Dosimetric comparison of non-coplanar three-dimensional conformal radiation therapy (nc3DCRT) planning and radio biologically optimized partial arc volumetric modulated arc therapy (VMAT) planning of unilateral brain tumours – A retrospective study

Aim: To compare non-coplanar 3DCRT planning and partial arc VMAT planning dosimetrically for unilateral brain tumours.Introduction:Intensity modulated radiation therapyhas gainedwide popularity as a radiotherapy treatment of choice for many clinical sites. Volumetric modulated arc therapy is a kind of therapy in which rather than using multiple static fields at different gantry angles, one or multiple full or partial arcs are used for radiotherapy planning and treatment. Its ability to provide superior target coverage and better normal tissue sparing makes it a treatment of choice over conventional and 3DCRT radiotherapy planning techniques. But, on the same time volume of low dose region which can increase probability of secondary malignancy in VMAT planning is reported to be on the higher side. Our study compares various parameters of plan quality along with low dose volumes in the techniques under comparison.Materials and methods:10 anonymized patients with unilateral malignant brain tumours previously treated with nc3DCRT were selected for the study and planned with partial arc VMAT. Conformity Index, Homogeneity Index, Target Coverage, Doses to critical structures and normal brain were compared.Conclusion:In our study by using VMAT technique we were able to reduce doses to critical structures (Brainstem, optic nerves, and optic chiasm) significantly, got better target coverage along with lesser number of MUs per fraction and significant reduction in low dose volume and reduction in doses to contralateral normal structures including lesser amount of low dose volume.