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Session: Multi-Disciplinary General ePoster Viewing [Return to Session]

CBCT-Based Plan Adaptation for Chest Wall Intensity Modulated Proton Therapy

W Smith*, Y Hao, B Sun, A Darafsheh, T Mazur, T Zhang, S Perkins, T Zhao, Washington University School of Medicine, St. Louis, MO


PO-GePV-M-81 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Cone-beam CT (CBCT) is an important imaging modality for precise positioning and monitoring gross anatomical changes. However, CBCT is not suitable for dose calculation in intensity-modulated proton therapy (IMPT), largely limited by the lack of accuracy in Hounsfield units. This work demonstrated a new workflow that utilizes CBCT for fractional dose verification as well as adaptation for chest wall IMPT.

Methods: A small cohort of four chest wall patients (three ipsilateral and one bilateral) were included in this study. All had one simulation helical CT and at least one setup CBCT. Three had verification helical CTs at some points in their radiotherapy course. A synthetic CBCT was created by deforming the simulation helical CT to a setup CBCT in RayStation. Structures contoured on the simulation CT were also propagated to the synthetic CBCT through the same chain of deformable imaging registration. Dose to the targets and normal organs were reported and compared among the simulation helical CT, the synthetic CBCT, and verification helical CT.

Results: V95% of PTV and V5Gy heart were consistent among planning CT, synthetic CBCT, and verification CT with less than 3% and 1% variation, respectively. Except for one who suffered from significant swelling of tumor stroma. In the latter case, the synthetic CBCT was able to predict the PTV re-contoured independently and the dose within 1% on a replanning helical CT triggered by the synthetic CBCT.

Conclusion: This work supports the assertion that CBCT imaging can be used as an early warning system capable of detecting anatomy changes that warrants adaptive planning. The synthetic CBCT we developed in this study could be a powerful tool for fractional dose verification and quick plan adaptation in IMPT.



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