Dosimetry analysis of panoramic-imaging devices in different-sized phantoms

The aim of this study is to measure the radiographic dose in adult, adolescent, and child head-sized PMMA phantoms for three panoramic-imaging devices: the panoramic mode on two CBCT machines (Carestream 9300 and i-CAT NG) and the Planmeca ProMax 2D. A SEDENTEXCT dose index adult phantom and custom-built adolescent and pediatric PMMA dosimetry phantoms were used. Panoramic radiographs were performed using a Planmeca ProMax 2D and the panoramic mode on a Carestream 9300 CBCT and an i-CAT NG using the protocols used clinically. Point dose measurements were performed at the center, around the periphery and on the surface of each phantom using a thimble ionization chamber. Five repeat measurements were taken at each location. For each machine, single-factor ANOVA was conducted to determine dose differences between protocols in each phantom, as well as determine the differences in absorbed dose when the same protocol was used for different-sized phantoms. For any individual phantom, using protocols with lower kVp, mA, or acquisition times resulted in statistically significant dose savings, as expected. When the same protocol was used for different-sized phantoms, the smaller phantom had a higher radiation dose due to less attenuation of x-rays by the smaller phantom and differences in the positioning of the ion chamber relative to the focal trough. The panoramic-mode on the CBCT machines produce images suitable for clinical use with similar dose levels to the stand-alone panoramic device. Significant dose savings may result by selecting age- and size- appropriate protocols for pediatric patients, but a wider range of protocols for children and adolescents may be beneficial.