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SU‐E‐J‐113: The Influence of Optimizing Pediatric CT Simulator Protocols On the Treatment Dose Calculation in Radiotherapy
Author(s) -
Zhang Y,
Deng J,
Zhang J,
Hu Q,
Tie J,
Wu H
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888165
Subject(s) - imaging phantom , nuclear medicine , scanner , dosimetry , radiation treatment planning , physics , computer science , radiation therapy , biomedical engineering , optics , medicine , radiology
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=10×10cm, 6MV photon beam) in a virtual cubic phantom (30×30×30cm) 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: HU reference =1801(106.6cGy), HU minimum =1799 (106.6cGy, error dose =0.00%), HU maximum =1815 (106.8cGy, error dose =0.19%). Yet greater disagreements were observed with increasing density when kV was modified: HU minimum =1646 (104.5cGy, error dose =‐ 1.97%), HU maximum =2487 (116.4cGy, error dose =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. This work was partially supported by Capital Medical Development Scientific Research Fund of China.