Pediatric patient-specific organ dose estimations for chest and abdominopelvic CT examinations are possible with knowledge of patient size and CTDI vol, according to a study published in the February 2014 issue of Radiology.
In order to improve dose recording/monitoring and optimize CT protocols, accurate patient dose estimates must be acquired. However, patient dose can’t be characterized by a single metric thanks to the body’s multitude of organs with varying radiosensitivity. “As an alternative, patient dose is often indexed in terms of dose indicators such as the volume CT dose index (CTDI vol) and the size-specific dose estimate (SSDE),” wrote the study’s lead author, Xiaoyu Tian, of Duke University in Durham, N.C., and colleagues.
The current reference standard for organ dose estimation is Monte Carlo computation, which can be difficult due to the challenges associated with modeling patient anatomy. Tian et al estimated organ dose from pediatric chest and abdominopelvic CT studies and evaluated the dependences of organ dose coefficients on patient size and scanner models.
Using a validated Monte Carlo program, the researchers performed simulations in 42 pediatric patient models. Organ doses for each patient model were estimated for chest and abdominopelvic examinations. These estimations were normalized with CTDI vol, and the relationships between the normalized organ dose coefficients and average patient diameters were analyzed across the two scanner models used.
The CTDI vol-normalized organ dose coefficients exhibited a strong exponential relationship with the average patient diameter. The average percentage differences between the two scanner models used was typically within ten percent. Differences between the scanners were larger, ranging from 3-32 percent, for distributed organs and organs on the periphery of the image coverage. The difference ratios for all organs in the chest and abdominopelvic studies were within one percent.
“Such information may aid in improved dose recording and monitoring, in dose estimation for multiple CT examination protocols across different CT scanners, in CT protocol optimization, and in the evaluation of dose profiles within a practice,” wrote Tian and colleagues.
The study was limited by several factors, including the use of scanner-averaged coefficients that may not be applicable to organs outside of the image coverage. The authors suggest developing scanner-specific conversion coefficients for these organs in the future.