Comparison of Dose Distribution in Brain Tumor Conformal Radiotherapy Using CT and CBCT

Abstract

Objective: To research the value of cone-beam CT (CBCT) in dose re-calculation in IGRT by compared with dose distribution using CBCT to CT. Method:To measure CT value of materials in phantom and compare with standard CT value by CBCT images of phantom. Besides 5 patients with brain tumor was selected, completed CT-simulation. Based the CT images, a conformal treatment plan was completed in Pinnacle3 TPS. In the beginning 1 week of treatment, 5 serieses on-board images of this patient were obtained. The treatment plan, which was designed using the CT images, was fused with the 5 CBCT images respectively. After dose re-calculating, the differences of CT value and dose of iso-centre, GTV and normal tissue (such as eyes) were gotten. Results:Between the measured and standard CT value in phantom test, the maximum was 22 HU. The homogeneity of CBCT image edge is not very good, the maximum about it was 16HU. Between the plan using CT and 5 plans using CBCT, the maximum of dose on iso-centre was ±2%; the maximum of CT value of PTV was 22 HU, and dose on it were±2%; the maximum of CT value of eyes were 75 HU, and dose on them were ±5%; the maximum of CT value of brain was 16 HU, and dose on it were ±1%. The maximum of total MU of 6 plans were 5 MU.Conclusion:From the comparison results, it could be concluded that the differences of CT value and dose distribution in plans using CBCT and CT were almost ignored. So CBCT, instead of CT, could be used in dose calculation, which offers a feasible individual Image-Guided Radiotherapy.