Abstract Book

S344

ESTRO 37

PC, Heijmen BJM. Toward Fully Automated Multicriterial Plan Generation: A Prospective Clinical Study. Int J Radiat Oncol Biol Phys. 2013; 85(3): 866-72. 3. Voet PW, Dirkx ML, Breedveld S, Al-Mamgani A, Incrocci L, Heijmen BJM Fully Automated Volumetric Modulated Arc Therapy Plan Generation for Prostate Cancer Patients. Int J Radiat Oncol Biol Phys. 2014; 88(5):1175-9 4. Sharfo AW, Breedveld S, Voet PW, Heijkoop ST, Mens JM, Hoogeman MS, Heijmen BJ. Validation of Fully Automated VMAT Plan Generation for Library-Based Plan- of-the-Day Cervical Cancer Radiotherapy. PLoS One. 2016; 11(12): e0169202. 5. Della Gala G, Dirkx ML, Hoekstra N, Fransen D, Lanconelli N, van de Pol M, Heijmen BJM, Petit SF. Fully automated VMAT treatment planning for advanced-stage NSCLC patients. Strahlenther Onkol. 2017;193(5):402-409. SP-0648 Challenges for clinical automated planning encountered at Odense University Hospital C. Hansen 1 1 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark Abstract text Treatment planning is often highly complex due to multiple dose prescription levels and numerous organs at risk. Automatic planning can help in the process of creating a deliverable plan, which handles the many issues that constitutes a plan of high quality. Automatic plan generation has been performed at Odense University Hospital (OUH) since 2015 by use of Autoplan from Pinnacle for more than 1000 patients. Autoplan has been used within almost all treatment sites; H&N, prostate, brain, bladder, esophagus, cervix, lymphomas – in descending order of number of patients treated. For most of the treatment sites, there was a clear gain in dose reduction to the majority of the organs at risk (OAR), a general increase in overall plan quality while the user time decreased. Some of the challenges have been to find treatment techniques that could handle overlapping targets and organs at risk specifically for brain and prostate treatments. Also the fact that Autoplan uses the RTOG prescription, where 95% of the target volume receives 100% of the prescription dose, which is different form the ICRU recommendation of 95% of the prescription dose to 100% of the target volume has caused some challenges. In areas of high density differences, like the lung, the automatic plan generation can encounter problems. Automatic treatment planning can be used to incorporate new clinical trial protocols, where the protocol concept can be foreign to the individual centres. In a study across three centres internationally, each centre were asked to implement two new protocols using Autoplan and test if the plan quality was sufficiently high for use in a trial. The talk will focus on some of these challenges and try to describe some of the clinical gains seen at Odense University Hospital due to higher plan quality.

Symposium: Advances in normal tissue radiobiology

SP-0649 Hyperbaric oxygen therapy for the treatment of the late effects of radiotherapy J.R. Yarnold 1 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Radiotherapy & Imaging Department, Sutton, United Kingdom Abstract text Improvements in tissue healing and patient benefit after hyperbaric oxygen (HBO) in patients suffering late onset adverse effects (AE) have been reported in a large number of retrospective studies and prospective single arm cohort studies since the mid-1970s. Multiple sources of bias undermine the robustness of these sources of evidence categorised as Level II and allowing only Grade B recommendations for treatment. Marx conducted a pioneering randomised clinical trials (RCT) in the 1980s & ‘90s comparing HBO with standard surgery for mandibular osteoradionecrosis (ORN) in patients following radiotherapy (RT) for head and neck cancer, reporting statistically and clinically significant improvements in complete mucosal cover(1, 2). Serial transcutaneous oxygen measurement over the cheeks of patients confirmed substantial recovery of soft tissue oxygen tension, subsequently confirmed in experimental animal systems to correlate with neoangiogenesis. Despite this very promising start, the subsequent history of HBO research has not built a solid evidence base for the use of HBO in standard practice, even though it remains in use. A 2016 Cochrane systematic overview identified 17 RCT, of which 14 were eligible for qualitative synthesis, leaving only 3 suitable for metanalysis; a 4 th has since been published(3). The only RCT in patients with ORN failed to reproduce earlier positive findings(4). A double-blind, sham-controlled RCT of patients with proctitis reported statistically and clinically significant improvements in physician assessed bowel symptoms and in patient-reported ‘bowel bother’ 3 months post-HBO, but later assessments were confounded by a cross-over design offering HBO to non- responding, sham-treated patients(5). A second double-