ESTRO 2023 - Abstract Book

S160

Saturday 13 May

ESTRO 2023

Conclusion Two thirds of all HNC patients had a replan, and approximately two thirds of these were for dosimetric reasons. Almost half of patients replanned for dosimetric reasons had underdosage in all 3 CTVs. The largest underdosed volumes were found in CTV3, while the smallest underdosed volumes were seen in CTV1. The underdosed volumes for CTV1 and 2 were generally less than 0,5 cm3 for more than 75% of all cases. These results suggest that the applied replanning strategy was adequate and may form the basis for development of objective replanning thresholds. MO-0226 Functional lung preservation during stereotactic body radiotherapy guided by perfusion PET/CT F. Lucia 1 , M. Hamya 2 , F. Pinot 3 , G. Goasduff 2 , F. Blanc-Béguin 3 , D. Bourhis 4 , O. Pradier 2 , A. Lucia 2 , S. Hennebicq 3 , M. Mauguen 2 , R. Floch 3 , U. Schick 2 , V. Bourbonne 2 , P. Salaun 3 , P. Le Roux 3 1 University Hospital, Brest, Radiation Oncology , Brest, France; 2 University Hospital, Radiation Oncology, Brest, France; 3 University Hospital, Nuclear Medicine, Brest, France; 4 University Hospital, Nuclear Medicine, Brest, France Purpose or Objective Stereotactic body radiation therapy (SBRT) has become a real alternative treatment for inoperable stage I-II non-small cell lung cancer and lung oligometastases with a high local tumor control rate. However, SBRT remains associated with significant pulmonary toxicity. The aim of this study was to assess the feasibility to spare functional lung areas by integration of pulmonary functional mapping guided by Gallium-68 perfusion PET/CT imaging in lung SBRT planification. Materials and Methods We conducted a single-center prospective study. Patients planned to receive SBRT for primary of secondary lung tumors were eligible. All patients underwent a lung 68Ga perfusion PET/CT. Lung functional volumes were defined as the minimal volume containing 50% (FV50%), 70% (FV70%) and 90% (FV90%) of the total activity within the anatomical volume. All patients had a treatment planning carried out in 2 stages: an anatomical planning blinded to the PET results, then a functional planning, respecting the standard constraints, but also incorporating "lung functional volume" constraints. The mean lung dose (MLD) in functional volumes and the percentage of lung volumes receiving 5, 10, 15 and 20 Gy (VxGy) within the lung functional volumes using both plans were calculated and compared.