P2.05-037 Higher Radiation Dose is Still Promising in Patients with Complete Response to 50 Gy of Early Thoracic Radiotherapy with Chemotherapy?: Topic: RT Techniques

Abstract

For limited stage small cell lung cancer (LSCLC), early thoracic radiotherapy (TRT) with chemotherapy and radiation dose more than 60Gy has been suggested as standard therapy. We aim to evaluate the survival outcomes in LSCLC patients with complete response (CR) to 50 Gy of TRT with chemotherapy. One hundred and fifteen patients with LSCLC who completed the TRT from August 2005 to March 2014 were reviewed retrospectively. We evaluated the age, gender, smoking status, AJCC stage, PET parameters, tumor volume, dose and timing of TRT, duration of treatment, and prophylactic cranial irradiation (PCI) as a prognostic variables. Gross tumor volume (GTV) was defined as the post-chemotherapy tumor volume at the time of the first TRT planning and the pre-chemotherapy involved lymph nodes. Clinical target volume (CTV) was defined as GTV with minimum 7mm margin including the first echelon drainage lymph node station. At the time of 50 Gy of TRT, follow up chest CT was performed to all patient and only patients who showed non-CR received 10 Gy or more radiation. Dose of TRT was median 50 Gy (range, 42 to 65 Gy). Ninety-seven (84.3%) patients received concurrent chemoradiotherapy (CRT) and PCI was performed in all eligible patients. For all patients, median survival was 27.8 months. Two & 3-year OS were 60.7% and 38.58%, respectively. Sixty-five patients (56.5%) showed the complete response (CR) and fifty patients (43.5%) showed non-CR. There was correlation between tumor response to 50Gy of TRT and the ratio of GTV to CTV (p=0.008) or AJCC stage (p=0.036). With univariate analysis, AJCC stage (p<0.001), ratio of GTV to CTV (p = 0.005), tumor response to 50Gy of TRT (p = 0.004), the duration from the start date of induction chemotherapy to the end of TRT (SER, p = 0.003), and PCI (p = 0.035) were statistically significant predictor of OS. Multivariate Cox regression demonstrated that AJCC stage (p<0.001) and SER (p = 0.007) only were significant. In patients with SER <80days & CR to 50Gy TRT, median survival was not yet reached until now. LSCLC patients who showed CR to 50 Gy of TRT and completed TRT within 80days represented the outstanding survival outcomes. Based on these results, we need the further study evaluating whether dose escalation more than 50 Gy is promising for survival improvement in patients with CR at the time of 50 Gy of early TRT and chemotherapy.