COMPARISON OF COPLANAR AND NON- COPLANARVMAT FOR BRAIN CANCER BY USING THE DOSIMETRICAL AND RADIOBIOLOGICAL INDICES

Background: Recent techniques of radiotherapy such as volumetric modulated arc therapy (VMAT) that delivered in Coplanar technique or non-coplanar technique allows to deliver high doses to the brain tumors, at the same time reducing the risk of normal tissues as compared with intensity modulated radiotherapy (IMRT) and the three-dimensional conformal radiotherapy (3D-CRT). Aim: The aim of the current work is to compare dosimetrical and radiobiological indices of treatment plans for brain tumor using CO-VMAT and NC-VMAT techniques to choose the optimum technique for the treated cases. Patients and methods: Twenty-one cases with brain tumors were performed for the treatment planning study. The cases are planned by using the coplanar and non coplanar VMAT techniques and optimized to evaluate and compare dosimetrical and radiobiological parameters related to PTV dose coverage and sparing of organs at risk. The total dose of CO-VMAT and NC-VMAT plans is 60 Gray in 30 fractions during a single phase with a daily dose of 2 Gray. Results: In dosimetrical calculations, CO-VMAT and NC-VMAT techniques gave similar (homogeneity index HI, modified homogeneity index MHI, conformity index CI and quality factor QF) values for the PTV, while CO-VMAT was the higher in (target coverage index TCI, prescription isodose to target volume ratio PITV and conformity number CN) values and the lower in (gradient index GI, gradient measure GM) values, and NC-VMAT was the lower in Monitor units MUs values. In radiobiological calculations, equivalent uniform dose EUD values, tumor control probability TCP and complication free tumor control probability P+ were large in CO-VMAT and normal tissue complication probability NTCP was less in NC-VMAT. Conclusion: While the previous studies showed that CO-VMAT technique was used when the tumor is far from the organs at risk, the present work found CO-VMAT can be used when the tumor is near to or far from organs at risk (OARs) because it can achieve the target dose coverage and sparing of OARs together. We strongly recommend that NC-VMAT technique should be used when the OARs are located inside the tumor to be able to achieve more sparing of them.