ESTRO 37 Abstract book

EP-2380 Feasibility and efficacy of SIB-IMRT based on MRI-CT fusion in NSCLC patients with brain metastases W. Huang 1 , Y. Dong 2 1 Shandong Cancer Hospital, Radiation Oncology 6, Jinan, China 2 University of Jinan-Shandong Academy of Medical Sciences, School of Medicine and Life Sciences, Jinan, China Purpose or Objective To assess the feasibility and therapeutic effects of simultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT) based on the fusion imaging of magnetic resonance imaging (MRI) and computed tomography (CT) as a dose-intensive technique in patients with brain metastases (BM) of non-small cell Twenty-eight NSCLC patients with 1 to 7 brain metastases were enrolled in this retrospective study between November, 2011 and February, 2015. Twenty patients (71.4%) had 1-3 metastases (oligometastases), otherwise, more than 3 metastases were seen in only 8 patients (28.5%). GTV (Gross tumor volume) contouring was based on the fusion imaging of MRI-CT, WBRT was prescribed in 37.5 Gy/15 fractions with a simultaneous boost in the metastatic lesions of 52.5 Gy/15 fractions. Results The median overall survival (OS) and intracranial progression free survival (PFS) for all the patients were 21.0 months and 14.0 months, respectively. The 6-month and 1-year OS were 78.6% and 46.4% respectively, while the 6-month and 1-year PFS were 67.9% and 21.4% respectively. Until the end of the follow-up, 17 patients (60.7%) were alive. No evidence of intracranial progress or recurrence was found in 10 patients (35.7%) during the SIB-IMRT with the dose/fractionation based on the fusion imaging of MRI-CT is feasible and safe. It is beneficial to the NSCLC patients with BM and can reduce the overall costs of treatment. EP-2381 Evaluation of reduced PTV margins for IGRT and IMRT of esophageal cancer M. Michalet 1 , F. Castan 2 , O. Riou 1 , C. Lemanski 1 , C. Llacer-Moscardo 1 , O. Lauche 1 , D. Azria 1 , N. Aillières 1 , J. Prunaretty 1 1 CRLC Val d'Aurelle/Paul Lamarque, Radiothérapie, Montpellier Cedex 5, France 2 CRLC Val d'Aurelle/Paul Lamarque, Unité de biométrie, Montpellier Cedex 5, France Purpose or Objective To demonstrate the feasibility of reduced PTV margins of 5 mm for Intensity Modulated Radiotherapy (IMRT) in esophagus cancers using Image Guided Radiotherapy (IGRT). Material and Methods Patients who underwent IMRT in 2016 at the Institute of Cancer of Montpellier, for a primitive cervical or thoracic esophageal cancer, of any TNM stage and histology, were included. Reduced isotropic PTV margins of 5 mm were retrospectively studied. The IGRT was carried out daily, either with kV-kV or either with Cone Beam CT (CBCT). Image registration was done by radiation therapists. Tumor coverage with reduced PTV margins was retrospectively assessed by a physician on every CBCT registration. Differences between radiation therapist and physician registrations were checked. Results 30 patients treated between the 09/02/2015 and the 01/18/2017 were included. There were 18 squamous cell carcinomas (60%), 8 adenocarcinomas (27%) et 3 lung cancer (NSCLC). Material and Methods follow-up. Conclusion

neuroendocrine carcinomas (10%). The localization was thoracic esophagus in 93% of cases (10% the upper third, 33% the middle third, 30% the lower third, 20% the middle et lower third), and cervical in 7% of cases. 145 CBCT registrations were retrospectively assessed (2 to 5/ patient, maximum 1/week randomly determined). The tumor was covered by the PTV in 61% of the cases before CBCT and in 95% of cases after CBCT. The tumoral coverage was not obtained in 7 CBCT, corresponding to 5 different patients. The registration differences were less than 5 mm in 96% of the cases. The differences were greater for the lower third of the thoracic esophagus. Example of errors with only bone-based registration :

Variation between physician registration / radiation therapist (median and maximum values, in cm)

Registration of radiation therapist after CBCT (median and maximum values, in cm)

Longitudinal axis

0,31 (0,00 – 2,59)

0,07 (0,00-0,54)

Vertical axis 0,30 (0,00 – 3,06) Lateral axis 0,26 (0,00 – 2,10)

0,04 (0,00 – 0,75) 0,07 (0,00 – 0,78)

Conclusion IGRT improved the precision of IMRT delivery in esophageal cancers. A PTV margin of 5 mm seemed to be sufficient in most of the cases. A long term follow up is necessary. EP-2382 Impact on treatment plan of daily MV EPI versus MV CBCT imaging for prostate cancer IGRT A. Monteiro 1 , D. Rodrigues 1 , M.J. Fontes 1 , P. Varzim 1 , R. Figueira 1 , R. Lago 1 , S. Garcia 1 , T. Reis 1 , A.L. Carvalho 1 , G. Pinto 1 1 Hospital de São João, Serviço de Radioterapia, Porto, Portugal Purpose or Objective Radical radiotherapy for prostate cancer involves the administration of high doses of radiation therapy and should not be performed without a daily check image (IGRT). MV electronic portal images (EPI) or kV/MV conebeam CT (CBCT) are tipycally used as imaging modalities for prostate positioning. In the first case