Dosimetry comparison with helical tomotherapy, volumetric modulated arc therapy, and intensity-modulated radiotherapy for grade II gliomas: A single-institution case series

Radiotherapy is an essential postoperative treatment for grade II gliomas. However, comparative dosimetric studies of different radiotherapy plans for grade II gliomas are still lacking. Therefore, we conducted this case series analysis to compare the dosimetric differences among helical tomotherapy (TOMO), volumetric modulated arc therapy (VMAT), and intensity-modulated radiotherapy (IMRT) for grade II gliomas. To achieve that, seven diagnosed postoperative patients with grade II gliomas were analyzed by computed tomography and then planned with TOMO, VMAT, and IMRT. The plan target volume (PTV) prescribed dose was 50 Gy (daily fraction of 2.0 Gy, 5 days/week). The expected treatment efficiency was measured by monitor units (MUs) scoring. Treatment plans of the patients were compared in the quality of target volumes dosage coverage, the efficiency of dosage delivery, and the dosage exposure of normal adjacent organs at risk (OAR). Differences in each method were measured by utilizing the Nonparametric ANOVA. The study shows that TOMO achieved a significantly higher PTV-D98% (doses received by 98% of the PTV volume) than VMAT and IMRT (50.30 +/- 0.13 vs 49.21 +/- 0.19, p = 0.006; 50.30 +/- 0.13 vs 49.78 +/- 0.18, p = 0.014), while there was no difference in PTV-D2% (doses received by 2% of the PTV volume). IMRT achieved a conformity index (CI) preferably, and TOMO generated a favorable homogeneity index (HI) (p < 0.05 for both). The MUs were fewer for VMAT than IMRT and TOMO (294 +/- 19, 572 +/- 24, 317 +/- 97, respectively). IMRT achieved better protection for the lens and brain stems. Our case series study indicated that TOMO, VMAT, and IMRT achieved a comparatively good target dosimetric coverage, and most OARs were protected well. IMRT is not inferior to TOMO and VMAT and is still very suitable for treating most grade II glioma patients.