ESTRO 2021 Abstract Book

S162

ESTRO 2021

radiation in normal tissues. However, this assumption may not be valid. Many VDAs have a narrow window of activity such that while they preferentially damage tumor vessels at specific doses, at higher doses normal vessels can also be damaged. Radiation itself can also induce vascular damage and if this happens in the surrounding normal tissues then any subsequent recovery could be severely impaired if AIs are administered. Limited data from our own group suggest that the systemic toxicity of certain VTAs may also be altered as a result of radiation induced inflammatory responses. Rather than simply assuming no effects of combining VTAs and radiation in normal tissues, one should perform studies in both tumors and normal tissues to clearly demonstrate a therapeutic benefit. In this presentation we will discuss the rationale for combining VTAs with radiation and summarize the results of this combination in tumors and, more importantly, in both early and late responding normal tissues. Supported by grants from the Danish Cancer Society and the Danish Council for Independent Research: Medical Sciences.

SP-0239 NOTCH interference and lung radiation response M. Vooijs The Netherlands

Abstract not available

SP-0240 DDR inhibition combined with thoracic irradiation side effects M. Hecht Germany

Abstract not available

Joint symposium: ESTRO-RANZCR - Challenges and benefits of SBRT

SP-0241 Primary and adjuvant pancreatic SBRT for close or positive margins A. Namysł-Kaletka 1 , J. Wydmanski 2 , I. Debosz-Suwinska 2 , R. Kulik 3 , A. Roch-Zniszczol 2 , D. Gabrys 2 1 Maria Sklodowska – Curie National Research Institute of Oncology Gliwice branch , Radiotherapy Department, Gliwice, Poland; 2 Maria Sklodowska – Curie National Research Institute of Oncology Gliwice branch , Radiotherapy Department, Gliwice, Poland; 3 Maria Sklodowska – Curie National Research Institute of Oncology Gliwice branch , Radiotherapy Planning Department, Gliwice, Poland Abstract Text The standard of care in pancreatic cancer is surgery which has been improved over the years. Unfortunately, the percentage of R1 resection is still high and can be as high as 50%. The status of the margins remains a predictor of relapse, but also of survival. Patients with a R1 surgery had a lower median survival rate compared with an R0. Moreover, around 80% of patients are inoperable at the diagnosis and at least a third of the patients die of complications related to local progression with or without any evidence of metastatic disease. SBRT seems to be a promising method for improving local control and outcomes without increasing the toxicity of the treatment, and shortening overall treatment time, but still there is no standard definition for close margins in the pancreatic adenocarcinoma. So far, there is also no clear consensus on the treatment volume for adjuvant stereotactic radiotherapy. Some studies have attempted to locate locoregional failure and answer the question whether the volume reduction will increase the risk of recurrence. Successful treatment of pancreatic cancer is difficult due to pancreatic tumor localization. The dose delivery is limited by the proximity of radiosensitive surrounding organs such as the duodenum, the jejunum and the stomach, and the uncertainty created by respiratory motion. Higher doses could increase the risk of gastrointestinal toxicity, such as gastric or duodenal mucositis, ulceration or perforation. There is also ongoing discussion on the appropriate delivered dose and potential dose escalation postoperativelly, especially in the pancreatic neck region above the standard dose of 27÷36 Gy in 3 fractions, what may reduce the rate of locoregional recurrences. Despite so many doubts, both the toxicity and the results of postoperative stereotactic radiotherapy are satisfactory. Early and late serious toxicity are limited and 2-year local control rate is beetwen 70÷80% and 2-year distant metastases-free survival is around 50% . Similar discussion takes place with regard to locally advanced cases but there is no specific effective dose established. There is a wide range of total delivered doses (24-40Gy) applied in variable dose fractions (6-12 Gy) and number of fractions (3-5). Systemic therapy plays an important role in the treatment of pancreatic cancer in both operable and inoperable pancreatic cancer. There is a group of patients, who can be treated with concomitant radiochemotherapy. It is also worth emphasizing that the use of stereotacic radiotherapy does not affect the ongoing chemotherapy and can be safely used between cycles of systemic treatment. Our experience also confirms that the effectiveness of stereotactic radiotherapy in locally advanced pancreatic cancer is high and the toxicity based on RTOG/EORTC scale is acceptable. In the present talk all- points will be summarized and the latest available data will be presented.

SP-0242 Current status and future perspectives of SBRT for lung tumours E. Troost 1 1 University Hospital Carl Gustav Carus, Radiotherapy and Radiation Oncology, Dresden, Germany

Abstract Text Stereotactic body radiotherapy (SBRT) has been successfully implemented in patients unfit or unwilling to