Impact of setup errors on dose distribution of three dimensional conformal radiotherapy for patients with esophageal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective To measure the setup errors of patients with esophageal carcinoma during the treatment of three dimensional conformal radiotherapy (3DCRT), and to analyze the impact of setup errors on dose distribution of GTV,CTV and normal tissues around. Methods Forty-two patients with esophageal cancer treated by 3DCRT were included. The setup errors of each patient were measured once a week for 6 times by electronic portal imaging device (EPID). The setup errors were integrated into the treatment plan-ning system by moving the isocenter. Then the dose distribution of GTV, CTV and normal tissues were recal-culated. Results The systematic setup errors of the 42 patients were - 2.31 mm, - 0.55 mm and - 0.16 mm, and the random errors were 4.42 mm, 4.35 mm and 4.48 mm in the directions of lef-fight, anterior-posterior,and superior-inferior, respectively. The dose covered 95% GTV( D95 ) was reduced by 32 cGy and by 88 cGy for CTV D95. The lung V20 in the original plan and the integrated plan was 22.49% and 22.02%, respectively. The average dose of the heart in the two plans was 2077.62 cGy and 2036.23 cGy, respectively. In the original plan, no patient had maximum dose of spinal cord over 4500 cGy; While in the intergrated plan there were 18 patients had the spinal cord dose more than 4500 cGy, with a maximum dose of 5503.90 cGy. Conclusions The setup errors cause significant dose reduction of GTV and CTV, but not of the lung and heart . The maximum dose of the spinal cord may exceed 4500 cGy due to the setup errors.