Simultaneous integrated boost (SIB) for treatment of gynecologic carcinoma: Intensity-modulated radiation therapy (IMRT) vs volumetric-modulated arc therapy (VMAT) radiotherapy

The aim of this study was to quantitatively compare dosimetric criteria between intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans for patients undergoing radiation treatment of gynecologic carcinoma with a simultaneous integrated boost (SIB) technique. IMRT and VMAT plans were retrospectively analyzed for 20 patients. The elective volume was planned to receive 45 Gy in 25 fractions of 1.8 Gy, with the integrated boost volume (involved nodes) receiving 55 Gy simultaneously. The same dose constraints were employed during the optimization of both techniques. IMRT plans consisted of 9 to 11 fields at equally spaced gantry angles. VMAT plans consisted of 3 full arcs of 360°. A large variety of dose metrics across planning target volume (PTV)45, PTV55, bladder, rectum, sigmoid, bowel, kidneys, and femoral heads were extracted per patient, per plan. Conformity and homogeneity indices were also calculated and compared for each target volume. The total number of monitor units as well as the integral dose was also compared between IMRT and VMAT. The Wilcoxon signed rank test was performed to evaluate any significant differences between parameters, with an applied Bonferroni correction to account for multiple testing (significance level, p < 0.0006). The results demonstrate the equivalence of the 2 planning techniques across all studied parameters, with the exception of the expected decrease in monitor units that VMAT is capable of achieving. The findings of this study suggest that IMRT and VMAT are both acceptable options for applying simultaneous integrated boost techniques for the treatment of gynecologic cancers. The technique of choice will be dependent on departmental resources and should be considered on a case-by-case basis.