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

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiology

Background:

• Increasing patient dose concerns from CT scans necessitate exploring dose reduction strategies.
• Intravenous contrast-enhanced CT (contrast CT) offers potential for reducing scan frequency in treatment planning.

Purpose of the Study:

• To investigate the accuracy of dose calculations using contrast CT for treatment planning in lung, esophagus, and pancreas cancers.
• To compare dose-volume histograms (DVH) between contrast and non-contrast CT scans for planning target volumes (PTV) and organs-at-risk (OAR).

Main Methods:

• Treatment plans from 8 patients, simulated with and without contrast agent (CA), were analyzed.
• Intensity-modulated radiation therapy (IMRT)/3D plans were generated with inhomogeneity correction on non-contrast CT scans.
• Contrast CTs were fused to non-contrast studies, with contours and plans copied for comparison of DVHs.

Main Results:

• Ratios of PTV doses (contrast/non-contrast) for Dmax, D05, Dmean, Dmin, and D95 were within 1.0009±0.0013, 0.996±0.005, 0.990±0.005%, 0.970±0.030, and 0.984±0.009, respectively.
• Contrast CT slightly increased cord dose, with a Dmax ratio of 1.005±0.026, and two cases showing a ratio of 1.035.
• Differences in PTV D95 between contrast and non-contrast CT were generally within 2% when normalized to prescription dose.

Conclusions:

• Contrast CT can be clinically utilized for treatment planning in most cases, as PTV D95 differences are within acceptable limits.
• While generally accurate, careful attention to maximum cord dose is necessary when it approaches critical limits.
• Further evaluation may be warranted for specific OARs or complex treatment scenarios.