ESTRO 36 Abstract Book

S207 ESTRO 36 2017 _______________________________________________________________________________________________

healing ulcer. Another alternative is to extend the observation interval for an additional 1-2 months. Follow up – detection and treatment of regrowth Regrowths are inherently a part of the organ preservation approach, and follow-up should be aimed at early detection of local regrowth. The vast majority of local regrowths after W&W are located intraluminal and occur within 12-18 months. The backbone of local follow up is frequent examination by DRE and endoscopy during the first two years, supplemented by MRI to detect the less frequently occurring regrowths deeper in the bowel wall or lymph nodes. Our current schedule has a 3-4 monthly flexible sigmoidoscopy and MRI in the first year and 6 monthly thereafter until year 5. A TME is the best oncological option when a patient presents with a regrowth. Alternatives can be considered in various situations, such as a local excision of an isolated luminal regrowth in a patient with a high operative risk or patient preference to avoid major surgery and/or a definitive colostomy. Organ preservation series show that with adequate follow and early detection local regrowths occur in 15-25% and are mostly amenable to salvage treatment with good outcome. Conclusion Organ preservation constitutes a paradigm change with different treatment concepts: willingness to adapt the surgical plan according to the response, prolonging the observation time in good responders, the role of TME as salvage surgery, and expanding the role of patients in treatment choices. Although the risk seems low, there is no high-level evidence that organ preservation is as safe as standard TME surgery. This should be balanced against the possible benefits: avoidance of operative morbidity and mortality of a TME procedure, and an improved quality of life through. Because of a high interest of patients, the surgical community should cautiously move ahead and offer the option of organ preservation to patients in a controlled setting and combine this with providing further evidence. This can be achieved by setting up a prospective organ preservation protocol with standardized assessment and follow up in centers that add their data to a large multicenter database. At least initially it seems wise to concentrate organ preservation in a limited number of centers in order to gain sufficient expertise more quickly. SP-0389 Imaging and molecular profiles to predict response to chemoradiotherapy: where do we stand? K. Haustermans 1 1 UZ KUL, Department of Radiation Oncology, Leuven, Belgium The tumor response to preoperative chemoradiotherapy (CRT) is heterogeneous. About 20% of the patients achieve a pathological complete response (pCR). Patients with a pCR have a favorable long term outcome with excellent local control and disease-free survival. Adopting a watch and wait strategy in these patients is appealing since rectal cancer surgery entails complications, morbidity and even mortality. Strategies should be explored to precisely select patients who are candidates for a less invasive strategy. Conventional imaging lacks accuracy for restaging after CRT and is therefore not useful to select candidates for organ preservation. In recent years, there has been growing interest in molecular markers and functional imaging to improve clinical response assessment. Since immunity and inflammation play a critical role in tumorigenesis, inflammatory parameters might give useful information on the patient’s tumor response. Another promising strategy for the prediction of the response to CRT is the use of functional imaging. Diffusion-weighted imaging (DWI) and 18F-fluorodeoxy glucose positron emission tomography (FDG PET-CT) have emerged as promising tools in the prediction of tumor response before, during and after CRT. Besides the common parameters determined on these images such as

the Apparent Diffusion Coefficient (ADC) and the Standardized Uptake Value (SUV), tumor phenotypes can also be characterized by extracting a large number of quantitative image features (radiomics). A uniform prospective registration of patients with rectal cancer managed with a non-surgical approach will result in a detailed understanding of patient selection and will enable us to assess long-term outcome.

Symposium: Radiotherapy of brain tumours

SP-0390 Radiotherapy for low grade glioma in adults in 2017. What’s crazy! S. Villà Freixa 1 1 Catalan Institute of Oncology. Universitat Autònoma de Barcelona, Radiation Oncology, Badalona. Catalonia, Spain Diffuse low grade glioma (LGG) is a heterogeneous group of tumors in terms of survival. Maximal surgical resection is the initial optimal treatment but no clear evidences have been published. Adjuvant treatment using radiotherapy (RT) and chemotherapy has been used in high risk patients and a significant improvement of survival has been shown. RT plays a key role in the RTOG series but timing, volumes and dose are still undefined. After the final results of EORTC 22033 and RTOG 98-02 trials it has been suggested that chemotherapy is active for LGG. Indeed, chemotherapy did not imply a decline in MME score in the American trial. Nowadays however the main argument for delaying RT in patients with LGG is to avoid neurocognitive and quality of life deteriorations. Nevertheless, no significant differences in quality of life were reported between RT and temozolomide groups in the EORTC 20033 trial when analysis of the questionnaires were done, with acceptable level of compliance. Notably, median progression free survival for patients in the RT group was superior to chemotherapy group (not significant). In the new era of molecular biology for gliomas with its prognostic potential role, it is important to underlay that the major strength of EORTC 22033 trial was that molecular data ( IDH 1/2 , 1p/19q co-deletion) were available in more than 80% of patients (45% of patients in the RTOG 98-02 trial). RT seemed to be as effective as temozolomide in patients with IDH1 or IDH2 mutations and 1p/19q co-deletion. For Radiation Oncology community, it is pending to solve several questions: 1- Defining volumes (GTV, CTV, PTV), and protecting hippocampus using co-registrations with CT, different sequences of MRI and PET scan. 2- Using new modifications of IMRT (as VMAT) or protontherapy as standard. 3- Determining dose fractionation and total dose, taking into account that the standard EORTC dose of 50.4 Gy has not been compared with lower total dose. In conclusion, it seems that in high risk LGG patients the combination of RT with chemotherapy improves survival and progression free survival and that RT is comparable to temozolomide. However, Radiation Oncology community has to step forward in defining techniques and total dose and fractionation. SP-0391 What is the role of combined chemo- radiotherapy for grade III glioma in adults? A. Chalmers 1 1 Inst. of Cancer Sciences-Univ. Glasgow The Beatson West of Scotland Cancer Center, Department of Clinical Oncology, Glasgow, United Kingdom Classification, prognosis and treatment of grade III glioma is now determined predominantly by molecular biomarkers, with 1p19q chromosomal co-deletion conferring a clear prognostic benefit and also being associated with better response to chemotherapy. The