Abstract Book

S180

ESTRO 37

arising from exceeding adjacent critical organ tolerance doses. A patient selection procedure has been developed with a nation-wide consensus in order to specify the workflow for an inter-clinic photon-proton plan comparison and to define the relevant target coverage criteria, NTCP models and delta-NTCP thresholds which will be used to indicate eligibility for proton therapy. The presentation will consist of: o an overview of the patient selection procedure and plan comparison workflow o a demonstration of the proton planning process at the UMCG, including robust optimisation, evaluation of target coverage under uncertainties, and calculation of NTCP o a summary of planning comparison results since clinical operation o advanced tools and further work in development SP-0342 Carbon ion therapy in adenoid cystic carcinoma A. Jensen 1 1 University of Munich, Radiation Oncology, München, Germany Abstract text Due to their aggressive local growth patterns, adenoid cystic carcinomas require high radiation doses in order to achieve long-term local control. Unfortunately, patients with salivary gland malignancies are often diagnosed with advanced disease; especially in the paranasal sinuses both surgical and radiooncological approaches remain a challenge in view of close proximity to critical structures. In the 1980s, radiotherapy with neutrons and hence high- LET radiation resulted in superior local control rates but observed long-term toxicities were substantial. Charged particle beams with carbon ions (C12) also show increased radiobiological effectiveness as compared to photon RT. In contrast to neutron radiation though, they exhibit sharp dose gradients leading to highly conformal dose distributions with improved normal tissue sparing especially at complex anatomical sites. Therefore, carbon ion therapy (C12) in the treatment of adenoid cystic carcinoma has been intensively investigated by both Japanese and European groups. Recent analyses show significantly improved control and survival rates in patients treated with a combination regimen of C12 plus IMRT vs IMRT only. In patients with T4 tumours treated with C12, control rates did not differ according to resection status indicating that debulking surgery with sometimes substantial morbidity may not be necessary. Results were confirmed by the prospective COSMIC trial and validated in a larger patient cohort. In the head and neck in general and in ACC in particular, management of local recurrence following full course radiotherapy remains an oncological challenge. Chemotherapeutic regimen only achieve limited response rates if there are no surgical options. High-dose re- irradiation with charged particles can be feasible and achieves promising response rates with moderate toxicity. However, further dose escalation needs to be considered carefully as the risk of higher-grade late toxicity increases. In summary, particle therapy is a good treatment option with promising local control especially in advanced ACC. The use of tumour debulking surgery in advanced ACC may have to be reconsidered. In cases of local tumour relapse, C12 may be a good option when surgery is not feasible but has to be used with caution.

Debate: This house believes that 5x5 Gy offers more opportunities for tailor made treatment than conventional chemoradiotherapy in rectal cancer patients

SP-0343 For the motion F. Peters LUMC, Leiden, the Netherlands

Abstract not received

SP-0344 Against the motion M.A. Gambacorta 1 , G. Chiloiro 1 , A. Re 1 1 Università Cattolica del Sacro Cuore, Radiation Oncology, Rome, Italy

Abstract text Introduction Preoperative radiotherapy represents the standard treatment in locally advanced rectal cancer. Two main modalities of delivery are currently used: short course radiotherapy and long course chemoradiation. Both these modalities have as main objective to decrease the rate of local failure. The standard way to deliver preoperative chemoradiation is administration of a 45-50 Gy approximately 5 weeks, with a standard fractionation of 1.8-2Gy a day, with concomitant 5FU based chemotherapy. From the technical point of view standard chemoradiation can be delivered on the tumor and elective CTV with a single field or on the elective CTV followed by a boost directed to the tumor. After 6-8 weeks the patient is re-staged and undergo to radical surgery. Material and methods The standard chemoradiation, due to its characteristic of delivery, permits to achieve tumor downstaging as well as decreasing local failure. This allows to treat more advanced tumor leading to higher possibility of surgery with clear margin. Moreover, tumor response to treatment, may add important information to stratify patients at different prognosis. As an example there is a 15-20% of complete responder tumors at pathology. In these subgroup of patients, retrospective pooled analyses, showed better long term outcomes compared to the not complete responders. Tumor response may be finally attributed to total dose, concomitant chemotherapy intensification and interval between the end of chemoradiation and surgery. These characteristics of chemoradiation can be used to tailor the treatment according tumor presentation and expected results. I.e. studies tried to improve tumor response by adding a second drug to concomitant chemotherapy achieving good results in several phase 2 trials, although not completely confirmed in phase 3 trials, some other studies obtained better results in term of pathological complete response by the intensification of radiotherapy dose both with concomitant or simoultaneous integrated boost, nowadays several phase 2 studies are focusing on the prolongation of interval between chemoradiation and surgery to achieve better response overall demonstrating higher response after 14- 16 weeks compared with the standard 6-8 weeks. Other field of research are trying to achieve not only better response but also better DFS in patients at higher risk of metastases or to treat oligometastatic patients. By the addiction of chemotherapy in the neoadjuvant setting both before than after chemoradiation (TNT: Total Neoadjuvant Therapy), researchers are trying to decrease the rate of distant relapses that since now still represents the major cause of tumor death in rectal cancer or to conteporraly treat patients of the primary tumor site and on the distant site.