ESTRO 2022 - Abstract Book

S1071

Abstract book

ESTRO 2022

Results 25 LA-NSCLC elderly patients unfit for concurrent and/or sequential ChT-RT were recruited. Median age was 81 years (range,72-89) and 15 (60%) were male. Histology was adenocarcinoma (ADK) and squamous cell carcinoma (SCC) in 17 (68%) and 8 (32%), respectively. The stage was IIB, IIIA and IIIB in 9(36%), 11(44%) and 5(20%) patients, respectively. All patients had ultra-central tumor with PTV overlapping the major airways. In 8 (32%) cases T and N were separately treated using SIB technique to administer a higher dose to T. Median prescribed dose was 40 Gy (range, 35-50) and 40 Gy (35-45) in 5 fractions to T and N, respectively. During a median follow-up of 18 months (range, 4-71) 6 (24%) and 7 (28%) patients had experienced isolated local recurrence and nodal regional recurrence at a median time of 9 (range, 7-17) and 9 months (range, 4-17), respectively. 5 (20%) patients developed distant metastases after a median time of 11 months (range, 4- 26). At last follow-up, 19 (76%) patients were alive, 11 (44%) without radiological evidence of disease. Treatment compliance was 100% and no patients developed ≥ G3 acute and late toxicities. Conclusion LA-NSCLC elderly patients treated with exclusive SABR had optimal local control and promising overall survival with excellent treatment compliance and absence of ≥ G3 toxicity. Our preliminary prospective clinical outcomes provide an attraction to evaluate this approach in elderly patients unfit to ChT, to obtain a “big” cure beyond “little” palliation. 1 University Hospital, Radiation Oncology, Brest, France; 2 Université de Bretagne Occidentale, LaTIM, UMR 1101 INSERM, Brest, France; 3 Institut Mines, Télécom Atlantique, Brest, France Purpose or Objective In patients treated with radiotherapy for a locally advanced lung cancer, respect of dose constraints to organs at risks (OARs) insufficiently protects patients from acute pulmonary toxicity (APT), such toxicities being associated with a potential impact on treatment’s delivery and the patients’ quality of life. Daily dosimetric planning does not take into account regional lung functionality. An APT prediction model combining usual dosimetry features with the mean dose (DMean Pmap ) received by a voxel-based volume (Pmap) localized in the posterior right lung has been previously developed. A DMean Pmap > 30.3Gy was associated with a higher risk of APT. In this study, the authors aim to demonstrate the possibility of decreasing the DMean Pmap via a VMAT-based adapted planning and evaluate the consequences on the risk of APT. Materials and Methods Among the 207 patients included in the initial study, only patients that presented with a APT ≥ grade 2 and with a probability of APT (Prob APT ≥ 8%) based on the prediction model were included. Dosimety planning was optimized with new constraints on the Pmap region. Initial and optimized treatment plans were compared using the T-test for independent variables and the non-parametric Mann-Whitney U test otherwise, regarding both doses to OARs and PTV coverage (Planning Target Volume). Conformity and heterogeneity indexes were also compared. Results Dosimetric optimization was considered successful for 27 out of the 44 included patients (61.4%), meaning the dosimetric constraint on the Pmap region was achieved without compromising the PTV coverage (p = 0.61). Overall, optimization significantly decreased median DMean Pmap from 28.8Gy (IC95% 24.2-33.4) to 22.1Gy (IC95% 18.3-26.0). When focusing on the predicted risk of APT inputting the new dosimetric features, optimization significantly reduced the risk of APT (p < 0.0001) by reclassifying 43.2% (19/44) of the patients. Conclusion Our approach appears as both easily implementable on a daily basis and efficient at reducing the risk of APT. Regional radiosensitivity should be considered in usual lung dose constraints, opening the possibility of an easily implementable adaptive dosimetry planning. PO-1270 Reduction of the acute pulmonary toxicity with a VMAT adaptive radiotherapy in lung cancer patients V. Bourbonne 1,2 , F. Lucia 1,2 , V. Jaouen 2,3 , J. Bert 2 , M. Rehn 1 , O. Pradier 1,2 , D. Visvikis 2 , U. Schick 1,2

PO-1271 Redetermination Of Pd-L1 Expression After Chemo-Radiation In Locally Advanced Pd-L1 Negative NSCLC (RECAL TRIAL

S. Cozzi 1 , G. Timon 2 , E. Tagliavini 3 , R. Piro 4 , E. Borghi 5 , M. Tiseo 5 , C. Iotti 6 , P. ciammella 7

1 Azienda USL-IRCCS di Reggio Emilia, Reggio Emilia, 1. Radiation Therapy Department, Reggio Emilia, Italy; 2 Azienda USL- IRCCS di Reggio Emilia, Reggio Emilia, Italy., Radiation Therapy Department, Reggio Emilia, Italy; 3 Azienda USL/IRCCS di Reggio Emilia, Reggio Emilia, 2. Pathology Unit, Reggio Emilia, Italy; 4 Azienda Unità Sanitaria Locale-IRCCS di Reggio Emilia, 3. Department of Medical Specialties, Pneumology Unit, Reggio Emilia, Italy; 5 University Hospital of Parma, 4. Medical Oncology Unit, Parma, Italy; 6 Azienda USL-IRCCS di Reggio Emilia, 1. Radiation Therapy Department, Reggio Emilia, Italy; 7 Azienda USL-IRCCS di Reggio Emilia, Radiation Therapy Department, Reggio Emilia, Italy Purpose or Objective The PACIFIC trial showed that administration of maintenance Durvalumab in patients with stage III non small cell lung cancer (NSCLC) after chemo-radiotherapy (CRT) resulted in an increased overall survival: 42.9 versus 33,4 months at 5 years. However, in Europe, drug reimbursement is provided only in patients with PD-L1 expression higher than 1%. Recent