Program Information
CT-Based Independent Dose Verification for RapidArc Plan as a Secondary Check
H Tachibana1*, T Kamima2 , R Takahashi2 , H Baba1 , (1) The National Cancer Center Hospital East, Kashiwa, Chiba, (2) The Cancer Institute Hospital of JFCR, Koto, Tokyo
Presentations
SU-E-T-505 Sunday 3:00PM - 6:00PM Room: Exhibit HallPurpose: To design and develop a CT-based independent dose verification for the RapidArc plan and also to show the effectiveness of inhomogeneous correction in the secondary check for the plan.
Methods: To compute the radiological path from the body surface to the reference point and equivalent field sizes from the multiple MLC aperture shapes in the RapidArc MLC sequences independently, DICOM files of CT image, structure and RapidArc plan were imported to our in-house software. The radiological path was computed using a three-dimensional CT arrays for each segment. The multiple MLC aperture shapes were used to compute tissue maximum ratio and phantom scatter factor using the Clarkson-method. In this study, two RapidArc plans for oropharynx cancer were used to compare the doses in CT-based calculation and water-equivalent phantom calculation using the contoured body structure to the dose in a treatment planning system (TPS).
Results: The comparison in the one plan shows good agreement in both of the calculation (within 1%). However, in the other case, the CT-based calculation shows better agreement compared to the water-equivalent phantom calculation (CT-based: -2.8% vs. Water-based: -3.8%). Because there were multiple structures along the multiple beam paths and the radiological path length in the CT-based calculation and the path in the water-homogenous phantom calculation were comparatively different.
Conclusion: RapidArc treatments are performed in any sites (from head, chest, abdomen to pelvis), which includes inhomogeneous media. Therefore, a more reliable CT-based calculation may be used as a secondary check for the independent verification.
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