ESTRO 2020 Abstract book

S583 ESTRO 2020

diagnostic threshold was tested using Receiver operating characteristics (ROC) curve. The chi square test was carried out to test the different risk factor groups against likelihood of grade ≥2 pneumonitis. Results Median age of the patients were 75 years with 52.6% female. Median follow up was 56 months. Sixty-five percent patients received 55Gy in 5-fraction regimen. 43.5% patients had ECOG performance status (PS) of 2 and 16.2% had PS of 3. Median Charlson comorbidity index was 6 (range 2-11). Median SUV max of tumour was 6.5. Only 31.8% had confirmed histological diagnosis. Median tumour size was 20mm (range 4mm-63mm). Median planning target volume (PTV) was 30.3 cc. Median values of R100, R50 and D2cm were 1.1, 5.6, 32.8Gy. Median value of mean lung dose(MLD), V20 and V12.5 were 3.9Gy, 5 %and 9.3%. 85(6.7%) patients developed symptomatic RP (grade ≥2) with only 5(0.4%) developing grade 3 RP. 5% of patients developed rib fracture but only 28% of these were symptomatic. On univariate analysis lower lobe tumour location, larger tumour size, PTV, MLD, V20 and V12.5 were significantly associated with grade ≥2 RP. On multivariate analysis only higher MLD was associated with grade ≥2 pneumonitis (Table 1). ROC curve analysis showed optimal diagnostic threshold for tumour size, PTV, MLD, V20 and V12.5 (Figure 1); are 22.5mm (AUC- 0.565), 27.15cc (AUC-0.58), 3.7Gy (AUC- 0.633), 4.6% (AUC-0.597), 9.5% (AUC-0.616).The incidence of ≥grade 2 RP were significantly higher for values higher than the ROC threshold.

1 Chonnam National University Hwasun Hospital, Radiation Oncology, Hwasun-gun, Korea Republic of

Purpose or Objective Radiation-induced lymphopenia is common during concurrent chemoradiation (CCRT) and is associated with poor outcome. So, we aim to identify the dosimetric parameters in association with lymphopenia. Material and Methods 201 patients with locally advanced stage III NSCLC who received CCRT 60Gy in 30 fractions from 2010 and 2017 were included in this study. All patients received concurrent weekly chemotherapy consisting of paclitaxel first (50 mg/m2 intravenously over 1 hour) and cisplatin (20 mg/m2 intravenously over 1 hour). The median number of cycles of chemotherapy was 5 (range, 1–6). Absolute lymphocyte count (ALC) and absolute neutrophil counts (ANC) were analyzed at pre- and during CCRT. ALC ratio was defined as the ratio of nadir ALC count during CCRT to ALC count pre- CCRT. Pre-CCRT neutrophil–lymphocyte ratio (NLR) was defined as dividing the ANC by the ALC. The associations of the clinical and dosimetric parameters with lymphopenia and treatment outcomes were analyzed. Results Stage IIIA and stage IIIB were 143 (71.1%) and 58 (28.9%), respectively. One hundred and fifty (74.5%) were squamous cell carcinoma with age range of 40 to 75 years (median, 66). The overall survival (OS) and progression- free survival (PFS) of all patients were median 28 months and 12 months, respectively. Age, gross tumor volume (GTV) and lung V30 >16% were significant factors affecting OS on multivariate analysis (Table 1). Pre–CCRT NLR, ALC ratio during CCRT, and mean lung dose (MLD) were associated with PFS on multivariate analysis. Pre–CCRT NLR, ALC ratio, and MLD also were associated with an increased risk of distant metastases. In stepwise multivariate linear regression analysis, GTV and Heart V10 were significantly associated with lymphocyte nadir as a continuous variable. The median PFS stratified by ALC ratio >0.21 and ALC ratio ≤0.21 was 13 months and 8 months, respectively. On univariate logistic analysis, many variables showed to be significantly associated with the development of ALC ratio ≤0.21, including GTV, MLD, Lung V5, Lung V10, Lung V20, Lung V30, mean heart dose, heart V5, heart V10, heart V20, heart V30, and heart V40. The multivariate logistic regression analysis revealed that GTV ( p = 0.008) and heart V20 ( p = 0.001) were the most significant predictors of ALC ratio ≤0.21.

Conclusion SABR treatment resulted in very low rate of grade 3 pneumonitis. Lower lobe tumour location, larger tumour size, PTV, mean lung dose, V20 and V12.5 were found to be significant predictors of symptomatic radiation pneumonitis. PO-1008 Predictive dosimetric parameters of lymphopenia in stage III NSCLC patients with chemoradiation I.J. Cho 1 , Y. Kim 1 , S. Ahn 1 , W. Chung 1 , T. Nam 1 , M.S. Yoon 1 , J. Jeong 1 , J. Song 1 , S. Cho 1

Conclusion This study shows that RT-induced lymphopenia is associated with worse patient outcomes in locally advanced NSCLC patients undergoing CCRT. GTV and heart V20 were significantly associated with ALC reduction ratio.