Impact of setup errors on dose distribution of intensity modulated radiotherapy for patients with esophageal carcinoma

Objective To measure the setup errors in patients with esophageal carcinoma during the treatment of intensity modulated radiotherapy( IMRT) by electronic portal imaging device( EPID),so as to analyze the impact of setup errors on dose distribution of target volume and normal tissues around and verify the rationality on expanding margin of the planning target volume. Methods The setup errors of 36 patients with esophageal cancer were measured once a week for 6 times by EPID. The setup errors were integrated into the XIO treatment planning system by moving the isocenter,and then the dose distribution of GTV,CTV and normal tissues were recalculated. Results The setup errors of the 36 patients in the direction of Z-,X- and Y-axis were 2. 43 ± 1. 80,2. 56 ±1. 87 and 3. 53 ± 2. 82 mm,respectively. The dose covered 95% GTV( D95) was reduced by 50 c Gy,and CTV D95 by 78. 21 c Gy. The lung V20 in the original plan and the integrated plan was 24. 34% and 23. 52%,respectively( P 0. 05). The average dose of the heart in the two plans was 2 067. 23 and 2 021. 23 c Gy,respectively( P 0. 05). In the original plan,no patient had maximum dose of spinal cord over 4 500 c Gy. While in the integrated plan there were 12 patients with the spinal cord dose more than 4 500 c Gy,with a maximum dose of 5 602. 70 c Gy. Conclusion The setup errors cause significant dose reduction of GTV and CTV; the maximum dose of the spinal cord in some patients exceeds 4 500 c Gy,but the dose of the lung and the heart decreases due to the setup errors.