Toxicity Related to Radiotherapy Dose and Targeting Strategy: A Pooled Analysis of Cooperative Group Trials of Combined Modality Therapy for Locally Advanced Non-Small Cell Lung Cancer

Objective: Concurrent chemoradiotherapy (CRT) was the standard treatment for locally advanced NSCLC (LA-NSCLC). This study was performed to examine thoracic radiotherapy (TRT) parameters and their impact on adverse events (AEs).

Methods: We collected individual patient data from 3600 patients with LA-NSCLC who participated in 16 cooperative group trials of concurrent CRT. The TRT parameters examined included field design strategy (elective nodal irradiation [ENI] versus involved-field [IF] TRT [IF-TRT]) and TRT dose (60 Gy versus ≥60 Gy). The primary end point of this analysis was the occurrence of AEs. ORs for AEs were calculated with univariable and multivariable logistic models.

Results: TRT doses ranged from 60 to 74 Gy. ENI was not associated with more grade 3 or higher AEs than IF-TRT was (multivariable OR = 0.77, 95% confidence interval [CI]: 0.543-1.102, p = 0.1545). Doses higher than 60 Gy (high-dose TRT) were associated with significantly more grade 3 or higher AEs (multivariable OR = 1.82, 95% CI: 1.501-2.203, p < 0.0001). In contrast, ENI was associated with significantly more grade 4 or higher AEs (multivariable OR = 1.33, 95% CI: 1.035-1.709, p = 0.0258). Doses higher than 60 Gy were also associated with more grade 4 or higher AEs (multivariate OR = 1.42, 95% CI: 1.191-1.700, p = 0.0001). Grade 5 AEs plus treatment-related deaths were more frequent with higher-dose TRT (p = 0.0012) but not ENI (p = 0.099).

Conclusions: For patients with LA-NSCLC treated with concurrent CRT, IF-TRT was not associated with the overall risk of grade 3 or higher AEs but was associated with significantly fewer grade 4 or higher AEs than ENI TRT. This is likely the result of irradiation of a lesser amount of adjacent critical normal tissue. Higher TRT doses were associated significantly with grade 3 or higher and grade 4 or higher AEs. On the basis of these findings and our prior report on survival, CRT using IF-TRT and 60 Gy (conventionally fractionated) were associated with more favorable patient survival and less toxicity than was the use of ENI or higher radiotherapy doses.