Universal Dosimetric Advantage of Adaptive Radiotherapy across Tumor Sizes and Locations In Lung SBRT for NSCLC
Abstract
Purpose
Inter-fractional anatomical changes in lung SBRT raise concerns about dosimetric accuracy and potential target under-dosage. Adaptive radiotherapy (ART) is a proposed strategy to correct these variations. This study aims to quantify the dosimetric degradation from these changes and assess the necessity of ART to restore plan quality.
Methods
This retrospective planning study retrospectively included 33 lung SBRT patients, each prescribed with 50Gy/5Fx radiation therapy on an emulator. For each patient, three plans were generated: 1) the original approved Reference plan (REF); 2) the non-adaptive Scheduled plan (SCH), created by recalculating the REF plan on the daily anatomy; and 3) the re-optimized Adaptive plan (ADP) on the same daily anatomy. Dosimetric parameters for planning target volume (PTV) coverage (PTV D99%, PTV D95%) and OARs were compared using the Wilcoxon signed-rank test. The ART benefit (ADP-SCH improvement) was correlated with tumor diameter and lobe location using the Wilcoxon rank-sum test.
Results
Compared to the REF plan, the SCH plan showed significant target coverage degradation. The median PTV D99 dropped from 48.0 Gy (REF) to 43.1 Gy (SCH) (p<0.001). ADP plans significantly recovered the median PTV D99 to 47.5 Gy (p<0.001 vs SCH). In terms of PTV D95, nine patients showed dose degradation over 5.0 Gy in SCH plans with a maximum of 14.5 Gy. This dosimetric benefit was necessary regardless of tumor characteristics. There was no significance between the PTV D99 improvement and tumor diameters or lobe locations.
Conclusion
Inter-fractional anatomical variations in lung SBRT lead to significant target under-dosage with standard IGRT. ART effectively and accurately restores target coverage to the intended level. The need for ART is ubiquitous and cannot be predicted by baseline tumor size or location. These findings suggest that a verification-based ART strategy is dosimetrically necessary to ensure treatment quality and safety in lung SBRT.