RESUMO
With the utilization of magnetic resonance (MR) imaging in radiotherapy increasing, routine quality assurance (QA) of these systems is necessary. The assessment of geometric distortion in images used for radiotherapy treatment planning needs to be quantified and monitored over time. This work presents an adaptable methodology for performing routine QA for systematic MRI geometric distortion. A software tool and compatible protocol (designed to work with any CT and MR compatible phantom on any scanner) were developed to quantify geometric distortion via deformable image registration. The MR image is deformed to the CT, generating a deformation field, which is sampled, quantifying geometric distortion as a function of distance from scanner isocenter. Configurability of the QA tool was tested, and results compared to those provided from commercial solutions. Registration accuracy was investigated by repeating the deformable registration step on the initial deformed MR image to define regions with residual distortions. The geometric distortion of four clinical systems was quantified using the customisable QA method presented. Maximum measured distortions varied from 2.2 to 19.4 mm (image parameter and sampling volume dependent). The workflow was successfully customized for different phantom configurations and volunteer imaging studies. Comparison to a vendor supplied solution showed good agreement in regions where the two procedures were sampling the same imaging volume. On a large field of view phantom across various scanners, the QA tool accurately quantified geometric distortions within 17-22 cm from scanner isocenter. Beyond these regions, the geometric integrity of images in clinical applications should be considered with a higher degree of uncertainty due to increased gradient nonlinearity and B0 inhomogeneity. This tool has been successfully integrated into routine QA of the MRI scanner utilized for radiotherapy within our department. It enables any low susceptibility MR-CT compatible phantom to quantify the geometric distortion on any MRI scanner with a configurable, user friendly interface for ease of use and consistency in data collection and analysis.
Assuntos
Imageamento por Ressonância Magnética , Radioterapia (Especialidade) , Humanos , Fluxo de Trabalho , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas , Software , Processamento de Imagem Assistida por Computador/métodosRESUMO
Four methodologies were evaluated for quantifying kilovoltage cone-beam computed tomography (CBCT) dose: the Cone-Beam Dose Index (CBDI), IAEA Report 5 recommended methodology (IAEA), the AAPM Task Group 111 methodology (TG111), and the current dose metric; the Computed Tomography Dose Index (CTDI) on two commercial Varian cone-beam CT imaging systems; the Clinac iX On-Board Imager (OBI); and the TrueBeam X-ray Imaging system (XI). The TG111 methodology measured the highest overall dose (21.199 ± 0.035 mGy OBI and 22.420 ± 0.002 XI for pelvis imaging) due to the full scatter of the TG111 phantom and was within 5% of CTDI measurements taken using a full scatter TG111 phantom and 30-cm film strips. CBDI measured the second highest overall dose, within 10% of the TG111, with IAEA measuring the third highest dose. For head CBCT protocols, CBDI measured the highest dose, followed by IAEA. The CTDI method measured lowest across all scan modes highlighting its limitations for CBCT dosimetry. The XI imaging system delivered lower doses for head and thorax scan modes and similar doses to the OBI system for pelvis scan modes due to additional beam hardening filtration in the XI system. The TG111 method measured the highest dose in the center of a CBCT scan during image guidance procedures; however, CBDI provided a good approximation to TG111 with existing CTDI equipment and may be more applicable clinically.
Assuntos
Tomografia Computadorizada de Feixe Cônico/métodos , Neoplasias/radioterapia , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia Guiada por Imagem/métodos , Radioterapia de Intensidade Modulada/métodos , Cabeça/diagnóstico por imagem , Humanos , Processamento de Imagem Assistida por Computador/métodos , Órgãos em Risco/efeitos da radiação , Pelve/diagnóstico por imagem , Radiografia Torácica , Dosagem RadioterapêuticaRESUMO
INTRODUCTION: Recent advances in image guidance and adaptive radiotherapy could enable gantry-free radiotherapy using patient rotation. Gantry-free radiotherapy could substantially reduce the cost of radiotherapy systems and facilities. MRI guidance complements a gantry-free approach because of its ability to visualise soft tissue deformation during rotation. A potential barrier to gantry-free radiotherapy is patient acceptability, especially when combined with MRI. This study investigates human experiences of horizontal rotation within an MRI scanner. METHODS: Ten healthy human participants and nine participants previously treated with radiotherapy were rotated within an MRI scanner. Participants' anxiety and motion sickness was assessed before being rotated in 45-degree increments and paused, representing a multi-field intensity-modulated radiotherapy treatment. An MR image was acquired at each 45-degree angle. Following imaging, anxiety and motion sickness were re-assessed, followed by a comfort questionnaire and exit interview. The significance of the differences in anxiety and motion sickness pre- versus post-imaging was assessed using Wilcoxon signed-rank tests. Content analysis was performed on exit interview transcripts. RESULTS: Eight of ten healthy and eight of nine patient participants completed the imaging session. Mean anxiety scores before and after imaging were 7.9/100 and 11.8/100, respectively (P = 0.26), and mean motion sickness scores were 5.3/100 and 13.7/100, respectively (P = 0.02). Most participants indicated likely acceptance of rotation if MRI were to be used in a hypothetical treatment. Physical discomfort was reported to be the biggest concern. CONCLUSIONS: Horizontal rotation within an MRI scanner was acceptable for most (17/19) participants.
Assuntos
Imageamento por Ressonância Magnética , Humanos , Imagens de Fantasmas , Planejamento da Radioterapia Assistida por Computador , Radioterapia de Intensidade Modulada , RotaçãoRESUMO
This paper describes the imaging performance of a high-field in-line MRI linear accelerator with a patient rotation system in-situ. Signal quality was quantified using signal-to-noise ratio (SNR) and RF uniformity maps. B0-field inhomogeneity was assessed using magnetic field mapping. SNR was evaluated with various entries into the Faraday cage which were required for extended couch translations. SNR varied between 103 and 87 across PRS rotation angles. Maximum B0-field inhomogeneity corresponded to 0.7 mm of geometric distortion. A 45 × 55 cm2 aperture allowed PRS translation with no reduction in SNR. Imaging performance with the PRS in-situ was found to be acceptable.