Purpose: To investigate the impact of exclusively using intravenous (IV) contrast x-ray computed tomography (CT) scans on lung cancer intensity-modulated radiation therapy (IMRT) treatment planning.
Methods: Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive IMRT consented to acquisition of simulation CT scans with and without IV contrast. Clinical treatment plans optimized on the noncontrast scans were recomputed on contrast scans and dose coverage was compared, along with the γ passing rates.
Results: IV contrast enhanced scans provided better target and critical structure conspicuity than the noncontrast scans. Using noncontrast scan as a reference, the median absolute/relative differences in mean, maximum, and minimum doses to the planning target volume (PTV) were -4.5 cGy/-0.09%, 41.1 cGy/0.62%, and -19.7 cGy/-0.50%, respectively. Regarding organs-at-risk (OARs), the median absolute/relative differences of maximum dose to heart was -13.3 cGy/-0.32%, to esophagus was -63.4 cGy/-0.89%, and to spinal cord was -16.3 cGy/-0.46%. The median heart region of interest CT Hounsfield Unit (HU) number difference between noncontrast and contrast scans was 136.4 HU (range, 94.2-161.8 HU). Subjectively, the regions with absolute dose differences greater than 3% of the prescription dose were small and typically located at the patient periphery and/or at the beam edges. The median γ passing rate was 0.9981 (range, 0.9654-0.9999) using 3% absolute dose difference/3 mm distance-to-agreement criteria. Overall, all evaluated cases were found to be clinically equivalent.
Conclusions: PTV and OARs dose differences between noncontrast 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 overriding, and planning errors caused by nonperfect image registrations.