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KMID : 0357520200430040265
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Journal of Radiological Science and Technology
2020 Volume.43 No. 4 p.265 ~ p.272
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Evaluation of Dose Volume and Radiobiological Indices by the Dose Calculation Grid Size in Nasopharyngeal Cancer VMAT
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Kang Dong-Jin
Jung Jae-Yong
Shin Young-Joo
Min Jung-Whan
Shim Jae-Goo
Park So-Hyun
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Abstract
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The purpose of this study was to investigate the dose-volume indices and radiobiological indices according to the change in dose calculation grid size during the planning of nasopharyngeal cancer VMAT treatment. After performing the VMAT treatment plan using the 3.0 ㎜ dose calculation grid size, dose calculation from 1.0 ㎜ to 5.0 ㎜ was performed repeatedly to obtain a dose volume histogram. The dose volume index and radiobiological index were evaluated using the obtained dose volume histogram. The smaller the dose calculation grid size, the smaller the mean dose for CTV and the larger the mean dose for PTV. For OAR of spinal cord, brain stem, lens and parotid gland, the mean dose did not show a significant difference according to the change in dose calculation grid size. The smaller the grid size, the higher the conformity of the dose distribution as the CI of the PTV increases. The CI and HI showed the best results at 3.0 ㎜. The smaller the dose calculation grid size, the higher the TCP of the PTV. The smaller the dose calculation grid size, the lower the NTCP of lens and parotid. As a result, when performing the nasopharynx cancer VMAT plan, it was found that the dose calculation grid size should be determined in consideration of dose volume index, radiobiological index, and dose calculation time. According to the results of various experiments, it was determined that it is desirable to apply a grid size of 2.0 ? 3.0 ㎜.
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KEYWORD
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Dose calculation grid size, Conformity index (CI), Homogeneity index (HI), Tumor control probability (TCP), Normal tissue complication probability (NTCP)
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