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Investigation of the Appropriate Dose Index for Evaluation of Patient Organ Doses in Cone-Beam Computed Tomography Scanning by Using a Monte Carlo Simulation

H Kamezawa

H Kamezawa1*, H Arimura2 , H Arakawa2 , N Kameda3 , (1) Teikyo University, Omuta, Fukuoka, (2) Kyushu University, Higashi-ku, Fukuoka, (3) Fujimoto General Hospital, Miyakonojo, Miyazaki


SU-I-GPD-I-4 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the appropriate dose index for evaluation of patient organ doses in cone-beam computed tomography (CBCT) scanning by using Monte Carlo (MC) simulation.

Methods: The appropriate dose index was investigated among six dose indices, i.e. CTDI_100, CTDI_IEC, CTDI_infinity and midpoint doses (f(0)_PMMA for a cylindrical PMMA phantom, f(0)_Ap for an anthropomorphic phantom and f(0)_Pat for a prostate cancer patient). The f(0)_Ap and f(0)_Pat were adopted to take into account the differences of the object sizes and materials among a cylindrical PMMA phantom, an anthropomorphic phantom and a prostate cancer patient. All dose indices were obtained based on the doses measured with a 100-mm ionization chamber and a cylindrical PMMA phantom. The CBCT system installed into a medical linear accelerator was modeled by using a MC simulation code (particle and heavy ion transport code system: PHITS). The organ dose for prostate (OD_prost) was obtained as a reference dose using the MC simulation to find the appropriate dose index at a center of a pelvic region in a CT voxel phantom, which was constructed from CT images of a prostate cancer patient.

Results: The error rates of the six dose indices to the OD_prost (reference) were 91% for the CTDI_100, 80% for the CTDI_IEC, 67% for the CTDI_infinity, 64% for the f(0)_PMMA, 37% for the f(0)_Ap and 7% for the f(0)_Pat.

Conclusion: Our results suggests that the appropriate dose index for evaluation of the patient organ doses from CBCT scan was the midpoint dose f(0)_Pat, which showed the smallest error to the reference dose obtained by the MC simulation.

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