Investigation of a practical patient dose index for assessment of patient organ dose from cone-beam computed tomography in radiation therapy using a Monte Carlo simulation

The purpose of this study was to investigate a practical patient dose index for assessing the patient organ dose from a cone-beam computed tomography (CBCT) scan by comparing eight dose indices, i.e. CTDI₁₀₀, CTDI_IEC, CTDI_∞, midpoint doses f(0)_PMMA for a cylindrical polymethyl methacrylate (PMMA) phantom, f(0)_Ap for an anthropomorphic phantom and f(0)_Pat for a prostate cancer patient, as well as the conventional size specific dose estimations (SSDE_conv) and modified SSDE (SSDE_mod), with organ dose for the prostate (OD_prost) obtained via Monte Carlo (MC) simulation. The OD_prost was the reference dose used to find the practical dose index at the center of the pelvic region of a prostate cancer patient. The smallest error rate with respect to the OD_prost of 19.3 mGy (reference) among eight dose indices was 5% for f(0)Pat. The practical patient dose index was the f(0)_Pat, which showed the smallest error with respect to the reference dose. (authors)