Interval From Simulation Imaging to Treatment Delivery in SABR of Lung Lesions: How Long is Too Long for the Lung?

Abstract

Purpose: The purpose of this study was to evaluate the effect of delay between planning computed tomography (CT) used as a basis for treatment planning and the start of treatment (delay planning treatment [DPT]), on local control (LC) for lung lesions treated by SABR. Methods and Materials: We pooled 2 databases from 2 monocentric retrospective analysis previously published and added planning CT and positron emission tomography (PET)–CT dates. We analyzed LC outcomes based on DPT and reviewed all available cofounding factors among demographic data and treatment parameters. Results: A total of 210 patients with 257 lung lesions treated with SABR were evaluated. The median DPT was 14 days. Initial analysis revealed a discrepancy in LC as a function of DPT and a cutoff delay of 24 days (21 days for PET-CT almost systematically done 3 days after planning CT) was determined according to the Youden method. Cox model was applied to several predictors of local recurrence–free survival (LRFS). Univariate analysis showed LRFS decreasing significantly related to DPT ≥24 days (P = .0063), gross tumor volume, and clinical target volume (P = .0001 and P = .0022), but also with the presence of >1 lesion treated with the same planning CT (P = .024). LRFS increased significantly with higher biological effective dose (P < .0001). On multivariate analysis, LRFS remained significantly lower for lesions with DPT ≥24 days (hazard ratio, 2.113; 95% confidence interval, 1.097-4.795; P = .027). Conclusions: DPT to SABR treatment delivery for lung lesions appears to reduce local control. Timing from imaging acquisition to treatment delivery should be systematically reported and tested in future studies. Our experience suggests that the time from planning imaging to treatment should be <21 days.