Evaluation of positioning uncertainty for frameless radiosurgery for three IGRT methods with a head phantom

Abstract

Introduction A BRAINLAB system for frameless radiosurgery is commissioned obtaining patient positioning accuracy with the STEEV head phantom (CIRS). Purpose Firstly the position accuracy for frameless radiosurgery has been compared with three different IGRT methods: EXACTRAC (BRANLAB), OBI-2D (VARIAN) and CBCT (VARIAN) with EXACTRAC registration. Secondly the uncertainty of image registration between MRI (PHILIPS INGENIA SYSTEMS 3.0T) and CT (PHILIPS BIG BORE) has been evaluated with IPLANRT image 4.1.1 software. Materials and methods Phantom positioning was done with automatic registration and with equivalent X-ray parameters for the three IGRT methods. Measurement was done 5 times, every of these the phantom with mask was replaced. Position accuracy was evaluated with the tool “detect Winston-Lutz pointer” from EXACTRAC. CT and MRI images of a multimodality fillable sphere insert in the phantom were registered. The registration was evaluated with IPLANRT image software finding the center of the sphere in each modality. Results For the three IGRT techniques the accuracy obtained was (0.466 ± 0.071)mm for EXACTRAC, (0.744 ± 0.209)mm for OBI-2D and (0.750 ± 0.386)mm for CBCT registered with EXACTRAC. For MRI was obtained (0.300 ± 0.1)mm. The total uncertainty for EXACTRACT IGRT system is (0.554 ± 0.374)mm (k = 2). Conclusions • The positioning system EXACTRAC have less uncertainty than both OBI-2D and CBCT registered with EXACTRAC for cranial SRS. • The total uncertainty for the EXACTRAC including IGRT and also image registration between CT and MRI is (0.554 ± 0.374)mm.