E.M. Kerkhof

Can we Save the rectum by watchful waiting or TransAnal microsurgery following (chemo) Radiotherapy versus Total mesorectal excision for early REctal Cancer (STAR-TREC study)?: protocol for a multicentre, randomised feasibility study

Introduction Total mesorectal excision (TME) is the highly effective standard treatment for rectal cancer but is associated with significant morbidity and may be overtreatment for low-risk cancers. This study is designed to determine the feasibility of international recruitment in a study comparing organ-saving approaches versus standard TME surgery. Methods and analysis STAR-TREC trial is a multicentre international randomised, three-arm parallel, phase II feasibility study in patients with biopsy-proven adenocarcinoma of the rectum. The trial is coordinated from Birmingham, UK with national hubs in Radboudumc (the Netherlands) and Odense University Hospital Svendborg UMC (Denmark). Patients with rectal cancer, staged by CT and MRI as ≤cT3b (up to 5 mm of extramural spread) N0 M0 can be included. Patients will be randomised to either standard TME surgery (control), organ-saving treatment using long-course concurrent chemoradiation or organ-saving treatment using short-course radiotherapy. For patients treated with an organ-saving strategy, clinical response to (chemo)radiotherapy determines the next treatment step. An active surveillance regime will be performed in the case of a complete clinical regression. In the case of incomplete clinical regression, patients will proceed to local excision using an optimised platform such as transanal endoscopic microsurgery or other transanal techniques (eg, transanal endoscopic operation or transanal minimally invasive surgery). The primary endpoint of this phase II study is to demonstrate sufficient international recruitment in order to sustain a phase III study incorporating pelvic failure as the primary endpoint. Success in phase II is defined as randomisation of at least four cases per month internationally in year 1, rising to at least six cases per month internationally during year 2. Ethics and dissemination The medical ethical committees of all the participating countries have approved the study protocol. Results of the primary and secondary endpoints will be submitted for publication in peer-reviewed journals. Trial registration number ISRCTN14240288, 20 October 2016. NCT02945566; Pre-results, October 2016.

Evaluation of clinical and endoscopic toxicity after external beam radiotherapy and endorectal brachytherapy in elderly patients with rectal cancer treated in the HERBERT study

INTRODUCTION The HERBERT study evaluated a high-dose-rate endorectal brachytherapy boost (HDREBT) after EBRT in medically inoperable/elderly patients with rectal cancer. The response-rates are promising but not without risk of toxicity. The current analysis provides a comprehensive overview of patient reported, physician reported and endoscopically observed toxicity. MATERIAL AND METHODS A brachytherapy dose finding study was performed in 38 inoperable/elderly patients with T2-T4N0-1 rectal cancer. Patients received EBRT (13 × 3 Gy) followed by three weekly HDREBT applications (5-8 Gy). Toxicity was assessed via three methods: patient and physician (CTCAEv3) reported rectal symptoms and endoscopically. Wilcoxons signed rank test, paired t-test and Spearmans correlation were used. RESULTS Patient reported bowel symptoms showed a marked increase at the end of EBRT and two weeks after HDREBT. Acute grade 2 and 3 proctitis occurred in 68.4% and 13.2% respectively while late grade 2 and ≥3 proctitis occurred in 48% and 40%. Endoscopic evaluation mainly showed erythema and telangiectasia. In three patients frank haemorrhage or ulceration occurred. Most severe toxicity was observed 12-18 months after treatment. CONCLUSION For elderly patients with rectal cancer, definitive radiotherapy can provide good tumour response but has a substantial risk of toxicity. The potential benefit and risks of a HDREBT boost above EBRT alone must be further evaluated.

PO-0846: MR-based adaptive radiotherapy for cervical cancer: A concept of fast, automated IMRT planning

PO-0845 Evaluation of interplay effects of target and MLC during VMAT by using 3D gel measurements S. Ceberg, C. Ceberg, M. Falk, P. Munck af Rosenschöld, S. Bäck Skåne University Hospital, Medical Radiation Physics, Lund, Sweden Lund University, Medical Radiation Physics Department of Clinical Sciences Lund, Lund, Sweden Radiation Medicine Research Center, Radiation Oncology Rigshospitalet, Copenhagen, Denmark

INTEGRATED 1.5 T MRI AND ACCELERATOR: PROOF OF CONCEPT FOR REAL-TIM E MRI GUIDED RADIOTHERAPY

INTEGRATED 1.5 T MRI AND ACCELERATOR: PROOF OF CONCEPT FOR REAL-TIME MRI GUIDED RADIOTHERAPY B. Raaymakers1, J. Lagendijk1, J. Overweg2, J. Kok3, A. Raaijmakers1, E. Kerkhof1, R. van der Put3, I. Meijsing1, S. Crijns1, F. Benedosso3, M. van Vulpen1, N. de Graaff3, J. Allen4, K. Brown4 1 UMC UTRECHT, Department of Radiotherapy, Utrecht, Netherlands 2 PHILIPS, Hamburg, Germany 3 UMC UTRECHT, Utrecht, Netherlands 4 ELEKTA UK LIMITED, Crawley, West Sussex, United Kingdom

SU‐GG‐J‐60: Constructing a 6 MV Radiotherapy Accelerator with Integrated 1.5T MRI functionality: Status Report

Radiotherapy is increasingly dependent on image data for treatmentpreparation, delivery, response assessment and follow‐up. In collaboration with Elekta, Crawley, UK and Philips, Best, The Netherlands, we are constructing a hybrid 1.5T MRIradiotherapy system. This system facilitates real‐time, soft‐tissue based image guidance during delivery as well as treatment response assesment. The preceeding technical feasibility study led to a design in which the 6MV accelerator can rotate in a ring around the MRI in the mid‐transversal plane. The magnet design is adjusted in order to minimise the magnetic interference and to minimise the absorption of the beam. The prototype is planned for autumn 2008. The aim is to demonstrate MRI guided radiation with sub‐mm precision. The prototype will initially be static: the accelerator will be in a fixed lateral position. The treatment room preparation will be discussed including: creation of entrance route in bunker, faraday cage, cooling and electrical connections for in‐room MRI peripherals and passive magnetic room‐shielding to minimise magnetic interference with neighbouring clinical accelerators.The current Geant4 Monte Carlo simulations on the accelerator output and radiation dosimetry will be verified in the prototype. Geant4 simulations were also used to find suitable IMRT solutions in the presence of a 1.5T field, these will be evaluated experimentally. System related issues addressed will be the radiofrequency interference between the MRI and the accelerator, the geometric correction of images dedicated for this system and the geometrical coupling of the MRI and accelerator coordinate system. Also the automatic, on‐line target definition on MRI and the clinical benefit of MRI guidance will be discussed.