Dose comparison between CTDI and the AAPM Report No. 111 methodology in adult, adolescent, and child head phantom

Celina L. Li; Yogesh Thakur; Nancy L. Ford

doi:10.1117/12.2254611

9 March 2017 Dose comparison between CTDI and the AAPM Report No. 111 methodology in adult, adolescent, and child head phantom

Celina L. Li, Yogesh Thakur, Nancy L. Ford

Author Affiliations +

Proceedings Volume 10132, Medical Imaging 2017: Physics of Medical Imaging; 101320T (2017) https://doi.org/10.1117/12.2254611
Event: SPIE Medical Imaging, 2017, Orlando, Florida, United States

Abstract

The standard computed tomography dose index (CTDI) metric tends to underestimate scatter radiation in cone beam computed tomography (CBCT) acquisition; therefore, the American Association of Physicists in Medicine (AAPM) Task Group 111 proposed a new dosimetry methodology to measure equilibrium dose at the center of a phantom (z = 0) using a 2-cm thimble ionization chamber. In this study, we implement the CTDI and the AAPM method with a thimble chamber on adult, adolescent, and child head phantoms using the Toshiba Aquilion One CBCT and compare the results to the CTDI measured with a 10-cm pencil chamber. Following the AAPM protocol, the normalized (100 mAs) equilibrium doses (D_eq) computed using dose measurements taken in the central hole of the phantom (D_eq,c), the peripheral hole of the phantom, (D_eq,p), and by the CTDI_w equation (D_eq,w) are 20.13 ± 0.19, 21.53 ± 0.48, and 20.93 ± 0.40 mGy for adult; 21.55 ± 0.40, 21.14 ± 0.43, and 21.08 ± 0.45 mGy for adolescent; and 24.58 ± 0.40, 24.92 ± 0.85, and 24.77 ± 0.72 mGy for child, respectively. The CTDI_w, which measured 17.70, 19.86, and 22.43 mGy for adult, adolescent and child respectively, is about 10% lower than their corresponding D_eq’s. The extended AAPM method proposed by Deman et al., which estimates the dose profile along the rotational axis (z axis), has demonstrated consistency between theoretical and experimental results for all phantoms. With the introduction of the child and the adolescent head phantoms, we not only have emphasized the practical aspects including relative convenience of the CTDI method and accuracy of the AAPM method, but also proposed a method to approximate D_eq for different sized patients.

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Celina L. Li, Yogesh Thakur, and Nancy L. Ford "Dose comparison between CTDI and the AAPM Report No. 111 methodology in adult, adolescent, and child head phantom", Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 101320T (9 March 2017); https://doi.org/10.1117/12.2254611

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KEYWORDS

Head

Ionization

Computed tomography

Medicine

Polymethylmethacrylate

Scanners

Medical imaging

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