Dosimetric differences between intensity-modulated radiotherapy based on equivalent uniform dose and dose-volume optimization in stage III non-small cell lung cancer

Objective: To determine the dosimetric differences between biological and physical functions of equivalent uniform dose (EUD) and dose volume (DV) therapy in patients with phase III non-small cell lung cancer. Methods: Four different radiotherapy plans (DV+DV, DV-EUD+DV, EUD+EUD and EUD-DV+EUD) were developed for 15 patients with stage III NSCLC. To study physical function (DV+DV) the target area was optimized by introducing the conditions of biological function optimization, while the organs at risk were optimized by means of physical function (DV-EUD+DV). Biological function optimization (EUD+EUD) was performed for the target area by applying conditions of physical function optimization while biological function optimization (EUD-DV+DV) was conducted for the organs at risk to compare dosimetric parameters among the four groups of treatment plans. Results: PTV: D-2%, D-98%, D-50%, V-105% and D-max of both the DV-EUD+DV group and EDU-DV+EUD group were the minimum (P < 0.05). The minimum and average dose of the EUD+EUD group showed an increasing trend and high-dose area became observable. For homogeneity index (HI), DV-EUD+DV group and EUD-DV+EUD results were compared with the other groups (P < 0.05), no significant difference was observed statistically between the DV-EUD+DV group and EUD DV+EUD (P=0.659). With regard to conformability index (CI), the results of the four groups showed no significant difference (P > 0.05). For the organs at risk, the mean dose of lung tissue (MLD), V-5, V-10, V-20, V-30, heart V-30, V-40, and D-mean also revealed no significant difference (P > 0.05). For the spinal cord, the D1 % of the EUD+EUD group and EUD-DV+EUD groups were significantly different (P < 0.05) than the other groups. While no significant difference (P=0.32) was found between the EUD+EUD and EUD-DV+EUD groups. When comparing the number of machine unions (MU) no significant difference was revealed (P > 0.05) among the results of the 4 groups. Conclusion: The methods featuring optimization of physical and biological functions are effective in improving the uniformity of target area to have better outcome of the treatment. Biological function optimization or the combination of biological and physical function optimization is conducive to significantly reduce the required dose for the spinal cord.