Hua Li PhD, Presenter: Nothing to Disclose

Beth Bottani, Abstract Co-Author: Nothing to Disclose

Todd DeWees, Abstract Co-Author: Nothing to Disclose

Daniel A. Low PhD, Abstract Co-Author: Scientific Advisory Board, ViewRay, Inc

Jeff M. Michalski MD, Abstract Co-Author: Nothing to Disclose

Sasa Mutic MS, Abstract Co-Author: Stockholder, ViewRay, Inc Stockholder, Radialogica, LLC

Jeffrey D. Bradley MD, Abstract Co-Author: Nothing to Disclose

Cliff Grant Robinson MD, Abstract Co-Author: Nothing to Disclose

Purpose/Objective:To investigate the effects of using IV contrast CT scans on IMRT treatment planning for lung cancer patients and its clinical significance.Materials/Methods:Eight patients with lung cancer (1 small cell, 7 non-small cell) scheduled to receive IMRT consented to acquisition of simulation CT scans with and without IV contrast. The non-contrast scan was deemed the primary dataset while the contrast scan was used for contouring. Clinical treatment plans optimized on the non-contrast scans were re-computed on contrast scans and compared on PTV and organs at risk (OAR) dose coverage, and γ pass rate.Results:Median prescription dose to the PTV was 200 cGy (range, 150-267 cGy) over 30 fractions (range, 15-33). Planning was accomplished using a median of 7 beams (range, 6-13) calculated with a heterogeneity correction dose algorithm. Using non-contrast scan as reference, the median absolute/relative differences in mean, maximum, and minimum dose to the PTV was -6.5 cGy (range, -49.6 to +57.6 cGy) / -0.09% (range, -1.04% to +1.54%), 3.2 cGy (range, -54.5 to +308.1 cGy) / 0.62% (range, -1.21% to +4.06%), and -19.7 cGy (range, -164.5 to +143.4 cGy) / -0.50% (-3.55% to +2.65%). Regarding OARs, the median absolute/relative differences of maximum dose to heart was -5.5 cGy (range, -71.3 to +51.2 cGy) / -0.32% (range, -4.80 to +0.81%), to esophagus was -33.2 cGy (range, -109.4 to +168.3 cGy) / -0.89% (range, -1.62 to +2.66%), and to spinal cord was -4.9 cGy(range, -108.1 to +15.4 cGy) / -0.46% (range, -2.60 to +0.49%).Subjectively, the regions with absolute dose differences higher than 3% of the prescription dose are small and typically located at patient periphery and/or at the edge of beams, at where larger calculation uncertainty and co-registration uncertainty occurs between the non-contrast and contrast scans. The median γ pass rate was 0.9981 (range, 0.9654 to 0.9999) with 3% absolute dose difference / 3 mm distance-to-agreement (DTA) criteria. One case had a lower γ pass rate 0.9654 with 3% / 3 mm criteria because respiratory motion caused liver position offset between the non-contrast and contrast scans. Clinically, the compared dose areas with γ pass rate > 0.95 are considered equivalent when using 3% / 3 mm criteria. Overall, all evaluated cases were found to be clinically equivalent.T-tests indicated that the γ pass rate is not significantly less than 99%. Signed rank tests indicated that no statistical significant different of the dose distributions calculated on either non-contrast or contrast scans.Conclusions:PTV and OARs dose differences between non-contrast and contrast scans appear to be minimal for lung cancer patients undergoing IMRT. Using IV contrast scans as the primary simulation dataset could increase treatment planning efficiency and accuracy by avoiding unnecessary scans, manually region overridden, and errors caused by image registration.

Li, H, Bottani, B, DeWees, T, Low, D, Michalski, J, Mutic, S, Bradley, J, Robinson, C, Prospective Study Evaluating the Use of IV Contrast on IMRT Treatment Planning for Lung Cancer.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13041297.html