(Tuesday, 7/16/2019) 7:30 AM - 9:30 AM
Room: 221AB
Purpose: Proton radiography (pRG) of mobile tumors could improve a target localization and provide a water equivalent path length (WEPL) verification, facilitating accurate treatments with reduced side effects. A technique for tumor motion pRG is empirically explored based on time dependent energy resolved dose functions (ERDF) reconstructed from multiple motion cycles using a single X-ray flat panel imager.
Methods: The range of the proton beam used in imaging was modulated by a modulator wheel rotating at a rate of 0.5 Hz, and ERDFs for deriving WEPL values were acquired with a PaxScan 4030CB panel. A CIRS respiratory motion phantom was used and the measured WEPL values were compared to those derived from computed tomography (CT) as reference, evaluating the accuracy. In order to acquire adequate data points to rebuild EDRFs for every respiration phase, multiple respiration cycles were recorded and segmented. A series of different phantom configurations were applied to create various respiratory patterns.
Results: The reconstructed pRG images show expected contrast in WEPL among different tissue materials such as ribs, lungs, and soft tissues. The tumor motion was divided into 10 phases and the motion artifacts were found negligible. Differences between CT ray tracing and pRG derived WEPL images are about 1 ± 10 mm, and main discrepancies appear in high WEPL contrast areas, such as the spinal area.
Conclusion: Sorting-based pRG reconstruction of mobile targets has shown the possibility to provide accurate WEPL estimates for real patients. Future study of this method combined with CT reconstruction may further improve the accuracy of proton therapy of moving tumors.
Funding Support, Disclosures, and Conflict of Interest: Liyan Zhang is awarded a scholarship by China Scholarship Council to pursue this study, covering the international airfare and the living stipend.
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