Quantitative evaluation of accumulated and planned dose deviations in patients undergoing gated and non-gated lung stereotactic body radiation therapy patients: a retrospective analysis.

Background: Stereotactic body radiation therapy (SBRT) is crucial for treating early-stage inoperable non-small cell lung cancer (NSCLC) due to its precision and high-dose delivery. This study aimed to investigate the dosimetric deviations in gated (GR) versus non-gated radiotherapy (NGR), analyzing the impact of tumor location, target volume, and tumor motion range on dose distribution accuracy.

Methods: Sixty patients treated with either gated (n=30) or non-gated (n=30) SBRT for early-stage NSCLC were retrospectively analyzed. The planned dose distributions were determined using four-dimensional computed tomography simulations to account for breathing motion, while the actual dose delivered was determined by accumulating each fractional dose with synthetic computed tomography (sCT) methods. The deviations between the planned and actual accumulated doses were statistically analyzed for both groups. The effects of tumor location and volume on dose distribution were also assessed.

Results: Gated SBRT showed significantly higher dosimetric precision with median relative changes in the minimum dose within the ITV (ITV_D_min), mean dose received by the ITV (ITV_D_mean), and maximum dose within the ITV (ITV_D_max) of -0.44%, -0.33%, and -0.49%, respectively. Non-gated SBRT presented with larger median relative changes in these parameters (P<0.001 for the ITV_D_min). In gated SBRT, the PTV_D_min (minimum dose within the PTV) and PTV_D_mean (mean dose received over the entire PTV) differences were significantly lower favoring gated SBRT (P=0.01 and P=0.007, respectively), and for the prescribed dose volumes, the volume of PTV receiving 90% prescription dose (PTV_V_90%PD) and the volume of PTV receiving 100% prescription dose (PTV_V_100%PD) were more accurately delivered, also favoring gated SBRT (P=0.006 and P=0.03, respectively). The tumor location and volume analyses demonstrated that the dosimetric benefits of gated SBRT were particularly significant in the smaller internal target volumes (ITVs) and in the left lower central lung region (P<0.001 for the ITV_D_min in small volumes).

Conclusions: Gated SBRT affords dosimetric accuracy compared to non-gated SBRT, and thus could improve the therapeutic outcomes of NSCLC patients. These results should advocate for the preferential use of gated SBRT in cases requiring precise dose delivery due to large respiratory motion or small target volumes.