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Updated: May 2, 2026
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
Association Between Inter-Fraction Volume Changes and Patient Outcomes from Stereotactic Ablative Radiotherapy for
Wilson X Mai1, Melissa A Frick2, Scott Jackson1
1Department of Radiation Oncology, Stanford University, Stanford, CA.
Introduction:
The aim of this study was to investigate the clinical significance of inter-fraction volume changes during stereotactic ablative body radiotherapy (SABR) for early-stage NSCLC. The prevalence and impact on disease control remain poorly studied. This is the largest study examining the association between inter-fraction volume changes during lung SABR and clinical outcomes.
Patients And Methods:
121 NSCLC patients treated between April 2009 and July 2019 were included. Gross tumor volume (GTV) was calculated from planning-CT, and inter-fraction volumes from cone-beam CT images taken before treatment. Univariable and multivariable linear regression analyzed relationships between volumetric changes and baseline characteristics. Fine-Gray models assessed volume change associations with local, regional, and distant recurrence, considering death as a competing risk.
Results:
61.9% and 11.1% of tumors demonstrated a > 10% increase and decrease, respectively, in volume from the start to end of treatment. There was a negative correlation between initial tumor volume and inter-fraction volume increase on univariable analysis. Fine-Gray models showed no significant correlation between volume increase and local recurrence but found a negative association between volume increase and regional as well as distant recurrence.
Conclusions:
Notable radiographic volume changes occurred in over half of lung SABR patients. This phenomenon did not appear to adversely affect local control. Increased radiographic volume correlated with reduced regional and distant recurrence, possibly representing an immune effect. Our findings suggest volume changes are likely a consequence of acute inflammatory reactions rather than tumor growth, and modest PTV expansions may be sufficient for tumor coverage.
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