Organ dose and inherent uncertainty in helical CT dosimetry due to quasiperiodic dose distributions

Winslow, J; Tien, Christopher Jason; Hintenlang, David E.

doi:10.1118/1.3590367

Cited by 12 publications

(8 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Correction method may be developed in future studies based on beam width, pitch factor, x-ray tube starting position, and the distance to the isocenter. 18 In conclusion, dose calculation using the approach to equilibrium function is unlimited to the center of the irradiated length. We formulated equations for calculating dose at any point on the axial line.…”

Section: Discussionmentioning

confidence: 99%

Equations for CT dose calculations on axial lines based on the principle of symmetry

2012

View full text Add to dashboard Cite

show abstract

Section: Discussionmentioning

confidence: 99%

Equations for CT dose calculations on axial lines based on the principle of symmetry

2012

View full text Add to dashboard Cite

show abstract

“…This is probably related to the geometrical exposure condition in volumetric MSCT and to the repeatability in the phantom position. As outlined in several studies [29,30], in helical multidetector computed tomography, there are significant variations of z-axis doses at phantom surfaces. Doses within those regions where direct primary beam exposure overlap occurs during helical scanning are greater and doses to regions where "gaps" in the primary beam exposure occur are lower.…”

Section: Discussionmentioning

confidence: 99%

Radiochromic films for dental CT dosimetry: A feasibility study

et al. 2014

View full text Add to dashboard Cite

Dental CT dose evaluations are commonly performed using thermoluminescent dosimeters (TLD) inside anthropomorphic phantoms. Radiochromic films with good sensitivity in the X-ray diagnostic field have recently been developed and are commercially available as GAFCHROMIC XR-QA. There are potential advantages in the use of radiochromic films such as a more comprehensive dosimetry thanks to the adjustable size of the film samples. The purpose of this study was to investigate the feasibility of using radiochromic films for dental CT dose evaluations. Film samples were cut with a width of 5mm and a length of 25 mm (strips), the same size as the Alderson Rando anthropomorphic phantom holes used in this study. Dental CT dose measurements were performed using simultaneously both TLD and radiochromic strips in the same phantom sites. Two equipment types were considered for dental CT examinations: a 16 slice CT and a cone beam CT. Organ equivalent doses were then obtained averaging the measurements from the sites of the same organ and effective doses were calculated using ICRP 103 weighting factors. The entire procedure was repeated four times for each CT in order to compare also the repeatability of the two dosimeter types. A linear correlation was found between the absorbed dose evaluated with radiochromic films and with TLD, with slopes of 0.930 and 0.944 (correlation r>0.99). The maximum difference between the two dosimeter's measurements was 25%, whereas the average difference was 7%. The measurement repeatability was comparable for the two dosimeters at cumulative doses above 15 mGy (estimated uncertainty at 1 sigma level of about 5%), whereas below this threshold radiochromic films show a greater dispersion of data, of about 10% at 1 sigma level. We obtained, using respectively Gafchromic and TLD measurements, effective dose values of 107 μSv and 117 μSv (i.e. difference of 8.6%) for the cone beam CT and of 523 μSv and 562 μSv (i.e. difference of 7%) for the multislice CT. This study demonstrates the feasibility of radiochromic films for dental CT dosimetry, pointing out a good agreement with the results obtained using TLD, with potential advantages and the chance of a more extensive dose investigation.

show abstract

“…The effects of ODM were studied using axial exams to avoid the confounding effects of helical start angle, which can significantly affect some organ doses. [10][11][12] Thirteen MOSFET dosimeters (mobile MOSFET Dosimetry System, Best Medical, Ottawa, Canada) were placed at tissue locations in the breast, lung, heart, eye lens, and brain regions to quantify radiation dose. Because the spine region was inaccessible for dosimeter placement, a dosimeter was placed in the posterior region of the lung in the closest insert to the spine region to estimate dose changes in the posterior "spine" region.…”

Section: A Experimental Methodsmentioning

confidence: 99%

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ‐based tube current modulation technique

Gandhi

Crotty²,

Stevens³

et al. 2015

Medical Physics

View full text Add to dashboard Cite

Purpose: This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison. Methods: Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated. Results: ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%-20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA. Conclusions: ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol.

show abstract

Organ dose and inherent uncertainty in helical CT dosimetry due to quasiperiodic dose distributions

Cited by 12 publications

References 12 publications

Equations for CT dose calculations on axial lines based on the principle of symmetry

Equations for CT dose calculations on axial lines based on the principle of symmetry

Radiochromic films for dental CT dosimetry: A feasibility study

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography organ‐based tube current modulation technique

Contact Info

Product

Resources

About