymic carcinoma J. Wen 1 , F. Min 1 , C. Jiayan 1 , L. Di 1 , X. Xinyan 1 1 Fudan University Shanghai Cancer Center, Department of Radiation Oncology, Shanghai, China Purpose or Objective To analyze the roles of postoperative radiotherapy (PORT) and surgical treatment for younger patients with thymic carcinoma (TC). Material and Methods Between 1988 and 2015, 136 younger patients diagnosed with TC were identified using the Surveillance, Epidemiology, and End Results (SEER) database. The analysis focused on overall survival (OS). Survival rates, univariate and multivariate analyses of prognostic factors were performed using the Kaplan–Meier method, the log rank test and Cox's proportional hazard method (backward step-down process based on Akaike information criterion (AIC)), respectively. Results The mean age of diagnosis was 37.0 ± 7.6. Among them, the majority was male (50.7%) with regional stage (40.4%). 39 patients underwent radical surgery, 39 received non- radical surgery and PORT was received by 38.2% of patients. Median OS was 43 months and 5-year survival rate was 39.6%. In the total cohort, multivariate Cox analysis showed that female (hazard ratio [HR] = 0.62, 95% CI 0.38-0.99, p=0.048), Pacific Coast region (HR = 0.44, 95% CI 0.26-0.75, p=0.003), radical resection (HR = 0.22, 95% CI 0.10-0.48, p<0.001) were associated with superior OS. Radiotherapy (HR = 0.70, 95% CI 0.43-1.15, p=0.159) showed a trend to improve survival. However, PORT was not an independent prognostic factor for those received surgery (p>0.05). Conversely, in the subgroup analysis, favorable impacts of radiotherapy were observed for those who didn’t received surgery (Median OS: yes vs. no, 30 months vs 15 months, p=0.024). Conclusion Our study shows the prognosis of younger TC patients is dismal. Radical surgical resection should be recommended for those with resectable disease. PORT may not improve

Conclusion Significant inter-observer variability was observed in manual contouring of the PBT; variations were most prevalent in the lower lobe branches and in determining