ESTRO 2021 Abstract Book

S551

ESTRO 2021

SP-0704 No ENI based on randomised evidence in NSCLC and SCLC S. Ramella1, C. Greco1, M. Fiore2, E. Ippolito2 1 Campus Bio-Medico University of Rome, Radiation Oncology, Rome, Italy; 2Campus Bio-Medico University of Rome, Radiation Oncology , Rome, Italy Abstract Text Despite the considerable progress made in recent periods in the treatment of locally advanced NSCLC thanks to the interaction of immunotherapy with chemoradiation, about 50% of patients have a survival of less than 4 years. Hence the goal of improving results by optimizing the therapeutic modalities available. In the PACIFIC study, the rate of progressions was 36.6% in the experimental arm versus 48.1% in the control arm (without immunotherapy). However, intrathoracic progressions appear even greater in the experimental arm than in the standard arm (80.6% vs 74.5%), probably due to the greater control of distant lesions. Consequently, it is clear that local disease control remains an area of great scientific interest to try to further improve these results. In order to have a term of comparison with the previously published studies, it is useful to report the definition of the nodal target volume in the RTOG 0617 study and in the PROCLAIM. In study RTOG 0617, the lymph nodes included in the target volume are both PET positive lymph nodes and lymph nodes with a minor axis greater than 1 cm on CT imaging. In the PROCLAIM study the definition of the target volume appears similar but not identical to the RTOG study, in fact the lymph nodes of the ipsilateral hilum were also added in the case of N2 disease. The publication of the PET-Plan study last year allows us to add some reflections regarding the definition of the target volume of the radiotherapy treatment. The study compared the use of conventional target definition (which includes both primary PET + tumor and PET + / biopsy + lymph node stations, and areas of atelectasis and positive CT-based lymph nodes) with an experimental arm in which the definition of the target volume is based exclusively on PET/biopsy positive. Locoregional progression at 1 year was 14% in the experimental arm versus 29% in the standard arm, at two years 20% versus 39% and at 3 years 23% versus 42%, thus showing a clear advantage in the possibility of doing an isotoxic dose escalation of the arm with limited PET-based volumes. The study's quality assurance data was recently reported at ESTRO 2020, which clearly show how the presence of major and relevant deviations to the contouring protocol affect both survival and locoregional progression of the disease. A further reflection comes from the randomized phase two PET-boost trial whose objective is to evaluate the best modality of delivery of the dose boost to the primary tumor. The goal of the study is freedom from local failure obtained by randomizing patients between a mode in which the boost is delivered to the whole primary tumor and a mode in which the boost is delivered to a PET-subvolume whithin primary tumor. The result showed an advantage for the boost to the entire primary tumor which at a median follow up of 12.6 months was 97% in this arm versus 91% in the PET-subvolume boost arm. This difference is also found in two years with percentages equal to 89% against 82%. The definition of the target volume for SCLC has seen a significant change over the years. Turrisi's study had already begun a process of reducing the target volume by defining the GTV on the basis of CT, including the mediastinum and the ipsilateral hilum but not the supraclavicular fossae. This progressive reduction of the target volume found its maximum expression in the phase III randomized CONVERT study where elective nodal irradiation was not permitted, although PET was not mandatory and the target volume was defined on the basis of CT imaging. SP-0705 Elective nodal irradiation still part of the standard treatment in head and neck cancer V. Grégoire 1 1 Leon Bérard Cancer Center, Radiation Oncology, Lyon, France Abstract Text This lecture will review the existing data justifying the international recommendations on node level selection and delineation for squamous cell carcinoma (SCC) of the oral cavity, oropharynx, larynx, hypopharynx and nasopharynx. It will also discuss these recommendations in light of the emergence of HPV-driven SCC. Last, it will discuss the more recent data on the use of imaging procedures aiming at optimising the selection of nodal levels to be treated as a function of the precise location of the primary tumor.

SP-0706 Pelvic nodal irradiation or no nodal pelvic irradiation in prostate cancer, that is the question A. Pollack USA

Abstract not available

SP-0707 Adjuvant nodal irradiation in breast cancer A. Kirby 1 1 Royal Marsden NHS Foundation Trust & Institute of Cancer Research, Radiotherapy, London, United Kingdom Abstract Text The role of adjuvant nodal irradiation in breast cancer has been evolving rapidly with a shift from axillary nodal clearance towards axillary nodal irradiation. This talk will review the data on axillary nodal irradiation and use cases to illustrate implications of these data for current treatment approaches.

Symposium: Recent developments in the treatment of rectal cancer