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The Influence of Optimizing Pediatric CT Simulator Protocols On the Treatment Dose Calculation in Radiotherapy

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Y Zhang

Y zhang1*, J Deng2 , J Zhang1 , Q Hu1 , J Tie1 , H Wu1 , (1) Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Radiotherapy, Peking University Cancer Hospital & Institute, Beijing, China (2) Department of Therapeutic Radiology, Yale University, New Haven, CT, USA


SU-E-J-113 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:To investigate the possibility of applying optimized scanning protocols for pediatric CT simulation by quantifying the dosimetric inaccuracy introduced by using a fixed HU to density conversion.

Methods:The images of a CIRS electron density reference phantom (Model 062) were acquired by a Siemens CT simulator (Sensation Open) using the following settings of tube voltage and beam current: 120 kV/190mA (the reference protocol used to calibrate CT for our treatment planning system (TPS)); Fixed 190mA combined with all available kV: 80, 100, and 140; fixed 120 kV and various current from 37 to 444 mA (scanner extremes) with interval of 30 mA. To avoid the HU uncertainty of point sampling in the various inserts of known electron densities, the mean CT numbers of the central cylindrical volume were calculated using DICOMan software. The doses per 100 MU to the reference point (SAD=100cm, Depth=10cm, Field=10X10cm, 6MV photon beam) in a virtual cubic phantom (30X30X30cm) were calculated using Eclipse TPS (calculation model: AcurosXB_11031) by assigning the CT numbers to HU of typical materials acquired by various protocols.

Results:For the inserts of densities less than muscle, CT number fluctuations of all protocols were within the tolerance of 10 HU as accepted by AAPM-TG66. For more condensed materials, fixed kV yielded stable HU with any mA combination where largest disparities were found in 1750mg/cc insert: HUreference=1801(106.6cGy), HUminimum=1799 (106.6cGy, errordose=0.00%), HUmaximum=1815 (106.8cGy, errordose=0.19%). Yet greater disagreements were observed with increasing density when kV was modified: HUminimum=1646 (104.5cGy, errordose=-1.97%), HUmaximum=2487 (116.4cGy, errordose=9.19%) in 1750mg/cc insert.

Conclusion:Without affecting treatment dose calculation, personalized mA optimization of CT simulator can be conducted by fixing kV for a better cost-effectiveness of imaging dose and quality especially for children. Unless recalibrated, kV should be constant for all anatomical sites if diagnostic CT scanner is used as a simulator.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Capital Medical Development Scientific Research Fund of China.

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