The Planning Target Volume Change During SBRT Lung Treatment for Adaptive Radiation Therapy
Presentations
PO-GePV-M-113 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To study the Planning Target Volume (PTV) change during SBRT lung treatment for adaptive radiation therapy.
Methods: Thirteen SBRT lung patients were retrospectively studied. All patients’ data, including planning CT, contour, treatment plan and setup CBCT for each treatment were sent to Ethos adaptive treatment planning system (Varian, Palo Alto) for analysis. Patients were prescribed 60Gy in 3-5 fractions covering 95% of PTV. The PTV changes during treatment were tracked by Ethos adaptive contouring based on the Cone Beam CT during patient set up. The PTV change was calculated as a percentage of its volume on the planning CT.
Results: The initial PTV for all patients ranged from 11.58 cm³ to 295.15 cm³ with medium size 33.27 cm³. The average maximum PTV change during treatment of all 13 patients is 11.9% and ranged from 6.9% to 17.2%. The maximum PTV change does not depend on the PTV size. Although the trends of PTV change are patient specific, the treated PTV is smaller than the initial PTV in most fractions.
Conclusion: PTV is changing during each treatment for SBRT lung delivery. Adaptive radiation therapy may provide better OAR sparing while keeping the PTV coverage at each treatment.
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