ESTRO 2020 Abstract Book

S531 ESTRO 2020

(p=0.0001), or symptoms of dysphagia (p=0,01) and/or chest pain (p=0.001), as well as those who did not receive surgical treatment (p=0.024) (there were no differences between patients undergoing RT with concomitant or sequential CT schedule). Conclusion Patients over 75 years of age tend to receive more conservative treatments (less surgery and less concomitant RT and CT). The surgical modality improved OS and therefore, it should be carefully considered on case-by- case basis, regardless of patient age. A history of comorbidities and poor baseline QOL according to the EORTC QLQc30 and LC-13 (low physical functioning, marked dysphagia, and chest pain) are predictive of shorter OS. Measuring these parameters before treatment may help us to define a population of frail patients with poorer prognosis to facilitate decision making in clinical practice PO-0995 Impact of the dose outside the PTV on distant recurrence in coplanar and non-coplanar lung SBRT V.J. Heng 1 , A. Diamant 1 , A. Chatterjee 1 , S. Faria 2 , H. Bahig 3 , E. Filion 3 , R. Doucet 3 , I. El Naqa 4 , J. Seuntjens 1 1 McGill University, Medical Physics Unit, Montreal, Canada ; 2 McGill University Health Centre, Radiation Oncology, Montreal, Canada ; 3 Centre Hospitalier de l'Université de Montréal, Radiation Oncology, Montreal, Canada ; 4 University of Michigan, Radiation Oncology, Ann Arbor, USA Purpose or Objective A previous study had suggested that the dose proximally outside the PTV could have an impact on the incidence of distant metastasis (DM) after conventional SBRT in stage I NSCLC patients. In a 30 mm isotropic shell extending from the PTV margin, it was found that patients receiving a mean dose larger than a threshold dose of 21 Gy, in EQD2 (α/β=10Gy), had a significantly superior DM-free survival. In the present study, we investigate this observation in non-coplanar SBRT delivery (CyberKnife) and compare it with the previous conventional SBRT cohort. Material and Methods This study included 422 stage I NSCLC patients from 2 institutions who received SBRT: 217 treated conventionally, either with VMAT or 3D conformal radiation therapy (CRT) and 205 with CyberKnife. The dose behavior outside the PTV of both sub-cohorts were compared by analyzing the mean dose in continuous shells extending 1, 2, 3, ..., 100 mm from the PTV. The DM-free survival of patients treated with CyberKnife was compared to the sub-cohort of patients receiving less than the 21 Gy threshold dose (VMAT/CRT_{<21Gy}) with a Kaplan-Meier analysis. To determine the impact of exceeding the 21 Gy threshold dose on distant recurrences, a multivariate Cox proportional hazards model was fitted to the combined cohort (n = 422) using DM incidence as the endpoint while adjusting for age, tumor staging, histology, coplanarity of the treatment and other clinical factors. Results The shell-averaged dose fall-off beyond the PTV was found to be significantly slower in CyberKnife plans than in conventional SBRT plans. In a 30 mm shell around the PTV, the mean dose delivered with CyberKnife (38.1 Gy) is significantly larger than with VMAT/CRT (22.8 Gy, p<10^{- 8}). For 95% of CyberKnife plans, this region receives a mean dose larger than the 21 Gy threshold dose discovered in our previous study. In contrast, this occurs for only 75% of VMAT/CRT plans. The DM-free survival of the entire CyberKnife cohort is superior to that of the 25% of VMAT/CRT patients receiving less than the threshold dose (VMAT/CRT_{<21Gy}), with a hazard ratio of 5.3 (CI: 3.0 - 9.3, p<10^{-8}). The 2 year DM-free survival rates were 87% and 44% for the entire CyberKnife and the VMAT/CRT_{<21Gy} cohorts respectively. A multivariate analysis of the combined cohort with DM incidence survival

as the endpoint found that exceeding the threshold dose was associated with a significantly lower risk of DM with a hazard ratio of 0.29 (CI: 0.14 - 0.58, p<10^{−3}) when adjusted for other clinical factors.

Conclusion In standard-of-care lung CyberKnife treatments, dose distributions that aid distant control are achieved 95% of the time. Although similar doses could be physically achieved by coplanar deliveries, current prescription practices result in worse DM outcomes for 25% of conventional lung SBRT patients. Our study suggests that adding an additional prescription parameter to a 30 mm shell outside the PTV could reduce distant recurrence rates in conventional SBRT patients. PO-0996 Early mortality in stage III NSCLC after radical non-surgical therapy following ESMO guidelines M. Ronden-Kianoush 1 , I.F. Remmerts de Vries 1 , I. Bahce 2 , P.F. De Haan 1 , M.A. Tiemessen 3 , F.O.B. Spoelstra 1 , V.D.M. Van Diepen 4 , C.J.A. Haasbeek 1 , S. Tarasevych 5 , H.J.M.A. Daniels 2 , M.R. Dahele 1 , S.M. Hashemi 2 , A. Becker 2 , J.D. Veltman 6 , L.M.M. Crombag 6 , S. Senan 1 , W.F.A.R. Verbakel 1 1 Amsterdam UMC - VUmc, Radiation Oncology, Amsterdam, The Netherlands ; 2 Amsterdam UMC - VUmc, Pulmonary Diseases, Amsterdam, The Netherlands ; 3 Dijklander Ziekenhuis Hoorn, Pulmonary Diseases, Hoorn, The Netherlands ; 4 Dijklander Ziekenhuis Purmerend, Pulmonary Diseases, Purmerend, The Netherlands ; 5 Zaans Medisch Centrum, Pulmonary Diseases, Zaandam, The Netherlands ; 6 Amsterdam UMC - AMC, Pulmonary Diseases, Amsterdam, The Netherlands Purpose or Objective The most recent European Society for Medical Oncology (ESMO) guideline recommends immunotherapy consolidation treatment using durvalumab for 12 months after completion of cCRT [ in press , Ann Oncol 2019]. Population studies of patients with stage III NSCLC report