Influence of Intravenous Contrast Medium on Dose CalculationUsing CT in Treatment Planning for Oesophageal Cancer

Objective: To evaluate the effect of intravenous contrast on dose calculation in radiation treatment planningfor oesophageal cancer.
Methods: A total of 22 intravein-contrasted patients with oesophageal cancer wereincluded. The Hounsfield unit (HU) value of the enhanced blood stream in thoracic great vessels and heart wasoverridden with 45 HU to simulate the non-contrast CT image, and 145 HU, 245 HU, 345 HU, and 445 HU tomodel the different contrast-enhanced scenarios. 1000 HU and -1000 HU were used to evaluate two non-physiologicextreme scenarios. Variation in dose distribution of the different scenarios was calculated to quantify the effectof contrast enhancement.
Results: In the contrast-enhanced scenarios, the mean variation in dose for planningtarget volume (PTV) was less than 1.0%, and those for the total lung and spinal cord were less than 0.5%. Whenthe HU value of the blood stream exceeded 245 the average variation exceeded 1.0% for the heart V40. In thenon-physiologic extreme scenarios, the dose variationof PTV was less than 1.0%, while the dose calculations ofthe organs at risk were greater than 2.0%.
Conclusions: The use of contrast agent does not significantly influencedose calculation of PTV, lung and spinal cord. However, it does have influence on dose accuracy for heart.