Proton therapy can benefit chordoma treatment due to its capability of delivering highly conformal doses to the target area. However, clinical observations show that poor outcomes have been correlated to patients with metallic implants due to artifact contaminated computed tomography (CT) images. This study proposes a deep learning (DL)-based metal artifact reduction (MAR) framework to unsupervisely combine DL and k-means clustering algorithm and to obtain artifact-reduced images to support clinical applications. The framework includes three modules: data preprocessing, DL, and machine learning (ML) modules. An in-house material-based CT simulator was developed to augment the artifact training datasets. The DL module can adopt an unsupervised model to alleviate the need for labeled training data, which increases the clinical applicability. The ML module is used to classify tissue types from implant-free images around the adjacent treatment site, and the results can be used to further correct metal artifacts from DL images. We hypothesize that the artifact-reduced images should have similar CT number distributions to the adjacent CT images without surgical implants at the same treatment site. The Kullback-Leibler divergence (KLD) is used to evaluate the dissimilarity between these two distributions. The results indicate that the proposed method is comparative to Siemens iMAR and the current clinical procedure and can generate images with smaller KLD values than the images obtained by only using a DL model. The proposed method has the potential to reduce the treatment reserved margin that can decrease the radiation dose to normal tissues and accelerate the treatment planning time by revealing clear tumor structures.
This work presents a learning-based method to synthesize dual energy CT (DECT) images from conventional single energy CT (SECT). The proposed method uses a residual attention generative adversarial network. Residual blocks with attention gates were used to force the model to focus on the difference between DECT maps and SECT images. To evaluate the accuracy of the method, we retrospectively investigated 20 headand-neck cancer patients with both DECT and SECT scans available. The high and low energy CT images acquired from DECT acted as learning targets in the training process for SECT datasets and were evaluated against results from the proposed method using a leave-one-out cross-validation strategy. The synthesized DECT images showed an average mean absolute error around 30 Hounsfield Unit (HU) across the wholebody volume. These results strongly indicate the high accuracy of synthesized DECT image by our machinelearning-based method.
Owing to poor characterization of implant and adjacent human tissues, the presence of metal implants has been shown to be a risk factor for clinical results for proton therapy. In this project we have developed a way of characterizing implant and human materials in terms of water-equivalent thicknesses (WET) and relative stopping power (RSP) using a novel proton counting detector. We tracked each proton using a fast spectral imaging camera AdvaPIX-TPX3 which operated in energy mode measures collected energy per-voxel to derive the deposited energy along the particle track across the voxelated sensor. We considered three scenarios: sampling of WET of a CIRS M701 Adult Phantom (CMAP) at different locations; measurements of energy perturbations in the CMAP implanted with metal rods; sampling of WET of a more complex spine phantom. WET and RSP information were extracted from energy spectra at position along the central axis by using the shift in the most probable energy (MPE) from the reference energy (either initial incident energy or energy without a metal implant). Measurements were compared to TOPAS simulation results. Measured WET of the CMAP ranged from 18.63 to 25.23 cm depending on the location of the sampling which agreed with TOPAS simulation results within 1.6%. The RSPs of metals from CMAP perturbation measurements were determined as 1.97, 2.98, and 5.44 for Al, Ti and CoCr, respectively, which agreed with TOPAS within 2.3%. RSPs for material composition of a more complex spine phantom yielded 1.096, 1.309 and 1.001 for Acrylic, PEEK and PVC, respectively. In summary, this work has shown a method to accurately characterize RSPs of metal and human materials of CMAP implanted with metals and a complex spine phantom. Using the data obtained by the proposed method, it may be possible to validate RSP maps provided by conventional photon computed tomography techniques. Owing to poor characterization of implant and adjacent human tissues, the presence of metal implants has been shown to be a risk factor for clinical results for proton therapy. In this project we have developed a way of characterizing implant and human materials in terms of water-equivalent thicknesses (WET) and relative stopping power (RSP) using a novel proton counting detector. We tracked each proton using a fast spectral imaging camera AdvaPIX-TPX3 which operated in energy mode measures collected energy per-voxel to derive the deposited energy along the particle track across the voxelated sensor. We considered three scenarios: sampling of WET of a CIRS M701 Adult Phantom (CMAP) at different locations; measurements of energy perturbations in the CMAP implanted with metal rods; sampling of WET of a more complex spine phantom. WET and RSP information were extracted from energy spectra at position along the central axis by using the shift in the most probable energy (MPE) from the reference energy (either initial incident energy or energy without a metal implant). Measurements were compared to TOPAS simulation results. Measured WET of the CMAP ranged from 18.63 to 25.23 cm depending on the location of the sampling which agreed with TOPAS simulation results within 1.6%. The RSPs of metals from CMAP perturbation measurements were determined as 1.97, 2.98, and 5.44 for Al, Ti and CoCr, respectively, which agreed with TOPAS within 2.3%. RSPs for material composition of a more complex spine phantom yielded 1.096, 1.309 and 1.001 for Acrylic, PEEK and PVC, respectively. In summary, this work has shown a method to accurately characterize RSPs of metal and human materials of CMAP implanted with metals and a complex spine phantom. Using the data obtained by the proposed method, it may be possible to validate RSP maps provided by conventional photon computed tomography techniques.
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