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Evaluationof a Second-Check Dosimetry Verification System Based On MPPG 5.a Report

B Yang*,Z Wang ,T Pang,X Liu,T Dong,J Qiu,Fuquan Zhang, /Peking Union Medical College Hospital, Beijing, Beijing,


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To compare TPS dose calculated by Eclipse 13.6 (Varian Medical Systems) based on MPPG 5.a model to those computed with an independent verification system Mobius3D (M3D2.1, Mobius Medical Systems, LP).

Methods: A set of 6 MV clinical commissioning plans based on MPPG 5.a generated by Eclipse treatment planning systems were exported to Mobius3D. The DICOM-RT files who were sent to M3D includes RT CT images, RT structures, RT plan and RT dose. All 3D dose distributions were recalculated using a collapsed cone algorithm in M3D. Dose distributions were compared to those calculated by the TPS using a 3D gamma analysis with 3% global dose difference and 3 mm isodose point distance criteria.

Results: M3D plans showed different 3D gamma passing rates agreement of (99.34%±1.4%) and (66.59%±17.66%) relative to 3 cm -33cm field size and 33 cm -40cm field size for primary data respectively. All the other gamma passing rates included small field, Irregular field, asymmetric field, etc were more than 95%. For TG119 plans, the average gamma passing rates were 99.3%, 97.2%, 95.6% for VMAT, step-shoot IMRT and sliding-window IMRT respectively.

Conclusion: Based on MPPG 5.a, the verification system should be able to recalculate dose adequately as a verification tool of our TPS to find some system errors. we can rely on the system to accurately compute dose to a patient for simple and complex clinic cases. M3D has the potential to be used as a more extensive plan check tool and provide dosimetric data about the actual dose delivered to treatment volumes and OARs.


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