SU-E-T-545: Dose Comparison between Intravenous Contrast-Enhanced CT and Non Contrast CT in Treatment Planning

With increasing concern for patient dose from CT scan, we are trying to reduce CT scan and use intravenous contrast-enhanced CT (contrast CT) in treatment planning. This study is to investigate dose calculation accuracy using contrast CT in treatment planning for lung, esophagus and pancreas cancer.

We analyzed treatment plans for 8 patients for whom CT simulation was performed both with and without intravenous contrast agent (CA) (non-contrast CT). IMRT/3D plans were generated with inhomogeneity correction on the non-contrast CT scan. Contrast CTs were fused to the non-contrast studies and all contours and plans were copied to the contrast CT scans. For each patient, we analyzed dose-volume histograms (DVH) for planning volumes (PTV) and the organs-at-risk (OAR), comparing the doses generated on non-contrast CT scans with those generated on contrast CT scans.

Maximum doses ratio Dmax(contrast)/Dmax (non-contrast) in PTVs was 1.0009±0.0013. The ratio of D05 (contrast)/D05 (non-contrast) was 0.996±0.005. The ratio of mean PTV dose Dmean(contrast)/Dmean(non-contrast) was 0.990±0.005%. The ratio of minimum dose Dmin(contrast)/Dmin(non-contrast) and D95(contrast)/D95(non-contrast) were 0.970±0.030 and 0.984±0.009, respectively. Contrast CT raised cord dose slightly. The ratio of cord Dmax was 1.005±0.026. However there were two cases the ratio of cord Dmax were 1.035.

The PTV D95 is usually normalized to prescription dose and the D95 differences between contrast and regular CT were within 2%. In most cases, the contrast CT could be used to treatment planning clinically. However more attention should be paid to maximum cord dose if it is already close to criteria limit.