Changing Trends in Radiotherapy for Glioblastoma Multiforme and Effects on Normal Tissue Doses

Abstract

Introduction:The aim of the study is to reveal the changing trends in radiotherapy (RT) for glioblastoma multiforme (GBM) from past to present and to show the changes in organs at risk (OARs) doses.Methods:We re-planned 10 GBM patients who were previously irradiated. Rigid fusion was performed through pre- and postoperative magnetic resonance imaging (MRI) and simulation computed tomography, and 9 separate volumes were created. While volumes varied from whole brain RT (WBRT) to postoperative two-phase irradiation, RT application ranged from 2-dimensional Co-60 treatment to 3-dimensional volumetric modulated arc therapy (VMAT). OARs were contoured, and doses were noted. A 3 dimensional-conformal RT (3D-CRT) plan of the volume created by preoperative MRI was compared to 3D-CRT and VMAT plans generated by postoperative MRI. Statistical analysis was performed using Paired sample t-test.Results:During the time of WBRT, normal brain tissue was receiving 45-60 Gy. Through VMAT, the median brain-planning target volume (PTV) Dmean decreased to 35 Gy. According to both PTV-Radiation Therapy Oncology Group (RTOG)preop and PTVRTOGpreop 3D-CRT plannings, there was no difference in all OARs doses between plans, including brain-PTV initial volume Dmean and brain-PTV boost Dmean doses. Significantly lower OARs doses were obtained from 3D-CRT plans based on both PTV-RTOGpreop and PTV-RTOGpostop volumes with the VMAT planning.Conclusion:With changing trends in RT for GBM, there has been a significant decrease in treatment volumes and normal tissue doses. According to the postoperative volume definition of RTOG, lower normal tissue doses are obtained from VMAT plans, compared to the conformal treatment plans.

Keywords

• 3D conformal radiotherapy
• intensity modulated radiotherapy
• glioblastoma multiforme
• volumetric modulated arc therapy