Analysis of optimal dose of thoracic radiotherapy for patients with extensive stage small cell lung cancer

Abstract

Objective To investigate the optimal dosage of thoracic radiotherapy in patients diagnosed with extensive stage small cell lung cancer (ES-SCLC). Methods Clinical data of ES-SCLC patients admitted to Tianjian Medical University Cancer Institute& Hospital between February 2010 and October 2015 were retrospectively analyzed. All patients received the first-line induction chemotherapy. Subsequently, 216 patients without progression after the first-line induction chemotherapy were apportioned to the thoracic radiotherapy (n=180) group and chemotherapy alone group (n=36). According to the distribution characteristics of the biological equivalent dose, all patients were assigned into the A (31.3-40.2 Gy, n=23), B (46.0-46.8 Gy, n=38), C (49.5-53.7 Gy, n=43) and D groups (55.1-60.6 Gy, n=76). For the subgroup analysis, the low (31.3-46.8 Gy, n=61) and high dose groups (49.5-60.6 Gy, n=119) were divided. Kaplan-Meier survival analysis was used for prognostic analysis. Cox’s regression model was conducted for multivariate prognostic analysis. Propensity score matching was utilized to control the confounding variables. Results The median overall survival of all patients was 13.2 months, and 8.3, 11.0, 15.8, 17.8 and 8.1 months for patients in the A, B, C, D and chemotherapy alone groups, respectively (all P=0.000). The median overall survival did not significantly differ between A and B/chemotherapy groups (P=0.172, P=0.495), and similar results were obtained between the C and D groups (P=0.624). The median overall survival in the B group was significantly longer than that in the chemotherapy alone group (P=0.020). Statistical significance was noted between C and D groups, and A and B groups (all P<0.05). The median progression-free survival for all patients was 8.7 months, and 6.5, 7.6, 11.8, 12.4 and 6.1 months in the A, B, C, D and chemotherapy alone groups, respectively (all P=0.000). The median progression-free survival did not significantly differ between A and B chemotherapy groups (P=0.588, P=0.668). The progression-free survival in the B group was slightly longer than that in the chemotherapy group without statistical significance (P=0.070). No statistical significance was observed between the C and D groups (P=0.627). Statistical significance was noted between C and D groups, and A and B groups (all P<0.02). Uni-and multi-variate analyses prompted that the number of metastatic lesions and dose of thoracic radiotherapy were the independent predictors of the overall survival and progression-free survival (both P<0.05). Concurrent chemoradiotherapy was the independent predictor of the overall survival (P=0.018). After the propensity score matching, the median overall survival and progression-free survival significantly differed between the low (n=50) and high dose groups (n=50)(10.9 vs. 17.5 months, P=0.045; 7.4 vs. 10.7 months, P=0.014). Conclusions A relatively high dose ranging from 49.5 to 53.7 Gy is recommended during thoracic radiotherapy for ES-SCLC patients. An excessively low dose (≤40.2 Gy) probably fails to prolong the survival time, and an extremely high dose (≥55.1 Gy) cannot enable the patients to obtain survival benefits. Key words: Lung neoplasms/radiotherapy; Prognosis