Dosimetric Comparison of Intensity Modulated Radiotherapy and Simultaneous Integrated Boost Techniques in the Treatment of Glioblastoma Multiforme

Aim: The aim of this study was to compare dosimetric advantages of using intensity-modulated radiation therapy (IMRT) and simultaneous-boost (SIB-IMRT) techniques for glioblastoma multiform (GBM). Materials and Methods: Ten patients with GBM were retrospectively selected between the years of 2020 and 2021. For all patients, two treatment plans were created. The plans were calculated using anisotropic analytical algorithm with 6 MV photon energy. Treatment doses were 50 Gy for planned target volume (PTV) (50 Gy), 10 Gy for PTV (60 Gy) and 60 Gy for PTV (60 Gy), which is planned as 2 Gy per daily fraction in IMRT technique. In the SIB-IMRT technique, which provides different dose levels in target volumes simultaneously in 25-day fractions, was used. All plans were compared with respect to the doses received by PTV and the organ at risk including brain system, optic chiasma, optic nerves, eyes, the dose homogeneity index (HI), conformity indexes (CI) and total monitor unit counts required for the treatment. Results: The average doses for PTV were 60.62±0.33 Gy for the IMRT technique and 60.58±0.32 Gy for the SIB-IMRT technique. The average doses for PTV, for both techniques were found to be similar. The average HI value for PTV (60 Gy) was 0.05±0.009 in IMRT, 0.13±0.197 in SIB-IMRT, 0.97±0.02 in IMRT, and 0.35±0.06 in SIB-IMRT, respectively. As a result of the statistical comparison, a significant difference was observed in HI and CI values between IMRT and SIB-IMRT in the analysis of the values of PTV (p=0.004, p=0.001). When the SIB-IMRT plans were compared with the IMRT plans, it was observed that the mean doses received by critical organs such as optic chiasma, optic nerve, and eye were significantly decreased in the SIB-IMRT technique (p=0.000). Conclusion: When the IMRT technique for GBM treatment was compared with the SIB-IMRT technique, SIB-IMRT provided better protection for organ at risk. SIB-YART plans may be clinically acceptable treatment modalities for GBM cancers.