ESTRO 36 Abstract Book

S168 ESTRO 36 _______________________________________________________________________________________________

Conclusion MRI-guided SBRT for pancreatic cancer with individually evaluated margins is technical feasible and safe, with no treatment related grade ≥3 toxicity. New strategies are applied, including an individual corset to reduce breathing motion, MRI based contouring and simulation of motion- integrated dose distributions. PV-0322 Rapid Early Response of Gastroesophageal Junction Tumors During Real-time MRI-Guided Radiotherapy H. Musunuru 1 , S. Rosenberg 1 , J. Bayouth 1 , K. Mitteur 1 , M. Ritter 1 , B. Paliwal 1 , M. Witek 1 , A. Baschnagel 1 , N. Uboha 2 , S. Lubner 2 , N. Loconte 2 , P. Harari 1 , M. Bassetti 1 1 University of Wisconsin Hospital and Clinics, Radiation Oncology, madison, USA 2 University of Wisconsin Hospital and Clinics, Medical Oncology, Madison, USA Purpose or Objective Multimodality comprehensive therapy has become the standard of care for locally advanced esophageal and gastroesophageal junction tumors. Tumor response to chemoradiation correlates with outcomes, however full response information generally awaits esophagectomy. Intra treatment predictors of response may allow improved personalization of therapy. Daily MRI allows direct quantification of GEJ tumor size. The aim of this study is to evaluate volumetric changes in gross tumor volume (GTV) for gastroesophageal junction (GEJ) cancer patients undergoing MRI-guided radiation therapy, as part of neoadjuvant chemoradiotherapy Material and Methods Five GEJ adenocarcinoma patients underwent MRI during simulation and with each treatment fraction immediately prior to radiation delivery. The GTV primary was contoured on MRI scans at fractions 5, 10, 15, 20 and 23 and compared to the baseline GTV (Fig 1). Change in GTV across time was expressed as percentage difference (between baseline and different fractions and between individual fractions) and in terms of absolute volume(cc). Results Median age and follow-up period for this cohort were 68 years and 46.5 days. The treatment regimen consisted of weekly carboplatin (AUC 2mg/ml/min) and paclitaxel (50mg/m 2 ) with concurrent radiotherapy, 50.4Gy in 28 fractions in three patients and 41.4Gy in 23 fractions in the remaining two patients. The earliest decrease in GTV (% change) was noted at fraction 10 when compared to baseline (Mean -52%, SD 4.6%; Fig 2A). Evaluation of percentage change in the GTV between different fractions (i.e. fraction 5 and fraction 10 etc.) also showed that the earliest change occurred between fractions 5-10 (Table 1). Mean (SD) of GTV at baseline and at fractions 5, 10, 15, 20 and 23 were 94.7cc(15.4), 93.9cc(14.8), 46.3cc(7.8), 39.7cc(6), 33.2cc(4.7) and 33.2cc(4.7), respectively.

Figure: Contouring with the aid of MRI and CT. Red: GTV. Green: pancreatic head. Blue: duodenum.