ESTRO 37 Abstract book

S341

ESTRO 37

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.

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- blind, sham-controlled RCT of HBO versus best standard care in patients with radiation proctitis failed to confirm these benefits, reporting comparable improvements in patient-reported rectal bleeding in both HBO and sham- treated groups(6). HBO is a cumbersome intervention but high quality hyperbaric medicine facilities exist in many countries. The risks of HBO are small provided standard precautions are taken and well-established procedures are followed. The moderate economic costs would makes HBO a very cost-effective intervention, but only if the research community succeeds in generating a more substantial body of high quality evidence. References 1. Marx RE, Johnson RP, Kline SN. Prevention of osteoradionecrosis: a randomized prospective clinical trial of hyperbaric oxygen versus penicillin. J Am Dent Assoc. 1985;111(1):49-54. 2. Marx RE. Hyperbaric Medicine Practice: Chapter 23, Radiation Injury to Tissue. Hyperbaric Medicine Practice. Second ed: Best Publishing Company; 1994. p. 448-501. 3. Bennett MH, Feldmeier J, Hampson NB, Smee R, Milross C. Hyperbaric oxygen therapy for late radiation tissue injury. Cochrane Database Syst Rev. 2016;4:CD005005. 4. Annane D, Depondt J, Aubert P, Villart M, Gehanno P, Gajdos P, et al. Hyperbaric Oxygen Therapy for Radionecrosis of the Jaw: A Randomized, Placebo- Controlled, Double-Blind Trial From the ORN96 Study Group. J Clin Oncol. 2004. 5. Clarke RE, Tenorio LM, Hussey JR, Toklu AS, Cone DL, Hinojosa JG, et al. Hyperbaric oxygen treatment of chronic refractory radiation proctitis: a randomized and controlled double-blind crossover trial with long-term follow-up. Int J Radiat Oncol Biol Phys. 2008;72(1):134- 43. 6. Glover M, Smerdon GR, Andreyev HJ, Benton BE, Bothma P, Firth O, et al. Hyperbaric oxygen for patients with chronic bowel dysfunction after pelvic radiotherapy (HOT2): a randomised, double-blind, sham-controlled phase 3 trial. Lancet Oncol. 2015. SP-0650 Advances in clinical radiobiology: modelling of normal tissue complication probability R. Pacelli 1 1 Università "Federico II" di Napoli, Scienze Biomediche Avanzate, Napoli, Italy Abstract text Clinical radiobiology may be defined as the study of the action of ionizing radiations on human being considering clinical relevant endpoints. Tumor control and normal

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