The impact of overall treatment time on outcomes in radiation therapy for non-small cell lung cancer

Abstract

Purpose: A retrospective study was carried out to evaluate the impact of overall treatment time (OTT) on the results of radiation therapy for non-small cell lung cancer (NSCLC). Materials and methods: From Jan. 1990 to Dec. 1996, 256 patients with stages I–IIIb NSCLC entered this analysis. All patients received definitive radiotherapy. Biologically effective dose (BED) was used to standardize the irradiation effects. The correlation between OTT and local progression-free survival was analyzed by linear-regression and Cox proportional hazard models. The prognostic variables for survival and distant metastasis were also briefly studied. Results: OTT had been shortened in 64 patients because of an accelerated hyperfractionated irradiation, while OTT was prolonged in 114 patients due to interruptions of irradiation courses. The main causes of interruption were machine breakdown or delayed preparations of cerrobend block for boost fields (55%), holidays (11%) and treatment toxicity and side-effects (34%). Patients treated with prolonged OTT (>45 days) had significant poorer local progression-free survival than whom with OTT of ≤45 days, 1, 3 and 5 year actuarial local progression-free survivals being 49, 17 and 15% for the former, and 74, 35 and 25% for the latter, respectively ( P<0.001). BED-T that contained the factor of OTT correlated directly to local controls, which implied that BED-T represented radiobiological effects accurately, in other words, OTT had played a role in determining the radiobiological effects. Linear-regression on 103 cases treated with BED of 80–85 Gy 10 showed that 3 year local progression-free survival decreased by 9% per week with prolongation of OTT, or vice versa it increased by 9% per week with shortening OTT in an OTT range of 30–76 days. Cox multivariate analyses confirmed that OTT was an independent prognostic factor for local controls. Conclusion: OTT may have played an important role in determining local controls in radiotherapy for NSCLC. One should always keep in mind to make the OTT as short as possible, provided the patients can tolerate it, and to reduce irradiation interruptions for whatever reasons to a minimum.