ESTRO 2021 Abstract Book

S348

ESTRO 2021

Monday 30 August 2021

Teaching lecture: Stem cells in radiation oncology

SP-0449 Stem cells in radiation oncology TBC

Teaching lecture: The microbiome: An emerging concept impacting the tumour and normal tissue with implications for treatment personalisation

SP-0450 The microbiome: An emerging concept impacting the tumour and normal tissue with implications for treatment personalisation A. Levy 1 1 Gustave Roussy, Radiation Oncology, Molecular Radiotherapy Lab, Villejuif, France Abstract Text Recent studies have provocatively claimed that the microbiome is present among cancers, and may influence both tumor control and normal tissue response, including to radiation therapy. Approaches that manipulate the host’s gut or tumor microbiome and possible implications in treatment personalization will be exposed.

Teaching lecture: Which techniques and delineation for craniospinal irradiation?

SP-0451 Which techniques and delineation for craniospinal irradiation? L. Padovani 1 1 Assistance Publique des Hôpitaux de Marseille , bouches du rhône, marseille, France

Abstract Text Which techniques and delineation for craniospinal irradiation ?

Craniospinal irradiation (CSI) is indicated for different rare brain tumors. For medulloblastoma (MB), CSI is part of the standard treatment for medulloblastoma maintaining the 5-year EFS higher than 80% for standard- risk MB and up to 70% for high-risk MB. However, this approach led to significant long-term radioinduced side effects, such as neuropsychological, hearing, and endocrine sequelae, particularly in very young children. In order to decrease the dose to the organs outside the target volume, different techniques of CSI have been investigated. Intensity-Modulated Radiation Therapy (IMRT), Tomotherapy and Volumetric Modulated Arc Therapy (VMAT) are highly conformal techniques, which can reduce the dose to the structures anterior to the vertebrae compared to 3D conformal radiotherapy technic. In a European multicentric dosimetric comparison study it is reported a reduction in mean dose of >5.0 Gy to organs such as the thyroid, heart, esophagus and pancreas. Research into pediatric CSI with proton therapy (Proton-CSI) has increased due to the physical advantage of proton to deliver the lowest possible dose to organ at risk and therefore the potential to reduce treatment-related toxicities. Compared to photontherapy it has been reported a decrease in mean dose (>5.0 Gy) for lenses, parotid- and submandibular glands, larynx, thyroid, lungs, heart, intestines, stomach and pancreas. The complexity of the growth of vertebrae makes the different technics of radiotherapy discuss in a goal to respect the volume of immature bone and decrease the late effects. In the area of high technologies of radiotherapy including protontherapy, guidelines are needed regarding vertebra target volume according the age and the sex. For medulloblastoma, the relationship between inadequate technique and patterns of relapse is clearly known, proved during the period of 3D conformal treatment. Therefore relapses were significantly increased when cribiform temporal or frontal lobes and thecal sac were excluded from the target volume. In a goal to reduce the risk of relapse because of new technical modality, it has been published guidelines for target craniospinal delineation. It is known that moving from classic 3 D conformal radiotherapy to IMRT or protontherapy induces risk of missing parts of some important structures if they are not delineated in the CTV. Moreover it has been highlighted that the cerebrospinal fluid flows beyond the inner table of the skull along the dural sheaths of cranial nerves. This finding led to be very carefully regarding the CTV definition which has to include all these structures and the delineation of whole subarachnoid space.

Teaching lecture: Treatment plan quality assessment

SP-0452 Treatment plan quality assessment V. Hernandez 1 , C. Rønn Hansen 2 , L. Widesott 3 , N. Jornet 4

1 Hospital Sant Joan de Reus, Medical Physics Department, Reus, Tarragona, Spain; 2 Laboratory of Radiation Physics, Odense University Hospital; Institute of Clinical Research, University of Southern Denmark, Danish Centre for Particle Therapy, Aarhus University Hospital, Denmark, Odense and Aarhus, Denmark; 3 Centro di protonterapia, APSS, Medical Physics Department, Trento, Italy; 4 Hospital de la Santa Creu i Sant Pau, Medical Physics Department, Barcelona, Spain

Abstract Text Plan evaluation is a key step in the radiotherapy treatment process. The goal of plan evaluation is to assess a