Parameter optimization of intensity-modulated radiotherapy plan in cervical and upper thoracic esophageal cancer

Abstract

Objective To optimize the parameters of Monaco planning system based intensity-modulated radiotherapy (IMRT) plan for cervical and upper thoracic esophageal cancer. Methods Eleven esophageal cancer patients treated at the Radiotherapy Department of Affiliated Hospital of North Sichuan Medical College were selected and included in this study. Under specified conditions, all the patients underwent CT simulation. The physicists set the optimization parameters, changed the number of radiation fields to establish different IMRT plans, and analyzed the data on tumor target volume, organs at risk, and normal tissue of different plans to obtain the optimal radiotherapy plan. Results The three-field radiotherapy plan had significantly lower V95% (a PTV1 volume parameter) than the other radiotherapy plans (P 0.05). The thyroid gland, trachea, and spinal cord in different irradiation field plans had no significant difference in risk. The irradiated volume of the lungs was the largest in the V10, V20, and V30 three-field plan, and smaller in the five-, seven-, and nine-field plans (P 0.05). The undefined normal tissue was larger in the V20, V30, V40, and V50 three-field plan than in the other plans (P 0.05). Conclusion Using the Elekta Monaco 3.2 IMRT radiotherapy planning system and selecting the size of 4.000 cm2 as the minimum field, the area of 3.000 cm2 as the minimum change, 0.60 cm as the minimum width of leaf, and 6 MU as the minimum hop number, the five-field and seven-field plans are more suitable than the others in cervical and upper thoracic esophageal cancer. Key words: Esophageal cancer; IMRT; Radiotherapy plan; Radiation fields