ESTRO 2021 Abstract Book

S164

ESTRO 2021

images with large tumours (accuracy of 70%) compared to smaller tumours (accuracy 96%). Large tumours can cause stromal oedema by tumour compression or inflammation and this must be considered when making treatment decisions in these patients. MRI including DWI is excellent for tumour delineation prior to external beam radiotherapy (EBRT) playing a crucial role in precise treatment planning. It is routinely used to evaluate response to EBRT thus facilitating patient selection for and planning of brachytherapy treatment. The reconstitution of low signal intensity cervical stroma on T2WI and the absence of restricted diffusion on DWI are the best indicators of disease-free cervix. MRI is also used to monitor the placement of brachytherapy probe as well as evaluate treatment response to brachytherapy. Finally, it is the best tool to evaluate for presence of tumour recurrence in the radiotherapy treated cervix. In conclusion, MRI is an essential tool along the entire journey in patient with cervical cancer with the radiologist playing a crucial role in the disease management team and providing very valuable input in the multi-disciplinary team meetings. SP-0246 MR-linac in gynaecological tumours: Looking for added values L. Boldrini 1 1 Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Rome, Italy Abstract Text MR guided radiotherapy represents one of the most promising recent innovations in the field of radiation oncology. Unfortunately, due to the limited number of active hybrid units the clinical evidence about indications and possible roles is scarce and far to be completely governed. Aim of this talk is to become familiar with MR-linac treatments for gynaecological cancers, focusing on the added values of online adaptive treatment approaches, possible predictive applications of online hybrid images (i.e. radiomics), and future developments and integration opportunities. SP-0247 MR anatomy of the uterus, cervical and pelvic floor: All you need to know for accurate contouring S. Nougaret France Abstract not available

SP-0248 Image-guided adaptive brachytherapy in gynaecological tumours R. Nout The Netherlands

Abstract not available

Joint symposium: ESTRO-EFOMP: New radiotherapy technology - What does it mean for radioprotection

SP-0249 Radiation protection in proton therapy facilities

H. Nyström 1

1 The Skandion Clinic, Medical physics, UPPSALA, Sweden

Abstract Text Safety is one of the most important aspects of radiotherapy (RT). High doses are distributed to patients whereas the acceptable levels to the employee and general public is still as low as in other areas of the society. Radiation protection is a fundamental aspect of the RT procedure and is an inherent part of the whole process; from the design of the clinic, over choice of equipment to all the daily procedures of the clinic. Basically, radiation protection in proton therapy (PT) is not much different than for conventional RT. Keeping the dose levels low to staff and non-patients is uncomplicated and the focus is concentrated to avoid incidents, accidents and risky situations. There are, however, two important differences which deserves attention. The first is that protons can activate the matter they are interacting with, resulting in background radiation after the beam is turned off. For the clinical staff this is less of a problem but should be considered when designing the clinical workflow. For the technical staff taking care of the equipment, activation is of major concern and will significantly contribute to the dose received. The second difference is the production of neutrons, some of quite high energy. Neutrons and activation are also present in conventional RT if energies higher than 10 MV are used, but the amount is far lower than what can be found in PT. Neutrons are basically taken care of in the design of the facility with thick enough shielding and appropriate composition of the shielding materials. Activation, on the other hand, may call for adapted procedures and workflow to minimize the exposure of the staff, in particular for the technical personel. Radiation protection is of course primarily a matter of safety and to reduce unintended exposure of humans, including the patient. However, to a large extent it is also about the legal procedure to achieve all the necessary permits and to please the regulatory authorities. Without permission from the authorities, no proton treatment. Sometimes the national regulatory authorities lack knowledge and competence to properly understand the vital aspects of PT and may sometimes focus on totally irrelevant aspects that may cause the PT clinic serious concerns. As an example, can be mentioned the air activation caused by the PT clinic. Such