RTHP-01. COMPARISON OF CO-PLANAR AND NON-COPLANAR TREATMENT PLANNING FOR TUMOR NEARBY CRITICAL ORGANS IN HIGH GRADE GLIOMAS

Abstract

The goal of this study was to compare six treatment planning methods (IMRTand VMAT) for high grade gliomas that had PTVs overlapping the optic pathway and/or brainstem. METHOD AND MATERIALS:27 previously treated patients were replanned with IMRT5,IMRT7,IMRT7-non, VMAT2f, VMAT2hand VMAT2h-non.For this comparison study, it was selected in three different localization (right, left and center sided tumors) of the tumor. PTVoptics and PTVbrainstem was limited to a maximum dose limit equal to 54Gy and minimum dose limit of 51Gy. A comparison of the three IMRT plans with three VMAT plans were performed in all 27 patients. The mean dose of the PTV was 60.16 ± 46.84 in IMRT5, 60.31 ± 47.48 in IMRT7, 60.30 ± 51.64 in IMRT7-non, 60.22 ± 55.32 in VMAT2f, 60.18 ± 94.51 in VMAT2h and 60.36 ± 84.11 in VMAT2h-non.The mean CI was significantly higher with the all IMRT plans, compared to all VMAT plans (p<0.05 for all comparisons) in left and right sided tumors. There was also significant differences between coplanar and non-coplanar plans in IMRT and VMAT plans in right sided tumors (p<0.05). IMRT5,IMRT7,IMRT7-non,VMAT2f,VMAT2h and VMAT2h-non resulted in mean doses to brainstem of 23.79Gy, 23.6Gy, 24.77Gy, 23.43Gy, 24.64Gy and 24.23Gy, respectively. Only in center sided tumors, there were significant differences between coplanar and noncoplanar plans in brainstem mean doses(IMRT5-IMRT7-nonp=0.00849, IMRT7-IMRT7-nonp=0.011, IMRT5-VMAT2h-nonp=0.0153 and VMAT2f-VMAT2h-nonp=0.0166). Radiation doses to the ipsilateral optic nerves mean, ipsilateral lens mean, ipsilateral retina mean and maximum, contralateral optic nerves mean and maximum, contralateral retina mean, contralateral lens mean and maximum and optic chiasm maximum were higher with the VMAT2f plans than with the all of IMRT plans (IMRT5,IMRT7 and IMRT7-non) in the right and left sided tumors. While VMAT2f plans had a significantly longer delivery time than VMAT2h and VMAT2h-non (p=0.0003), the absolute difference in the mean treatment time was not so large. IMRT techniques provided better target coverage than VMAT plans. VMAT techniques reduced treatment delivery time compared to IMRT techniques.