Determination of dose-area product from panoramic radiography using a pencil ionization chamber: normalized data for the estimation of patient effective and organ doses.

Abstract

The aims of the present study were (a) to investigate the potential of pencil ionization chamber to be used for the determination of dose-width product (DWP) and dose-area product (DAP) from panoramic radiographic exposures and (b) to provide data normalized to DAP for the determination of patient effective and gonadal dose from panoramic radiography performed in any laboratory. A pencil ionization chamber commonly used to measure CT dose index (CTDI) in CT scanners was employed to determine DWP for various combinations of panoramic exposure settings at the beam exit slit of a Cranex Tome panoramic x-ray unit (Soredex, Helsinki, Finland). DWP values were also measured using an array of thermoluminescence dosimeters. Reproducibility of the DWP measurement was tested. The effect of milliamperage and kilovoltage of panoramic exposures on DWP was investigated. DAP was estimated using the value of DWP measured using the pencil ionization chamber and the beam exit slit length measured using dosimetric film attached on the beam exit slit. A Rando anthropomorphic phantom appropriately loaded with thermoluminescent dosimeters (TLDs) was used to obtain organ dose and effective dose values from panoramic radiography. Reproducibility of DWP determination using the proposed method was better than 1.5%. DWP was found to be linearly related to milliamperage (r>0.999, p<0.001) and to kilovoltage raised in a power ranging from 2.18 to 2.55. DWP measured using the pencil chamber was found to be up to 11% higher than the corresponding values determined using TLD array. The panoramic exposure obtained with settings appropriate for the typical adult patient was found to result in 0.008 mSv patient effective dose, 0.0002 mGy gonadal dose, and 11.3 cGy cm2 DAP. The use of a pencil ionization chamber is proposed for the determination of DWP and DAP from panoramic radiographic exposures. Normalized data over DAP were provided for the determination of patient effective and gonadal dose from panoramic radiography.