Target bias and dose study of patients with esophageal carcinoma during the treatment of three dimensional conformal radiotherapy

OBJECTIVE: To observe the bias and volume change of gross tumor volume (GTV) during the treatment of three dimensional conformal radiotherapy(3D-CRT) for esophageal carcinoma by image fusion, to analyze the influence to dose distribution caused by target changes and explore the necessity and feasibility of the second CT simulation. METHODS: Forty patients with esophageal carcinoma were treated by 3D-CRT. After the first radiation of 30 Gy, they were rescanned by CT simulator with the same position and range. The CT images from the second simulation were transferred to the first treatment plan and image fusion was made simultaneously. Two treatment plans were designed for each patient. Plan 1: the total prescription dose of 60 Gy was delivered to PTV1. Plan 2 was designed by two phases, the first one being the same to plan 1. For the second one, prescription dose of 30 Gy was delivered to PTV2. The two-phase plans were fitted to plan 2. The doses of GTV, CTV, PTV were observed. RESULTS: 1) The bias of geometrial center of GTV along X, Y, Z axis was 0.3, 0.7, 0.3 cm, respectively. The volume of GTV2, the maximum transverse and anteroposterior diameter scanned by the seconded CT simulation were significantly smaller than those of the first time, while the length of lesion was not significantly shorter.2) In Plan 1, PTV 2 D 95 was lower than PTV 1 D 95 about 8.38%.3) In Plan 2, PTV 2 D 95 was higher than PTV 1 D 95. 4) PTV 2 D 95 from plan1 was significantly lower in the patients whose length of lesion >7 cm than that ≤7 cm, and the samd as in the patients whose aorta was invasioned than not. CONCLUTIONS: There were target bias and contraction during the treatment of 3D-CRT for esophageal carcinoma. The PTVD 95 decreased about 8.38% due to the bias of target. For the patients whose length of lesion were comparatively long and aorta were invaded, we recommended a second CT simulation to modulate the dose of target.