The effect of lipiodol on dose distribution of carbon ion therapy after transcatheter arterial chemoembolization

Objective To investigate the effect of lipiodol as embolization agents in liver, after transcatheter arterial chemoembolization, on dose calculation under the carbon ion treatment plan. Methods The actual relative linear stopping powers(RLSP)in pure lipiodol, pure gel and lipiodol-gel mixture, together with the correctd RLSPs from their CT images, were compared.In seven typical cases with lipiodol deposition area, carbon ion treatment plan was performed for the original lipiodol images.Successively on the basis of analysis that has made, the RLSP in lipiodol deposition area was corrected to be as in normal liver tissue, for which the carbon ion treatment plan was again performed.A comparison was made of differences in water equivalent depth (WED) and dose distribution on different CT images. Results The RLSP value corrected according to CT image HU value, lipiodol, and lipiodol-gel mixture may increase by 4.6%-139.0% compared with the measured value. In seven typical cases, deposited lipiodol can cause WED to increase by (0.89±0.41) cm along the field track and RBE by(3.83±1.71)Gy within the 1 cm of distal area of target. Conclusions In order to improve the accuracy of dose distribution calculation, the HU value and/or RLSP in deposited lipiodol area in liver after transcatheter arterial chemoembolization should being corrected to be as in the normal liver tissue. Key words: Transcatheter arterial chemoembolization; Lipiodol; Carbon-ion; Relative stopping power