ESTRO 38 Abstract book

S114 ESTRO 38

provided to show insight in factors that influences stem cells functioning and how this may be used to enhance post-irradiation tissue regeneration and consequential retreatment tolerance. SP-0223 Protons, stereotactic radiotherapy and adaptive radiotherapy – what is their value for reirradiation? A. Richter 1 1 Universitätsklinikum Würzburg, Department of Radiation Oncology, Würzburg, Germany Abstract text For re-irradiation highly conformal treatment techniques are needed. Some technological developments such as proton therapy, stereotactic and adaptive radiation therapy have improved targeting accuracy and offer the possibility of highly conformal dose distributions. For proton therapy, the low exit dose is advantageous to achieve a high degree of dose conformity. The availability of proton therapy is limited to proton centers. The wider availability of in-room imaging and advanced treatment delivery systems means that more institutions are now offering stereotactic radiation therapy. The stereotactic approach uses an inhomogeneous dose distribution with a sharp fall-off dose and tight margins to achieve a high biological effective dose in the target and a dramatic sparing of normal tissue. For both techniques (proton and stereotactic radiotherapy), motion management strategies should be implemented to considered interfraction and intrafraction motion. Adaptive radiation therapy accounts for changes in patient’s anatomy and/or physiology during the treatment course. The adaptive radiation therapy is based on repeated anatomical and/or functional imaging and the use of deformable image registration. Further elements of the adaptive workflow are the automatic recontouring, plan evaluation and reoptimization, dose calculation, and quality assurance. Adaptive radiation therapy can be performed in real-time, online or offline. The clinical realization of online adaptive radiotherapy is extremely challenging, mainly due to the inability for real-time treatment re-planning. The implementation of adaptive radiotherapy presents some challenges such as accuracy of deformable image registration and the higher workload for the staff. Despite some challenges, proton and stereotactic radiation therapy offer the possibility of highly conformal dose distributions. Adaptive radiation therapy holds significant promise in maximally compensating for intra and interfraction anatomical uncertainties. SP-0224 Brachytherapy in the reirradiation situation – what are benefits and limitations compared to modern EBRT? C. Gutiérrez Miguélez 1 1 Institut Català d'Oncologia, Brachytherapy Unit, L'Hospitalet de Llobregat, Spain Abstract text In this talk, I will do a revision of indications of Brachytherapy for reirradiation, a revision of the results in published in the literature and our results in different locatizations. In the last years, due to the advances in imaging and dosimetry optimizacion, the interest and use of Brachytherapy (BT) for treating relapses is growing. The benefits of reirradiation with Brachytherapy versus External Radiotherapy (ERT) are: Smaller treated volume; Accuracy: no motion; Rapid dose fall-off; Accelerated treatment (therapeutic gain); Preferably intraoperative approach; If intra/peroperative implant, only 1 procedure. The limitations or disadvantages would be: Very small treated volumen; Operator dependent; Need of skills to insert applicator; Need of Operating Theatre; Help of other especialits (surgeons); Inhomogeneous dose distribution (Hot spots);

disease and response to therapies, ultimately enabling highly precise interventions with high efficacy and less side effects. Mathematical and computational modelling techniques developed by systems biology to analyse dynamic living systems play a key role in achieving these goals. I will discuss the role of such models for precise diagnostic stratification, the identification of efficacious drug combinations, and the personalisation of treatment.

Symposium: Balancing the risks and benefits of re- irradiation

SP-0221 Indications for re-irradiation – changes in the era of effective systemic treatment options? M. Hoyer 1 1 Aarhus University Hospital, Danish Center For Particle Therapy, Aarhus, Denmark Abstract text The recent years have brought a number of drugs directed towards novel targets of the cancer cells. Many of these have given led to some improvement of the survival. This survival gain is moderate in most cancers, but it may a reason for reconsideration of strategies in treatment of radio-recurrent cancer? Reirradiation is always related to an increased risk of complication and selection of patients for reirradiation represents a delicate balance bestween disease control and survival gains on one hand and risk of severe complication on the other. The presentation will give examples of considerations in selection of radio-recurrent patients for reirradiation. However, it will conclude that systemic therapies cannot replace radiation therapy in the attempt to achieve long lasting tumor control. SP-0222 Radiobiology of normal tissue repair – what are the implications for reirradiation? R. Coppes 1 1 University Medical Center Groningen, Radiation Oncology and Cell Biology, Groningen, The Netherlands Abstract text The response of normal tissues to irradiation is mainly determined by the survival and regenerative potential of the tissue stem cells, and modulated by inflammatory processes, vasculature damage and altered neuronal innervation and fibrosis. Interestingly, transplantation of tissue specific stem cells has been shown to restores tissue homeostasis and sparing stem cells may preserve tissue function and prevent late radiation effects. It is for long recognized that the number of surviving clonogens determines the time to recovery after irradiation and with that also the retreatment tolerance of many tissues. Since these clonogens are often stem cells or derived progenitor it seems eminent to spare these as much of possible to reduce normal tissue side effects and potentially allow reirradiation when needed. Recently much improvement has been made to described and characterized the tissues stem cells. This now allows localisation and studying of radiation responses in vitro and in vivo. In combination with accurate localised tissue proton irradiation this has yielded novel insight in the regenerative processes of several tissues. Dose volume effects, inhomogeneous irradiation field and uneven distribution of stem cells greatly influences the regenerative potential and with that the retreatment tolerance of normal tissue. Moreover, studies of post irradiation form in tissue isolated stem cells show regenerative potential in vitro being much higher than in situ, indicating that not only the radiation damaged stem cells themselves determine regenerative potential but also the affected environment. In this presentation the radiobiology of reirradiation will be discussed and examples of several tissue will be