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Determination of the Optimum Gating Window in Lung Lesion Patients

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S Lally

S Lally*, D Pearson , University of Toledo, Toledo, OH


SU-I-GPD-T-514 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To examine the impact of gating window on dose distribution in respiratory gated radiotherapy of lung lesions and to determine the optimal gating window.

Methods: A sample of previous lung lesion patients was chosen to have treatment plans gated. 4DCT scans for these patients were then contoured in MIM using gating windows of 10%, 30%, 50%, 70%, 90%, and 100% of the full respiratory duty cycle. Contour structures were then exported into copies of the original plan in Pinnacle and beams were applied to mimic the original treatment. The plan targets were adjusted to fit the contours for the gated windows. Pinnacle calculated the treatments and dosage distributions for individual treatments. Efficiency was assessed by percentage decrease in target volume, percentage decrease in ipsilateral lung volume treated with greater than 20 Gy, and percentage decrease in ipsilateral lung mean dose.

Results: Percentage decrease in target volume becomes greater as the gating windows get smaller as expected. As for dose distribution, the volume of ipsilateral lung that receives 20 Gy and ipsilateral lung mean dose are used to quantify changes as the gating windows narrow. Results from both the ipsilateral lung dose and volume show greater percent decreases with each reduction in phase. While all patients followed this trend, various patients show greater decreases in percentage between different phases. When lesions were in proximity to the diaphragm it was also found that the volume of the liver that received greater than 15Gy decreased.

Conclusion: While some patients showed greater percentage decreases at different phases, no evidence indicated an optimal gating window.

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