ESTRO 2020 Abstract Book

S224 ESTRO 2020

different protocols. Patients treated with cisplatin (n=122) had a better OS as opposed to carboplatin (n=28)

associated with better PFS but on multivariate analysis only R100 was statistically significant.

(p=0,003). Conclusion

Vinorelbin in combination with cisplatin either as a single dose of 80mg/m² per cycle or daily doses of 20mg/m² (5 days per cycle) for concurrent chemoradiation show similar efficacy in this patient cohort. Patients treated with carboplatin had a significant worse survival. This may be due to the selection of the drug due to restriction in normal tissue function, which may also cause an impaired prognosis. PD-0414 Correlating dosimetry with the outcomes - A analysis of UK’s largest cohort of lung SABR patients. A. Saha 1 , M. Beasley 1 , N. Hatton 1 , K. Franks 1 , P. Jain 1 , M. Teo 1 , K. Clarke 1 , P. Dickinson 1 , P. Murray 1 , J. Lilley 2 1 St. James Institute of Oncology- Leeds Teaching Hospitals- NHS trust., Clinical Oncology, Leeds, United Kingdom ; 2 St. James Institute of Oncology- Leeds Teaching Hospitals- NHS trust., Medical Physics, Leeds, United Kingdom Purpose or Objective SABR is an established treatment option for early stage medically inoperable peripheral lung cancer. A recent study have shown that tight conformity of radiotherapy plans might worsen loco-regional control and can predict distant metastases. The aim of the study is to report local control (LC), progression free survival (PFS), overall survival (OS) and dosimetry of early stage peripheral lung cancer patients treated with SABR and to try to explore any dosimetric predictors of outcome. Material and Methods 1266 patients treated in our institute (May 2009 - August 2018) were included. Electronic medical records were reviewed for baseline characteristics, treatment details and outcomes. Dosimetric data was extracted from XIO and Monaco software. Patients were treated according to the UK SABR consortium guidelines. Kaplan Meier analysis with log rank test was used for survival analysis. Univariate and multivariate cox regression model was used for exploring the correlation between the dosimetric variables and outcomes, using IBM SPSS statistics version 21 software. Results Median age was 75 years with 47.4% male. Median follow up was 56 months. Median OS was 36 months with 1, 2 and 5 years OS rates of 84.2%, 64.5%,31.5%, respectively. Median for LC and PFS wasn’t reached. 1,2 and 5 years LC rates were 98.2%,95.1%,92.5%, respectively.1,2 and 5 years PFS rates were 87.4%, 78.4%,72.5%, respectively. PTV volume, dose to 99% volume of PTV (D99) and R50 were significantly associated with OS in univariate analysis. On multivariate analysis PTV volume and minimum dose to PTV (DPTV min) were significantly associated with OS (Table 1). D99 of >53 Gy and R100 of >1.1 was significant associated with better OS(Table 2).Nothing was associated with LC on univariate analysis but on multivariate analysis, dose fractionation were found to be associated with LC. R100 of >1.1 was associated with better local control. PTV volume, mean lung dose (MLD) , V20 , V12.5 and dose fractionation were significantly associated with PFS on univariate analysis. On multivariate analysis PTV volume and dose fractionation were significantly associated with PFS. 60Gy in 8 fractions regimen was better compared to 50Gy in 8 fractions regimen in terms of PFS but not for OS or local control. PTV volume ≤30 cc, R100 >1.1, R50 >6 and MLD ≤4Gy was

Conclusion SABR treatment resulted in promising LC, PFS and OS in early stage lung cancer patients considering the fact these are elderly patients with multiple comorbidies. Increasing PTV volume can significantly worsen the outcomes. R100 of > 1.1 resulted in better outcomes, indicating that tight conformality with steep dose gradient may worsen outcomes. Greater R50 improved OS and PFS. 8 fraction regimen is inferior to 3 fraction regimen in terms of LC. Smaller fraction regimen is significantly better than larger fraction regimen in terms of PFS but there is no significant difference in OS.