ESTRO 2023 - Abstract Book

S1071

Digital Posters

ESTRO 2023

Stereotactic body radiation therapy (SBRT) provides an alternative therapy option in non-operable early-stage non-small cell lung cancer (ES-NSCLC) patients. We aimed to assess clinical parameters correlating with SBRT efficacy and toxicity. Materials and Methods ES-NSCLC Patients with T1-2N0M0 treated with SBRT (median dose 60Gy/8 fractions) between 2005 and 2019 were included in this analysis. Clinical and pathological status, and treatment characteristics were assessed and correlated with overall survival (OS), local control (LC), regional control (RC; not including LC), distant control (DC), radiation-induced pneumonitis (RP) and radiation-induced lung fibrosis (RILF). Three resampling (iterations = 1000) feature selection methods, including a univariate analysis under Cox proportional hazards model (P<0.1), a random forest-based method and lasso regression, were applied to evaluate the predictive power of the considered features. Multivariate Cox proportional hazards models were then trained for each outcome with the features identified as significant by the feature selection pipeline and assessed based on a 5-fold, respectively 10-fold cross-validated concordance index (C-I). Results 101 patients were found eligible. Median follow-up time was 18 months (range 1-71 months). Median biologically effective dose (BED 10), D50 Gy and V20 of the total lung was 105 Gy, 1.75 Gy and 9%. Reported 1-year and 3-year OS, LC, RC, DC, were 95%, 92%, 98%, 93%, and 87%, 84%, 94%, 85%, respectively. Overall, pneumonitis rate was 6% and lung fibrosis rate 18%. Univariate analysis (UV) showed that squamous cell (SCC) histology was associated with shorter OS (HR=3.84, p<0.05) and a trend towards reduced tumor control (p<0.1); additional factors linked to poorer tumor control were lower mean dose (ipsilateral lung) and female gender (p<0.1). In multivariate analysis (MV) of OS, tumor histology, D50 Gy (total lung) and FEV1 were identified (C-I: 0.70). For LC (MV), V20 Gy, gender, and tumor location (C-I: 0.61), and for RC (MV) additionally, tumor histology (C-I: 0.61) were identified. DC (MV) parameters were V20 Gy, tumor histology, and D5 Gy at the planning target volume (C-I: 0.60). UV risk factors for RILF were lower lobe tumor localization, as well as BED 10 at the planning target volume periphery (p<0.1). No generalizable multivariate model could be derived for RP. For RILF (MV), tumor location (lower lobe and central vs peripheral) and prescribed biologically effective dose were identified (C-I: 0.74). Conclusion SBRT treatment produced excellent loco-regional control rates and consequently OS in ES-NSCLC, favorably in patients with non-squamous histology. Risk of RILF is enhanced for tumors located in the lower lobe. Purpose or Objective Stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC) was started at our hospital in 2006. In the last 10 years, we have changed the dose prescription method (from isocenter prescription to D95 prescription) and the dose calculation algorithm (from pencil beam convolution without inhomogeneity correction algorithm to anisotropic analysis algorithm). We investigated the local control rate (LC) of stage I NSCLC treated with SBRT in 2017-2018, and compared to that in patients treated with SBRT in 2006-2012. Materials and Methods In our hospital, 48 NSCLC tumors were received SBRT in 2017-2018 and 172 NSCLC tumors received SBRT in 2006-2012. The principle prescribed doses were 42 Gy in 4 fractions for D95 in 2017-2018, and 48 Gy in 4 fractions for isocenter in 2006 2012. Results The median follow-up was 43 months for the 2017-2018 cases and 31 months for the 2006-2012 cases. The LC was 93.2% at 2 years and 90.4% at 3 years in the 2017-2018 cases and 89.9% at 2 years and 87.9% at 3 years in the 2006-2012 cases. There were no statistically significant differences between LC of 2017-2018 cases and that of 2006-2012 cases (log-rank test, p=0.3768). Conclusion There was no significant difference in LC between recent cases and early cases in our hospital. From our results, there seemed to be little effect of dose prescription methods, calculation algorithm, and institutional skill in SBRT technique. C. Nicolas-Boluda 1 , G. Alberca 1 , C. Cigarral 1 , E. Tenllado 2 , J. Hernández 2 , K. Aylas 3 , A. Noé 4 , Á. Matías 1 , L.A. Pérez Romasanta 1 1 Complejo Asistencial Universitario de Salamanca, Radiation Oncology, Salamanca, Spain; 2 Complejo Asistencial Universitario de Salamanca, Radiophysics, Salamanca, Spain; 3 Hospital Universitario de Cáceres, Radiation Oncology, Cáceres, Spain; 4 Cork University Hospital, Radiation Oncology, Cork, Ireland Purpose or Objective To determine the response and prognosis of patients with early stage medically inoperable biopsy-proven non-small cell lung carcinoma (NSCLC) and suspected primary malignant lesions treated exclusively with stereotactic body radiation therapy (SBRT). PO-1337 Recent local control rates of stage I NSCLC treated with stereotactic body radiotherapy Y. Hamamoto 1 , H. Kanzaki 1 , K. Nagasaki 1 , K. Makita 1 1 National Hospital Organization Shikoku Cancer Center, Radiation Oncology, Matsuyama, Japan PO-1338 SBRT for early-stage lung cancer: outcomes from biopsy-proven and unproven lung lesions

Materials and Methods