Effect of 6 MV and 10 MV Flattening Filter-Free X-Ray Beams on Intensity Modulated Radiotherapy for Rectal Cancer

Abstract

Objective: To explore the influence of 6 MV X-ray and 10 MV X-ray on the VMAT plan of rectal cancer in flattening filter-free (FFF) mode, and to provide a reference for the selection of radiation quality for rectal cancer radiotherapy. Methods: Twenty patients with rectal cancer after surgery were selected for retrospective analysis, and the VMAT plan of FFF-6 MV and the VMAT plan of FFF-10 MV were designed on the Eclipse 13.6 planning system. The dose volume histograms of the two plans, the conformity index (CI) of the target area, the homogeneous index (HI) and the dosimetry parameters of the bladder, left and right femoral heads, small intestine, and normal tissues (B-P), and the dose verification passed Rate, Monitor unit count, treatment time difference were compared. Results: The D2 and Dmean differences between 6 MV X-ray and 10 MV X-ray plans were statistically significant (P 0.05). CI and HI in the 6 MV plan group were better than those in the 10 MV plan group (P 0.05), the result of V50 of 6 MV was less than 10 MV plan (P 0.05), normal tissue V2 and V5 were 10 MV Lower than the 6 MV plan (P < 0.05). The passing rate of dose verification, the number of monitor unit, and the treatment time were all in the 6 MV plan less than the 10 MV plan (P < 0.05). Conclusion: Both plans could meet the clinical requirements, considering that most of the organs at risk have no significant difference, and the conformity index (CI) and uniformity index (HI) of the target area at 6 M X energy in FFF mode are better than 10 MV X-ray, and the number of monitor units is less, it is recommended to use 6 MV X energy to develop a rectal cancer VMAT plan in FFF mode.