2180 - Quantitative Evaluation of Accumulated and Planned Dose Deviations in Gated and Non-Gated Lung SBRT Patients

S. Yang, K. Jingjing, Y. Chen, M. Hu, Y. Yu, N. Zhou, and Y. Xu; Department of Radiation Oncology, Shanghai Pulmonary Hospital, Tongji University School of Medicine, Shanghai, China

Purpose/Objective(s): This study aimed to investigate the dosimetric deviations in stereotactic body radiation therapy (SBRT) between gated and non-gated radiotherapy techniques and to analyze the impact of tumor location, target volume, and tumor motion range on dose distribution accuracy. Materials/

Methods: A retrospective analysis of 60 non-small cell lung cancer (NSCLC) patients treated with either gated or non-gated SBRT was performed. The planned dose distributions were computed using 4D-CT simulations to account for breathing motion, while the actual dose delivered was obtained by accumulating each fraction dose with synthetic CT (sCT) methods. The deviations between the planned and actual accumulated doses were statistically analyzed for both groups. The impact of tumor location and volume on dose distribution was also assessed.
Results: Gated SBRT showed significantly higher dosimetric precision, with median relative changes in ITV_D_min, ITV_D_mean, and ITV_D_max of -0.44%, -0.33%, and -0.49%, respectively. Non-gated SBRT presented larger median relative reductions in these parameters (p<0.001 for D_min). In gated SBRT, PTV_D_min and PTV_D_mean variances were significantly lower (p = 0.014 and p = 0.007, respectively), and prescribed dose volumes (PTV_V_90%PD and PTV_V_100%PD) were more accurately delivered (p = 0.006 and p = 0.029, respectively). Tumor location and volume analyses revealed that gated SBRTs dosimetric benefits were particularly pronounced in smaller ITVs and in the left lower-lung central region (LLCR) (p<0.001 for ITV_D_min in small volumes).
Conclusion: Gated SBRT offers enhanced dosimetric accuracy over non-gated SBRT, affirming its potential for improved therapeutic outcomes in NSCLC patients. These results advocate for the preferential use of gated SBRT in cases requiring precise dose delivery due to tumor movement or smaller target volumes.