ESTRO 2022 - Abstract Book

S1048

Abstract book

ESTRO 2022

postoperative radiotherapy (PORT), which may also lower PNI values by suppressing immune function or by causing poor oral intake. Therefore, the purpose of this study was to investigate the relationship between PNI and survival and recurrence in patients with PORT. Materials and Methods We reviewed 97 Stage I-III NSCLC patients who underwent radical resection followed by PORT between January, 2004 and December, 2020 at our institution. We obtained PNI values for both pre-RT and post-RT (within 2 months after RT) by using the following formula: 10 x serum albumin (g/dL) + 0.005 X absolute lymphocyte count (cells/mm3). A cutoff value for PNI was determined by the time-dependent receiver operating characteristic curve (ROC). Pearson’s chi-square test was used to analyze the relationship between PNI and clinicopathologic parameters. The Kaplan-Meier method and the Log Rank test were performed to analyze overall survival (OS) and disease free survival (DFS). The Cox hazard model was applied for univariate and multivariate analysis. The median follow-up period was 52.8 month. Results The ROC curve of post-RT PNI exhibited higher area under the curve (AUC 0.68, cut-off: 47) than that of pre-RT PNI (AUC 0.55, cut-off: 51), and therefore the group was divided into high post-RT PNI (> 47) and low post-RT PNI ( ≤ 47). The 5-year OS was 41.8% in the low post-RT PNI group, compared to 66.2% in the high post-RT PNI group (p=0.018). The patients with both “low pre-RT and low post-RT PNI” had the worst survival outcome (5-yr OS : 31.1%). A multivariate analysis revealed that low post-RT PNI (HR 1.99, 95% CI 1.02-3.85, p=0.046) was one of the independent risk factors for mortality along with age and male sex. On the contrary, there was no significant difference in 5-year DFS between low and high post-RT PNI groups (13.2% vs 35.8%, p=0.23). Extranodal extension was the only significant factor for disease recurrence in a multivariate analysis (HR 2.12, 95% CI 1.21-4.14, p=0.008). Conclusion Low PNI status after PORT was significantly associated with unfavorable survival, but not the disease recurrence. This finding suggests that PNI can be used as a prognostic marker and any kind of intervention to maintain optimal PNI might improve survival. Further study with a larger population is required to validate the role of PNI in PORT setting. 1 Addenbrooke’s Hospital, Cambridge University Hospitals NHS Foundation Trust, Department of Clinical Oncology, Cambridge, United Kingdom; 2 Addenbrooke’s Hospital, Cambridge University Hospitals NHS Foundation Trust, Department of Medical Physics, Cambridge, United Kingdom Purpose or Objective Stereotactic ablative body radiotherapy (SABR) is a well-tolerated and effective treatment for patients with early-stage, non-small cell lung cancer (NSCLC) and standard treatment option for inoperable, non-ultra central tumours. There is increasing evidence supporting the use of SABR in operable patients too. We aimed to analyse clinical outcomes of patients treated with SABR and evaluate clinical, pathological and dosimetric factors that may influence outcomes. Materials and Methods Patients with early stage NSCLC treated with SABR between September 2012 and December 2016 were included in this study and followed up until January 2021. Patient demographics, tumour characteristics, radiotherapy planning dosimetric parameters, tumour recurrence and survival data were collected from electronic patient record systems. Descriptive statistics were performed and SPSS software was used for analysing clinical outcomes. Results n = 89. Median age 74 years (50 - 90), 49.5% of whom were male and 50.5% were female. Figure 1 summarises demographics of patients and tumour characteristics. 98.8% of patients had T1-2 tumours and 89.9% underwent SABR with 55Gy/5# fractionation. Dosimetric data analysis showed that the mean planning target volume (PTV) (cc) was 26.6 and the median was 21.5. In subgroup analysis, patients treated with 55Gy/5# and 60Gy/8#, the median PTV was 48.1cc and 23.08cc respectively. The PTV was larger in range and larger on average in those treated with 5 fractions (mean PTV 26.6cc) as opposed to those treated with 8 (mean PTV 25.3cc). The median values for R100, R50, and D2cm were 1.1 (0.21 - 1.63), 6 (4.1 - 13.9) and 31.4 Gy (range 21.1 - 45.18). The median mean lung dose and V20 were 3.3 Gy (1.68 Gy - 6.3 Gy) and 4.15 % (1.29 % - 8.7 %) respectively. The median PTV maximum and minimum doses (Gy) were 74.85 (19.19 - 83.8) and 47.8 (29.66 - 71.9) respectively. The PTV V90% and PTV V100% doses were 99.9 (30.27 - 100) and 95.015 (20.8 - 99.66). Patients had an overall median survival of 52.2 months (Kaplan-Meier survival analysis). Patients surviving to <1 year, 1 year, 2 years, 3 years, 4 years and 5 years and 6 years or more being 94.4%, 79.8%, 68.5%, 60.7%, 24.72% and 11.23% respectively. 9% of patients had local, 5.6% had regional and 14.6% had distant recurrent disease, 67% of patients had no recurrence. Of the variables examined, only the PTV volume and PTV minimum dose had an impact on overall survival on both uni- and multi-variate cox proportional analysis ( Figure 2 ). PO-1242 Clinical, pathological and dosimetric factors influencing outcomes in NSCLC treated with SABR M. Padden-Modi 1 , Y. Spivak 1 , I. Gleeson 2 , A. Robinson 2 , K. Thippu Jayaprakash 1