ESTRO 38 Abstract book

S758 ESTRO 38

fiducial markers, namely Visicoil to the liver and Disposable Gold Marker (Olympus Co. Tokyo, Japan) to the lung, on 1-2 weeks before CT. Patients planned as treated under free-breathing were taken CT with exhalation breath, and breath-hold were taken with inhalation breath. TrueBeam STX was used as the treatment device, and irradiation method was fixed multiple irradiation. Prescribed dose was 55.0 Gy/ 4 fr (n=8) or 66.0 Gy/ 10 fr (n=1), and all of them were D95 prescription, planned with RayStation. Average PTV volume treated was 33.9cc (range, 9.82-115cc). Conformity index in each irradiation field was 0.82-0.9, and the mean value was 0.86. Results Follow-up period was 2.3-8.8 months (median 5.1). As acute adverse event, radiation pneumonitis of grade 2 was observed in 1 patient in lung tumor patients. No serious adverse events related to radiotherapy and inserting fiducial markers were observed during the period. Local recurrence was observed in 1 patient, and distant metastasis was observed in 1 patient. Although treatment on free breathing was the basis, it was possible to shorten patient radiation exposure and treatment time by using in combination with respiratory arrest system. In the liver, to follow fiducial markers was difficult on the perspective direction, there were cases where a change was necessary in treatment plan. Conclusion SBRT using the SyncTraX FX4 system and fiducial markers was suggested as a safe and less burdensome treatment. EP-1392 Preoperative image-guided identification of response to nCRT in esophageal cancer (PRIDE study) A. Borggreve 1 , I. Defize 1 , G. Meijer 1 , H. Van Laarhoven 2 , H. Langendijk 3 , V. Mul 3 , F. Voncken 4 , M. Verheij 4 , P.S.G. University Medical Center Utrecht 1 , P.S.G. The Netherlands Cancer Institute 4 , P.S.G. University Medical Center Groningen 3 , P.S.G. Amsterdam University Medical Centers 5 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands ; 2 Amsterdam University Medical Centers, Department of Medical Oncology, Amsterdam, The Netherlands ; 3 University Medical Center Groningen, Radiation Oncology, Groningen, The Netherlands ; 4 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands ; 5 Amsterdam University Medical Centers, Cancer Center Amsterdam, Amsterdam, The Netherlands Purpose or Objective Nearly one third of patients undergoing neoadjuvant chemoradiotherapy (nCRT) for locally advanced esophageal cancer have a pathologic complete response (pCR) of the primary tumor upon histopathological evaluation of the resection specimen. The primary aim of this study is to develop a model that predicts the probability of pCR to nCRT in esophageal cancer, based on diffusion-weighted magnetic resonance imaging (DW-MRI), dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), 18 F-fluorodeoxyglucose positron emission tomography and computed tomography ( 18 F-FDG PET-CT). Accurate response prediction could lead to a patient- tailored approach with omission of surgery in the future in case of predicted pCR or additional neoadjuvant treatment in case of non-pCR. Material and Methods The PRIDE study is a prospective, single arm, observational multicenter study that will develop a multimodal prediction model for histopathological response to nCRT for esophageal cancer. A total of 200 patients with locally Electronic Poster: Clinical track: Upper GI (oesophagus, stomach, pancreas, liver)

Heart dose was associated with OS for advanced NSCLC treated by VMAT. EP-1391 Stereotactic body radiotherapy using a new real-time tumor tracking system and fiducial markers Y. Hiroshima 1,2,3 , K. Nitta 1 , T. Saitoh 1 , T. Ohno 4 , K. Shinoda 1 , Y. Tamaki 1,5 1 Ibaraki Prefectural Central Hospital, Radiation Oncology, Kasama, Japan ; 2 University of Tsukuba, Radiation Oncology- Faculty of Medicine, Tsukuba, Japan ; 3 University of Tsukuba Hospital, Radiation Oncology, Tsukuba, Japan ; 4 Dokkyo Medical University- Koshigaya Hospital, Radiology, Koshigaya, Japan ; 5 University of Tsukuba Hospital, Ibaraki Clinical Education and Training Center, Tsukuba, Japan Purpose or Objective A new fluoroscopic real-time tumor tracking radiotherapy (RTRT) system; the SyncTraX FX4 (Shimadzu Co., Kyoto, Japan) enables that transmits an irradiation permission signal to a treatment device while a fiducial marker is within a planned position and stops transmission when it comes off (Fig 1). In addition, while a system works, it can record a fiducial marker position quantitatively (Fig 2). Using this system, we can reduce the irradiation volume of normal tissue while guaranteeing the positional accuracy of the tumor even under free breathing and improve the patients’ burden and adverse events. We report the safety and the feasibility of the stereotactic body radiotherapy (SBRT) using this system.

Material and Methods Between October 2017 and June 2018, a total of 8 patients and 9 sites treated by SBRT with this system were retrospectively reviewed. This study included 7 men and 1 woman, whose age ranged from 66 to 86 (median 75). Treated sites of organ were lung (n=6) and liver (n=3). All of lung tumors were primary tumors and liver tumors were metastatic tumors. All patients were inserted several