Abstract Book

S123

ESTRO 37

often young at diagnosis, with a median age of 5.5 years. At this age, radiotherapy can cause damage to all organs at risk in the head and neck area resulting in severe late adverse events. Furthermore, disruption of craniofacial bones may lead to asymmetrical or interrupted growth of the bony structures of the face, often further exacerbated by hypoplasia of soft tissues. In 1990, the AMORE approach was developed; Ablative surgery, MOulage brachytherapy, followed by REconstruction. AMORE proved to be equally effective compared to the international standard: external beam radiotherapy (EBRT). Moulage brachytherapy enables a focused dose delivery with relative sparing of healthy tissues causing fewer adverse events i.e., eye problems, pituitary insufficiency, speech problems, hearing loss, and musculoskeletal deformations compared to EBRT. Furthermore, growth deformation in AMORE and EBRT patients was further analyzed based on 3D stereophotogrammetry showing significant differences in facial surface area and curvature favoring the AMORE treatment group. The 3D image of both AMORE and EBRT treated patients was analyzed in comparison to a large healthy population. SP-0236 Late skin sequelae following skin applicator brachytherapy J.L. Guinot 1 1 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Valencia, Spain Abstract text Skin brachytherapy is an alternative or complement to surgery, with some advantages in dosimetry compared to external radiation techniques, but a standard optimal schedule of HDR is not well defined. Brachytherapy is simple and effective, with flaps, personalized moulds or surface applicators for superficial tumors up to 5mm. An interstitial approach should be used for tumours deeper than 5mm. Late skin sequelae are related with dosimetric factors as the dose per fraction, the depth of prescription, the extension of the radiated area and the total dose. The gradient of dose from the skin surface to the prescription dose points can have an influence on late changes. But also with anatomical factors, due to poor blood supply as tumours on the pinna, nose or scalp. Dose received by the skin blood vessels are crucial for the development of chronic sequelae. Main late effects involve cosmetic appearance, hypopigmentation, telangiectasia patchy pigmentation, hair loss and atrophy or fibrosis in the radiated area. Good cosmesis is always a goal but it is not so important for elder people. The expected results must be discussed with the patient to choose the best hypofractionated schedule for a good compliance. In general, an excellent or a good cosmetic result is obtained in 80-90% of patients after low dose rate brachytherapy (LDR), and over 90% with high dose rate (HDR). Skin necrosis or healing ulcer for lesions larger than 2 cm have been described in 5% with LDR. With HDR brachytherapy fewer series have been published, but G3-4 late sequelae are scarce.

intrafraction monitoring of the internal anatomy of the patient. During this presentation the basic principles of MRI will be first presented, thereby addressing the basic aspects of commissioning and quality assurance for in- room imaging in the implementation of an MR-guided radiotherapy program. Next, current MR protocols used for treatment planning in the realm of adaptive radiotherapy and real-time intrafraction visualization of soft-tissue structures will be discussed. Finally, perspectives for performing online functional imaging for dose response evaluation will be highlighted. 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Joint Department of Physics, London, United Kingdom Abstract text In clinical practice the majority of Image Guided Radiotherapy (IGRT) applications are currently based on in-room kV Cone Beam Computed Tomography (CBCT). In recent years inter-fraction adaptation strategies ranging from protocol based (daily or offline) re-positioning of the radiation target using the treatment couch, daily selection of an optimal treatment plan from a range of pre-optimized solutions and daily or weekly plan adaptation based on dose accumulation driven by deformable image registration have been investigated. With the introduction of MR Guided Radiotherapy (MRgRT) new methods have been develop to leverage the superior soft tissue contrast of MR imaging in high precision radiotherapy. The acquired MR images allow for daily adaptation of the treatment plan to improve the sparing of the organs at risk and for potential dose escalation to the tumour. Within this presentation the following topics related to daily replanning strategies using MR images will be addressed: - How to calculate dose on MR images? A brief overview of existing methods to derive synthetic CT images will be presented. - How to derive the necessary treatment planning contours on the MR images? - What daily plan adaptation methods are currently available or being researched? - What are the requirements for online plan QA? SP-0239 Intra-fraction variability and motion management R. Kashani 1 1 University of Michigan, Radiation Oncology, Ann Arbor MI, USA Abstract text Implementation of in-room MR image-guided systems (MRgRT) provides new opportunities in management of intra-fraction motion, using the target directly for gating, tracking, and potentially adapting the treatment plan in real-time. The superior soft-tissue contrast provided by MR, and the ability to acquire images continuously during treatment delivery without additional dose to the patient, allow us to better understand the various sources of motion and deformation within a treatment fraction, and to more accurately address these changes. Here we will discuss the commercially available MRgRT systems, their imaging capabilities, and the various proposed and implemented techniques for monitoring and correcting motion and deformation during the treatment. SP-0238 Daily replanning strategies S. Nill 1 , U. Oelfke 1

Symposium: New developments in online adaptive MRgRT

SP-0237 In room MR imaging M. Palacios 1 1 VU University Medical Center, Radiation Oncology Department, Amsterdam, The Netherlands Abstract text MR-guided radiotherapy provides superior soft-tissue visualization and provides the means for online inter- and