Dosimetric Comparison Of Thoracic Esophageal Squamous Cell Carcinoma Involved Field And Elective Nodal Irradiation

Objective: Esophageal squamous cell carcinoma is a kind of commonly and frequently encountered disease which severely threaten people’s health and life in China. Lack of effective means for early diagnosis, the prognosis of esophageal cancer patients are usually very poor, Radiotherapy and chemotherapy are the major treatments for esophageal cancer. Just for radiation therapy, radiation therapy technology continues to progress with the development, given the control and dose for high-energy photon beams during radiotherapy has reached the point of perfection. At present, radiotherapy for esophageal carcinoma has entered the intensity modulated radiotherapy(IMRT), image guided radiotherapy(IGRT) times. However, in clinical practice, the efficacy of radiotherapy for esophageal carcinoma has not been significantly improved, is still faced with the common problems of local recurrence after treatment and radiation damage. How to increase the target dose and avoid radiation damage is the current research focus. Currently, There are still some controversy for the outline of thoracic esophageal lymphatic drainage area, there are two main programs, the one is elective nodal irradiation(ENI), based on the different parts of the primary cancer, have three cases: upper segment, painting 1, 2, 4, 5, 7 group of lymph nodes and positive area; middle segment, painting 2, 4, 5, 7 group of lymph nodes and positive area; and the lower segment, painting 4, 5, 7, 16, 17 group of lymph nodes and positive area. Another is involved field irradiation(IFI), outlined an area of positive lymph nodes only. A dosimetric study was performed to compare advantage and disadvantage between IFI and ENI on locally advanced esophageal squamous cell carcinoma. Methods: The CT scan data sets of 40 patients of locally advanced thoracic esophageal squamous cell carcinoma were collected. All patients were outlined according different clinical target volume of lymph nodal(CTVln) contouring principle. The plans were managed using IMRT for these patients. The dosimetry of the planning target volumes(PTV-CTVln), the organ at risks(OARs) and the healthy tissue were evaluated. The dose prescription was set to 66 Gy to the primary tumor and 52.8Gy to the PTV-CTVln in 33 fractions. Each fraction applied daily, five fractions per week. Results: Both IMRT plans of different lymph node irradiation principle had reached clinical treatment’s requirement. The maximum dose(D2), mean dose(D50), and minimum dose(D98) in elective nodal irradiation for PTV-GTV were(7080.806±150.992)c Gy,(6780.198±136.898)c Gy,(6093.175±155.665), in involved field irradiation were(7067.165±168.682)、(6785.798±112.371) 、(6193.810±169.786) c Gy(P>0.05), Respectively. The conformity index(CI) was 0.9735±0.0099、0.9756±0.0132, Homogeneity index(HI) was 0.1454±0.0333、0.1327±0.0397,(P>0.05). For patients with different N stage and primary compared with involved field irradiation and elective nodal irradiation, the Dmean, V5,V10,V20 and V30 of all lungs and the Dmean, V30 and V40 of heart, the Dmax of spinal cord was decreased significantly(P < 0.05). Conclusion: For locally advanced thoracic esophageal squamous cell carcinoma, both IMRT of involved field irradiation or elective nodal irradiation reached the clinic requirement. The involved field irradiation can protect significantly OARs.