Investigation of Eye Lens Dose Estimate based on AAPM Report 293 in Head Computed Tomography

Abstract

Background: Estimation of eye lens dose is important in head computed tomography (CT) examination since the eye lens is a sensitive organ to ionizing radiation. Objective:The purpose of this study is to compare estimations of eye lens dose in head CT examinations using local size-specific dose estimate (SSDE) based on size-conversion factors of the American Association of Physicists in Medicine (AAPM) Report No. 293 with those based on size-conversion factors of the AAPM Report No. 220. Material and Methods:This experimental study is conducted on a group of patients who had undergone nasopharyngeal CT examination. Due to the longitudinal (z-axis) dose fluctuation, the average global SSDE and average local SSDE (i.e. particular slices where the eyes are located) were investigated. All estimates were compared to the measurement results using thermo-luminescent dosimeters (TLDs). The estimated and measured doses were implemented for 14 patients undergoing nasopharyngeal CT examination. Results:It was found that the percentage differences of the volume CT dose index (CTDI vol ), average global SSDE based on AAPM No. 220 (SSDE o,g ), average local SSDE based on AAPM No. 220 (SSDE o,l ), average global SSDE based on AAPM No. 293 (SSDE n,g ) and average local SSDE based on AAPM No. 293 (SSDE n,l) against the measured TLD doses were 22.5, 21.7, 15.0, 9.3, and 2.1%, respectively. All comparisons between dose estimates and TLD measurements gave p-values less than 0.001, except for SSDE n,l (p-value = 0.566). Conclusion: SSDE based on AAPM ReportNo. 293 can be used to accurately estimate eye lens radiation doses by performing the calculations on a number of specific slices containing the eyes.

Applying the AAPM 293 report to estimate the absorbed dose during head computed tomography: using head circumference for rapid dose estimation

“…Values with P≤0.05 denoted statistical significance. The correlation interpretation (r) is as follows: |r|=1, perfect correlation; 0.8≤|r|<1, strong correlation; 0.5≤|r|<0.8, moderate correlation; 0.1≤|r|<0.5, weak correlation; and 0<|r|<0.1, the lowest correlation ( 16 ). Missing data were examined, and no patterns of missing data were identified.…”

“…While this and AAPM report 220 rely on similar calculation methods, the conversion factor ( f ) of report 293 is more accurate because its calculation method is based on head phantom experiments that consider different ages and the Monte Carlo simulation ( 15 ). A recent study also showed the average local SSDE calculated using size conversion factors from the AAPM report 293 has the highest accuracy for estimating eye lens radiation doses ( 16 ).…”

A system to investigate and adjust profile pattern of computed tomography dose index along the longitudinal-axis

“…With local CTDIvol, local SSDE values can be obtained. With the local SSDE value, the organ estimation becomes more accurate [22]. However, this approach alone is not sufficient to accurately estimate organ doses.…”