ESTRO 36 Abstract Book

S172 ESTRO 36 2017 _______________________________________________________________________________________________

S.Y. Wu 1 1 Taipei Medical University Hospital, No.111- Section 3 Department of Radiation Oncology, Taipei, Chinese Taipei Purpose or Objective For locoregionally recurrent head and neck squamous cell carcinoma (HNSCC), appropriate therapeutic decisions and prognostic factors remain unclear. Material and Methods The enrolled 4,839 patients were categorized into four groups: Group 1 comprised those undergoing chemotherapy (CT) alone; Group 2 comprised those receiving reirradiation (re-RT) alone (total radiation dose ≥ 60 Gy through intensity modulation radiation therapy [IMRT]); Group 3 comprised those receiving concurrent chemoradiotherapy (CCRT) alone (irradiation total dose ≥60 Gy through IMRT); and Group 4 comprised those receiving salvage surgery with or without RT or CT. Results Age ≥ 65 years, Charlson comorbidity index (CCI) score > 6, clinical stage III-IV at first diagnosis, and recurrence- free interval < 1 year were significant independent prognostic risk factors for overall survival as per univariate and multivariate Cox regression analyses. After adjusting, adjusted hazard ratios (aHRs; 95% confidence intervals [CIs]) for overall mortality in recurrent clinical stages I and II were 0.63 (0.45–0.89, p = 0.009), 0.65 (0.52–0.83, p < 0.001), and 0.32 (0.26–0.40, p < 0.001) in Groups 2, 3, and 4, respectively, whereas they were 1.23 (0.99–1.52, p = 0.062), 0.69 (0.60–0.79, p < 0.001), and 0.39 (0.34–0.44, p < 0.001) for Groups 2, 3, and 4, respectively, for overall mortality in recurrent clinical stage III and IV. Conclusion Salvage surgery is the recommended first treatment choice for recurrent oral cavity and pharyngeal cancers. Re-RT alone and CCRT are more suitable for inoperable recurrent stage I-II oral and nonoral cavity recurrent HNSCCs, respectively. OC-0331 Cetuximab versus Platinum-based Chemoradiation in Locally Advanced p16 Positive Oropharyngeal Cancer C. Barney 1 , S. Walston 1 , P. Zamora 1 , N. Nolan 1 , V. Diavolitsis 1 , D. Blakaj 1 , J. Wobb 1 , D. Mitchell 1 , J. Grecula 1 , P. Savvides 2 , A. Bhatt 1 1 The Ohio State University, Radiation Oncology, Columbus- Ohio, USA 2 The University of Arizona Cancer Center at Dignity Health St. Joseph's Hospital, Medical Oncology, Phoenix, USA Purpose or Objective Randomized trials evaluating intensity modulated radiation therapy (IMRT) concurrent with platinum-based chemotherapy (PBC) versus cetuximab (C225) in treating oropharyngeal cancer (OPC) are underway but have yet to report preliminary data. Meanwhile, as a would-be step toward morbidity reduction, the off-trial use of C225 in p16+ patients is increasing in frequency, even in those who could potentially tolerate PBC. The purpose of this study was to retrospectively compare the efficacy of PBC versus C225 concurrent with IMRT in the treatment of locally From 2010 to 2014, 219 patients with stage III-IVB p16+ OPC were treated definitively (n=188, 6996-7000 cGy) or postoperatively (n=31, ≥6600 cGy) with IMRT plus concurrent PBC (n=155, Cisplatin-136 and Carboplatin-19) or weekly C225 (n=64). Log-rank/Kaplan-Meier analysis and Cox Regression modeling were used for univariate and multivariate analysis (MVA) respectively. Results Tumor and patient characteristics were well balanced – PBC patients had increased median follow-up time and advanced p16+ OPC. Material and Methods

point with maximal surface distance (MSD). A validated deformable image registration (DIR) propagated the POs from recurrence-CT to planning-CT. The distance from POs to the surface of the GTV was calculated and presented as mean distance from all four POs to the GTV. The patient specific GTV-CTV1 margin was calculated as median surface distance from GTV to CTV1. Difference between LRR distribution in groups with small and large CTV margins was evaluated using Kolmogorov-Smirnov test (p<0.05). Results In total 1,581 patients were identified and 297 had LRR within the first 3 years of follow-up; of those, 172 patients had CT-verified recurrent disease. Among them, 50% had GTV-CTV1 margin less than 5 mm and 50% larger than 5 mm. There was no difference in sex, tumour site, stage, tumour differentiation and p16-status between these two groups. After successful DIR, in total 192 recurrences were further analysed in the two margin groups; no significant difference in LRR distribution was found (p=0.6). Of the POs in the first and the second groups, 58% and 64% received 95% of the prescription dose, respectively (Figure 1).

Conclusion The presented data do not suggest any difference in distribution of loco-regional recurrences in relation to CTV margins. Such a difference could be expected if the CTV margin was a key component for loco-regional recurrence probability. OC-0330 Locoregionally Recurrent Head and Neck Squamous Cell Carcinoma