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P1.03 - Poster Session with Presenters Present (ID 455)
- Event: WCLC 2016
- Type: Poster Presenters Present
- Track: Radiology/Staging/Screening
- Presentations: 2
- Coordinates: 12/05/2016, 14:30 - 15:45, Hall B (Poster Area)
P1.03-021 - Initial Results from A Novel and Low Cost Method For Measuring CT Image Quality (ID 6317)
14:30 - 15:45 | Author(s): R.S. Avila
Accurate measurement of change in tumor size in Computed Tomography images is critical for lung nodule differential diagnosis. Standard CT scanner calibration phantoms and methods are routinely relied upon to ensure that image quality is generally sufficient for a wide range of imaging tasks. However, high precision medical imaging applications, such as RECIST and volumetric tumor change measurement, require much greater attention to maintaining consistently high image quality characteristics. A new ultra-low cost, and cloud based method has been developed to quickly assess the image quality of CT scanners and imaging protocols that provides both estimates of clinical task performance, such as lung tumor size measurement error rates, and fundamental image quality performance metrics. In addition, multiple large imaging organizations have made available lung cancer screening guidance documents indicating that CT slice thicknesses of <= 1.25 mm are either required or preferred.
To demonstrate the image quality site measurement capability a global challenge was launched during May and June of 2016 that allowed lung cancer screening sites to scan three rolls of 3M ¾ x 1000 inch Scotch Magic ™ Tape placed at increasing distances from iso-center on the CT table and using their standard low dose lung cancer screening protocol. Fully automated software detected the rolls of tape and estimated fundamental image quality parameters including CT linearity, 3D resolution, noise, and level of edge enhancement. In addition, metrics indicating the expected detection and volume change measurement performance for different diameter lung nodules were calculated.
A total of 27 clinical sites participated in the challenge and provided CT imaging data on over 54 CT scanners representing 18 scanner models made by Siemens, GE, Philips, and Toshiba. 17 out of 27 (63%) clinical sites provided data with <= 1.25mm DICOM specified slice thickness. However, only 19% of sites used <= 1.25mm slice thickness and a reconstruction kernel that avoided excessive smoothing and avoided high levels of edge enhancement.
A new rapid, ultra-low cost, and cloud based method for assessing the quality of CT imaging studies has revealed poor adherence to recommended protocols and large levels of variation in fundamental image quality properties. Utilization of these new tools has the potential to help correct image quality issues in clinical studies.
P1.03-052 - The Effect of Rounding on Rate of Positive Results on CT Screening for Lung Cancer (ID 6095)
14:30 - 15:45 | Author(s): R.S. Avila
Effective management of small pulmonary nodules to reduce frequency of false positives has been one of the most challenging issues to implementation of screening. Measurement of size is important as it determines whether a nodule is positive result and also whether growth has occurred. Lung-RADS v.1 guideline requires nodule measurement to be rounded to the nearest whole number, it is not specified whether individual length and width measures should also be rounded prior to rounding the diameter. An alternative approach is the one used in I-ELCAP where measurements were recorded to one decimal place. This study explored how rounding would affect the frequency of positive results both for baseline and annual rounds.
Using data collected from CT screenings of 21,136 I-ELCAP participants, we evaluated four different approaches for calculating the nodule diameter (D) based on measurements of the length (L) and width (W) listed below: 1) Measurement of L and W to one decimal place (x.x) and calculation of D without rounding; 2) rounding D to the nearest integer; 3) rounding the L and W measurements to the nearest integer before calculating D with no further rounding; and 4) rounding the calculated D determined by method 3 to the nearest integer. Threshold of positive results was 6.0 mm for baseline round and 4.0 mm for annual repeat rounds of screening. Frequency of positive results in the baseline and annual repeat rounds were compared.
For baseline screening using the current I-ELCAP definition (Method 1), the rate of positive results was 10.2%. Using method 2, 3 and 4, positive rates were 12.8%, 10.5% and 13.2%, respectively. Use of rounding would have increased the frequency of positive results by 25.7%, 3.0%, and 28.9%, respectively. Of 85,877 repeat screenings, the rate of positive results was 8.0% using method 1. Using method 2, 3 and 4, positive rates were 9.7%, 8.3% and 9.8%, respectively. Use of rounding would have increased the frequency of positive results on repeat screenings by 20.5%, 3.2%, and 22.3%, respectively.
Regardless of where the rounding occurred, it results in more nodules designated as positive. This effect is most pronounced when the rounding occurs in average diameter, and since frequency of nodules increases as size decreases, small nodules are therefore the most frequent cause for positive results and rounding can lead to large increases in positive rates.
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