ESTRO 36 Abstract Book

S736 ESTRO 36 2017 _______________________________________________________________________________________________

schemes. With the use of SBRT there is also a need for accurate target delineation. The hypothesis is that MRI allows for better visualization of the extend of bone metastases in mRCC for contouring in the context of stereotactic treatment planning. Material and Methods From 2013 to 2016, nine consecutive patients who underwent SBRT for RCC bone metastases at our center were included. A planning CT and MRI were performed in radiotherapy position according to our clinical protocol. CT images were performed at 1 mm slice thickness on a large bore CT scanner (Philips, The Netherlands). In addition, all patients underwent a 1.5 Tesla MRI scan (Philips Ingenia, The Netherlands) at 1.1 – 4 mm slice thickness. For every patient, T1-weighted images were acquired in transversal and sagittal direction, including a transversal mDIXON scan, as well as T2-weighted images in transversal and sagittal direction, and diffusion weighted images (DWI) according to our clinical MRI protocol. Gross tumor volumes (GTV) in both CT and MRI were delineated. Contouring was performed by a specialized radiation oncologist, based on local consensus contouring guidelines (T1 images were used for target delineation aided by the information derived from the T2 and DWI sequences). In both CT and MRI the GTV volumes, conformity index (CI) and distance between the centers of mass (dCOM) were compared. Statistical differences in volumes between CT and MRI were tested with Wilcoxon rank sum test. Results Nine patients with 11 RCC bone metastases were evaluated. The volumes of the lesions on MRI were larger compared to the CT, for all but one lesion (Table 1). This lesion was comparable in size on MRI and CT. Two visual examples of the difference in delineation are shown in Figure 1. The median GTV volume on MRI was 33.39mL (range 0.2mL – 247.6mL), compared to 14.87mL on CT (range 0.2mL – 179.4mL). The difference in volume as delineated on CT and MRI was statistically significant (p=0.005). The CI in the different lesions varied between 0.08 and 0.75. The dCOM varied between 0.78 and 13.34 mm.

Conclusion Contouring of RCC bone metastases on MRI resulted in both clinically and statistically significant larger lesions compared with CT. MRI seems to represent the extend of the GTV in RCC bone metastases more accurately, possibly due to improved visualization of bone marrow infiltration. Contouring based on CT-only could result in an underestimation of the actual tumor volume, which may cause an under dosage of the GTV in SBRT treatment plans. EP-1391 Digestive toxicity after conformal radiotherapy for palliative cervico-thoracic spinal metastases G. Peyraga 1 , D. Caron 1 , Y. Metayer 2 , Y. Pointreau 3 , F. Denis 3 , G. Ganem 3 , C. Lafond 3 , S. Roche 3 , O. Dupuis 3 1 Institut de Cancérologie de l'Ouest, Radiation Therapy, Angers, France 2 Centre Jean Bernard, Medical Physics, Le Mans, France 3 Centre Jean Bernard, Radiation Therapy, Le Mans, France Purpose or Objective The palliative treatment of cervico-thoracic spinal metastases is based on a conformal radiotherapy (CRT), delivering 30 Gy in 10 fractions (5 days a week for 2 weeks). Digestive toxicities (esophagitis, nausea and vomiting) are common after these radiations and cause a clinical impact probably underestimated in patients. We performed a retrospective monocentric study of early digestive toxicities occurred secondarily to palliative CRT of cervico-thoracic spinal metastases. Material and Methods All patients receiving palliative CRT at Jean Bernard Center from January 2013 to December 2014 of spinal metastases (all primitive tumors were included) between the fifth cervical vertebra (C5) and 10th thoracic vertebra (T10) for which clinical follow-up was available beyond 3 months were included. Re-irradiations were excluded. CRT was delivered by a linear accelerator (CLINAC, Varian). Premedication to prevent digestive toxicities was not recommended. Adverse events (esophagitis and nausea/vomiting < 3 months) were evaluated according the NCI-CTCae (version 4). Results From January 2013 to December 2014, 128 patients met the study criteria. The median age was 69.6 years [31.8; 88.6]. The majority (84.4%) patients received a dose of 30 Gy in 10 fractions. The median treatment duration was 13 days [3-33]. Forty patients (31.3%) experienced grade 2 or 3 of esophagitis (35 grade 2 (27.4%) and 5 grade 3 (3.9%)), and 8 patients (6.3%) experienced grade 2 or 3 of nausea or vomiting (6 grade 2 (4.7%), 1 grade 3 (0.8%) and 1 grade 4 (0.8%)). The risk of digestive toxicities seems to be related to spinal localization of metastases (38.5% of grade 2 or 3 esophagitis if radiation from C5 to T4 versus 31.2% if radiation from T5 to T10, and 87.5% of nausea and vomiting concerned T9 or T10) and to the number of