Robustness of Tumor Control Against Intrafraction Patient Motion in Lung Stereotactic Body Radiation Therapy

IntroductionIn stereotactic body radiation therapy (SBRT), patient motion during treatment may significantly impact the tumor control probability.In this study, we performed an analysis of patient outcomes to determine the clinical robustness of our lung SBRT protocols against patient motion and to assess the overall efficacy of our unique treatment delivery technique. Methods & Materials78 patients treated for 85 primary lung tumors or lung metastases with SBRT were included.An abdominal compression belt was used for respiratory motion management.Prescription doses were 50-70 Gy delivered in 5 fractions.Our standard planning target volume (PTV) expansion was 5.0 mm.Imageguided positional corrections were performed halfway through treatment.Intrafraction shifts were recorded for analysis.Kaplan-Meier analysis was performed to determine the 2-and 3-year local control (LC) and overall survival (OS).Toxicities were evaluated using Common Terminology Criteria for Adverse Events (CTCAE) version 6.0. ResultsThe median follow-up duration was 25 months (IQR: 13-40 months).Course-averaged intrafraction patient motion ranged from 1.2-8.2mm (median 3.5mm, IQR: 2.5-4.0 mm).The 2-and 3year LC [95% CI] were 97.6% [83.9-99.7%]and 94.0% [77.3-98.5%],respectively.2-and 3-year OS were 77.3% [65.8-87.8%]and 69.6% [56.8-79.3%].The two local recurrences were observed at 22 and 31 months post-SBRT.They were associated with the 33 rd largest and the smallest average repositioning shifts in the study.No adverse events (AE) of grade 3 were observed over the study interval. ConclusionsThe excellent local control rates observed irrespective of patient positioning uncertainty were demonstrative of the clinical robustness of our SBRT workflow and may support future studies investigating PTV margin reduction.High efficacy and low toxicity rates support implementation of this workflow in clinics developing SBRT programs.Similar study designs may be used to assess alternative SBRT workflows.