Magnetic Resonance Imaging (MRI) is increasingly being used for improving tumor delineation and tumor tracking in the presence of respiratory motion. The purpose of this work is to design and build an MR compatible motion platform and to use it for evaluating the geometric accuracy of MR imaging techniques during respiratory motion. The motion platform presented in this work is composed of a mobile base made up of a flat plate and four wheels. The mobile base is attached from one end and through a rigid rod to a synchrony motion table by Accuray® placed at the end of the MRI table and from the other end to an elastic rod. The geometric accuracy was measured by placing a control point‐based phantom on top of the mobile base.In‐house software module was used to automatically assess the geometric distortion. The blurring artifact was also assessed by measuring the Full Width Half Maximum (FWHM) of each control point. Our results were assessed for 50, 100, and 150 mm radial distances, with a mean geometric distortion during the superior–inferior motion of 0.27, 0.41, and 0.55 mm, respectively. Adding the anterior–posterior motion, the mean geometric distortions increased to 0.4, 0.6, and 0.8 mm. Blurring was observed during motion causing an increase in the FWHM of ≈30%. The platform presented in this work provides a valuable tool for the assessment of the geometric accuracy and blurring artifact for MR during motion. Although the main objective was to test the spatial accuracy of an MR system during motion, the modular aspect of the presented platform enables the use of any commercially available phantom for a full quality control of the MR system during motion.
Purpose: Calibration curve (CC) for EBT2 film dosimeters is mainly dependend on film batch, film scanning and analysis conditions. CC errors are translated to 2D dosimetry errors. Aiim of study is to present a methodology for using EBT2‐films for accurate 2D relative dose measurements without need of an accurate CC. Methods: A batch of EBT2 films has been used for calibration irradiations using doses up to 2500 cGy. An arbitrary parameter (AP) (inverse pixel intensity using ImageJ software) was used as the dependent variable in a film dose response relationship. Linear dose‐response region was evaluated. Within this dose region, the relative changes of dose (D%) equals the relative changes of the APnet = [(AP‐APbackground)%]. A film from same batch was irradiated using a Stereotactic Radiosurgery treatment plan (Maximum dose lied within the linear film dose range). The film derived relative dose map was compared against corresponding TPS calculations using Gamma Index (2%, 2mm)Results: Linear Dose AP response was observed for doses up to ∼400 cGy. Therefore, within this dose range, (D%) = (APnet%). 2D map of measured SRS irradiated EBT2 film (Apnet%) values have been measured and compared to corresponding TPS calculation (D%) values. Satisfying agreement between the two data sets was observed (gamma <1 for ∼96% of the pixels). Conclusion: EBT2 films can be used for accurate 2D relative dose measurements as long as they are irradiated within the dose range of 0 to 400 cGy and their batch linear dose response is ensured. There is no need to ensure a certain slope of the linear response, but just the linearity of response itself. Since films are mainly useful for relative rather than absolute dose measurements, the proposed methodology could offer a simple solution for 2D dosimetry in a large number of radiotherapy QA and/or plan verification purposes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.