To optimize the parameters of Monaco planning system based intensity-modulated radiotherapy (IMRT) plan for cervical and upper thoracic esophageal cancer.

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.

The three-field radiotherapy plan had significantly lower V_95% (a PTV1 volume parameter) than the other radiotherapy plans (P<0.05). The volume parameters and dose parameters of PTV2 in each IMRT plan had no significant difference (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). Among the IMRT plans, the nine-field plan had the longest therapy time and the poorest therapeutic effect (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), and there was no significant difference between the plan at V₅, V₁₀, and V_60, (P>0.05).

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.