The dosimetry effect of setup errors for patients with esophageal carcinoma in IG-IMRT

The study aims to measure the setup errors of patients with esophageal carcinoma during the treatment of three dimensional conformal radiotherapy (3DCRT). Through the simulation of the three dimensional treatment planning, evaluate the dosimetry effect of setup errors to GTV, CTV and normal tissues around in the actual treatment. From January 2007 to January 2008, 42 chosen patients with esophageal cancer were given 3DCRT. By applying the EPID, the setup errors were measured. Each patient would be examined six times during the treatment, with the frequency of once a week. The simulation of the setup errors can be achieved by moving the isocenter and then observe and analyze the dose distribution of GTV, CTV and normal tissues. There are three main results. The first one is that the systematic setup errors of the 42 patients, from leftward to rightward, was -2.31mm, and the random errors was 4.42mm, while form forward to backward, the systematic setup errors was -0.55mm, while the random errors was 4.35mm, and form upward to downward, the data were -0.16mm and 4.48mm, respectively. The second one is that the setup errors resulted in dose reduction of GTVD95 with 32cGy and CTVD95 with 88cGy. The last one is that the V20 of lung for PLAN1 and PLAN2 were 22.49±5.20% and 22.02±5.47% respectively. The average doses of heart for PLAN1 and PLAN2 were 2077.62±1292.75cGy and 2036.23±1295.86cGy. In the original plan, no patients whose maximum dose of spinal cord exceeded 4500cGy, while 18 cases (42.86%) in PLAN2 were more than 4500cGy, the maximum dose was 5503.90cGy. In the end, the conclusion is the setup errors lowered the level of dose distribution in the original plan so as to reduce the dose of GTV and CTV, while the doses of lung and heart did not change obviously, however, some patients whose maximum dose of spinal cord may exceeded 4500cGy.