Effects of Contrast Density Override on the Treatment Planning Workflow and Dose Calculations
Abstract
Purpose
Intravenous (IV) and oral contrast are often utilized during the CT simulation for radiation planning. Overriding contrast prior to planning and dose calculations is often a part of standard workflow. This project investigates the real-world impact the presence of contrast has on radiation planning dose calculations.
Methods
Twelve salvage prostate cancer plans that were calculated with Hounsfield Unit (HU) bladder contrast override to water density were reviewed. Plans were recalculated with no HU override and HU override applied to manually contoured contrast volume. Dose differences for each plan were documented for clinical target volume (CTV), planning target volume (PTV), and associated organs at risk (OARs). This same procedure was applied to 10 head and neck and 10 lung cancer patients with IV contrast at the time of simulation as well as for 10 rectal cancer patients who received oral contrast.
Results
For the prostate cohort, minimal dose increase was observed with HU contrast override compared to no contrast override, with mean mean-dose changes for CTV and PTV prostate of 9.85 cGy (0.21%) and 7.84 cGy (0.17%), respectively, and of lymph node 1.48 cGy (0.03%) and 1.73 cGy (0.04%), respectively. Prostate CTV and PTV hotspots were increased 5.47 cGy (0.14%) and 1.22 cGy (0.03%), respectively. Mean mean-dose of exemplar OARs rectum and bladder were increased 2.75 cGy (0.09%) and 9.48 cGy (0.27%), respectively, and hotspot mean increase of 3.32 cGy (0.07%) and 8.63 cGy (0.18%), respectively. Changes were not correlated with volume of contrast and not significantly different with entire bladder override. These results for IV contrast were corroborated across two additional anatomical sites, head and neck and lung, and for oral contrast in rectal cancer plans.
Conclusion
Contrast HU override has a minimal impact on radiation planning dose calculations and may not be a necessary component of planning workflow.