Program Information
A Feasibility Study of Independent Dose Verification for IMAT
T Kamima1*, R Takahashi1 , H Baba2 , M Yamashita3 , Y Sugawara4 , Y Sato1 , H Tachibana2 , (1) The Cancer Institute Hospital of JFCR, Koutou-ku, Tokyo,(2) The National Cancer Center Hospital East, Kashiwa-city, Chiba prefecture, (3) Kobe City Medical Center General Hospital, Kobe, Hyogo, (4) The National Center for Global Health and Medicine, Shinjuku-ku, Tokyo
Presentations
SU-E-T-32 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To assess the feasibility of the independent dose verification (Indp) for intensity modulated arc therapy (IMAT).
Methods:An independent dose calculation software program (Simple MU Analysis, Triangle Products, Japan) was used in this study, which can compute the radiological path length from the surface to the reference point for each control point using patient’s CT image dataset and the MLC aperture shape was simultaneously modeled in reference to the information of MLC from DICOM-RT plan. Dose calculation was performed using a modified Clarkson method considering MLC transmission and dosimetric leaf gap. In this study, a retrospective analysis was conducted in which IMAT plans from 120 patients of the two sites (prostate / head and neck) from four institutes were retrospectively analyzed to compare the Indp to the TPS using patient CT images. In addition, an ion-chamber measurement was performed to verify the accuracy of the TPS and the Indp in water-equivalent phantom.
Results:The agreements between the Indp and the TPS (mean±1SD) were -0.8±2.4% and -1.3±3.8% for the regions of prostate and head and neck, respectively. The measurement comparison showed similar results (-0.8±1.6% and 0.1±4.6% for prostate and head and neck). The variation was larger in the head and neck because the number of the segments was increased that the reference point was under the MLC and the modified Clarkson method cannot consider the smooth falloff of the leaf penumbra.
Conclusion:The independent verification program would be practical and effective for secondary check for IMAT with the sufficient accuracy in the measurement and CT-based calculation. The accuracy would be improved if considering the falloff of the leaf penumbra.
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