Comparison of two types of adult phantoms in terms of organ doses from diagnostic CT procedures

Abstract

The rapidly increasing number of diagnostic computed tomography (CT) procedures in the recent decades has spurred heightened concern over the potential risk to patients. Although an accurate organ dose assessment tool has now become highly desirable, existing software packages depend on stylized computational phantoms that were originally developed more than 40 years ago, exhibiting very large discrepancies when compared with phantoms that are anatomically realistic. However, past comparative studies did not focus on CT protocols for adult patients. This study was designed to quantitatively compare two types of phantoms, the stylized phantoms and a pair of recently developed RPI-adult male and adult female (RPI-AM and RPI-AF) phantoms, for various CT scanning protocols involving the chest, abdomen-pelvis and chest-abdomen-pelvis. Organ doses were based on Monte Carlo simulations using the MCNPX code and a detailed CT scanner model for the GE LightSpeed 16. Results are presented as ratios of organ doses from the stylized phantoms to those from the RPI phantoms. It is found that, for most organs contained in the scan volume, the ratios were within the range of 0.75-1.16. However, the stomach doses are significantly different and the ratio is found to be up to 1.86 in male phantoms and 2.29 in the female phantoms due to the anatomical differences between the two types of phantoms. Organs that lie near a scan boundary also exhibit a significant relative difference in organ doses between the two types of phantoms. This study concludes that, due to relatively low x-ray energies, CT doses are very sensitive to organ shape, size and position, and thus anatomically realistic phantoms should be used to avoid the dose uncertainties caused by the lack of anatomical realism. The new phantoms, such as the RPI-AM and AF phantoms that are designed using advanced surface meshes, are deformable and will make it possible to match the anatomy of a specific patient leading to further improvement in dose and risk assessments for patients undergoing CT examinations.

Extension of RPI-adult male and female computational phantoms to obese patients and a Monte Carlo study of the effect on CT imaging dose

“…The lack of realism offered by stylized phantoms may result in significant discrepancies in the calculated organ doses, ranging from a few per cent to over 100% under certain conditions when compared with image-based voxel phantoms (Chao et al 2001a, 2001b, Zankl et al 2002, Lee et al 2006). For instance, a recent CT dosimetry study by Liu et al (2010) reported a 25% difference between the calculated dose to stylized and voxel phantoms for organs within the scan range. Another major limitation of this study is that the adipose tissues were only positioned at the surface of the stylized phantom and did not account for fat located deep within the abdomen surrounding the internal organs.…”

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] The human body lying on a CT scanner table and helical fan beam x-ray generated from a CT scanner are fully simulated in the computer using the Monte Carlo method.…”

Estimation of Absorbed Dose Distribution in Different Organs during the CT Scan: Monte Carlo Study

“…Estımatıon of Absorbed Dose Dıstrıbutıon in Dıfferent Organs durıng the CT Scan: Monte Carlo Study most accurate, reliable, and versatile in accomplishing this task [1][2][3][4][5][6][7][8].…”