Investigation of Predictors to Achieve Acceptable Lung Dose in T-Shaped Upper and Middle Esophageal Cancer With IMRT and VMAT

PURPOSE: The purpose of this study is to investigate whether there are predictors and cutoff points that can predict the acceptable lung dose using intensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) in radiotherapy for upper ang middle esophageal cancer. MATERIAL AND METHODS: Eighty-two patients with T-shaped upper-middle esophageal cancer (UMEC) were enrolled in this retrospective study. Jaw-tracking IMRT plan (JT-IMRT), full-arc VMAT plan (F-VMAT), and pactial-arc VMAT plan (P-VMAT) were generated for each patient. Dosimetric parameters such as MLD and V20 of total lung were compared among the three plannings. Ten factors such as PCTV(inferior) length and PCTV(inferior) length/total lung length were calculated to find the predictors and cutoff points of the predictors. All patients were divided into two groups according to the cutoff points, and the dosimetric differences between the two groups of the three plans were compared. ANOVA, receiver operating characteristic (ROC) analysis, and Mann–Whitney U-test were performed for comparisons between datasets. A p <0.05 was considered statistically significant. RESULT: The quality of the targets of the three plannings was comparable. The total lung dose in P-VMAT was significantly lower than that in JT IMRT and F-VMAT. Monitor unit (MU) of F-VMAT and P-VMAT was significantly lower than that of JT IMRT. ROC analysis showed that among JT IMRT, F-VMAT, and P-VMAT, PCTV(i-L), and PCTV(i-L)/TL(L) had diagnostic power to predict the suitability of RT plans according to lung dose constraints of our department. For JT IMRT, the cutoff points of PCTV(i-L) and PCTV(i-L)/TL(L) were 16.6 and 0.59. For F-VMAT, the cutoff points of PCTV(i-L) and PCTV(i-L)/TL(L) were 16.75 and 0.62. For P-VMAT, the cutoff points of PCTV(i-L) and PCTV(i-L)/TL(L) were 15.15 and 0.59. After Mann–Whitney U-test analysis, it was found that among the three plannings, the group with lower PCTV(i-L) and PCTV(i-L)/TL(L) could significantly reduce the dose of total lung and heart (p <0.05). CONCLUSION: PCTV(i-L <)16.6 and PCTV(i-L)/TL(L) <0.59 for JT IMRT, PCTV(i-L <)16.75 and PCTV(i-L)/TL(L) <0.62 for F-VMAT and PCTV(i-L <)15.15, and PCTV(i-L)/TL(L) <0.59 for P-VMAT can predict whether patients with T-shaped UMEC can meet the lung dose limits of our department.