Joint Head and Neck Radiotherapy-MRI Development Cooperative, Travis Salzillo, M. Alex Dresner, Ashley Way, Kareem Wahid, Brigid McDonald, Sam Mulder, Mohamed Naser, Renjie He, Yao Ding, Alison Yoder, Sara Ahmed, Kelsey Corrigan, Gohar Manzar, Lauren Andring, Chelsea Pinnix, R. Jason Stafford, Abdallah S. Mohamed, John Christodouleas, Jihong Wang, Clifton David Fuller
PurposeTo improve segmentation accuracy in head and neck cancer (HNC) radiotherapy treatment planning for the 1.5T hybrid magnetic resonance imaging/linear accelerator (MR-Linac), three-dimensional (3D), T2-weighted, fat-suppressed magnetic resonance imaging sequences were developed and optimized.ApproachAfter initial testing, spectral attenuated inversion recovery (SPAIR) was chosen as the fat suppression technique. Five candidate SPAIR sequences and a nonsuppressed, T2-weighted sequence were acquired for five HNC patients using a 1.5T MR-Linac. MR physicists identified persistent artifacts in two of the SPAIR sequences, so the remaining three SPAIR sequences were further analyzed. The gross primary tumor volume, metastatic lymph nodes, parotid glands, and pterygoid muscles were delineated using five segmentors. A robust image quality analysis platform was developed to objectively score the SPAIR sequences on the basis of qualitative and quantitative metrics.ResultsSequences were analyzed for the signal-to-noise ratio and the contrast-to-noise ratio and compared with fat and muscle, conspicuity, pairwise distance metrics, and segmentor assessments. In this analysis, the nonsuppressed sequence was inferior to each of the SPAIR sequences for the primary tumor, lymph nodes, and parotid glands, but it was superior for the pterygoid muscles. The SPAIR sequence that received the highest combined score among the analysis categories was recommended to Unity MR-Linac users for HNC radiotherapy treatment planning.ConclusionsOur study led to two developments: an optimized, 3D, T2-weighted, fat-suppressed sequence that can be disseminated to Unity MR-Linac users and a robust image quality analysis pathway that can be used to objectively score SPAIR sequences and can be customized and generalized to any image quality optimization protocol. Improved segmentation accuracy with the proposed SPAIR sequence will potentially lead to improved treatment outcomes and reduced toxicity for patients by maximizing the target coverage and minimizing the radiation exposure of organs at risk.
Diana Lin, Kareem Wahid, Benjamin Nelms, Renjie He, Mohamed Naser, Simon Duke, Michael Sherer, John Christodouleas, Abdallah S. R. Mohamed, Michael Cislo, James Murphy, Clifton Fuller, Erin Gillespie
PurposeContouring Collaborative for Consensus in Radiation Oncology (C3RO) is a crowdsourced challenge engaging radiation oncologists across various expertise levels in segmentation. An obstacle to artificial intelligence (AI) development is the paucity of multiexpert datasets; consequently, we sought to characterize whether aggregate segmentations generated from multiple nonexperts could meet or exceed recognized expert agreement.ApproachParticipants who contoured ≥1 region of interest (ROI) for the breast, sarcoma, head and neck (H&N), gynecologic (GYN), or gastrointestinal (GI) cases were identified as a nonexpert or recognized expert. Cohort-specific ROIs were combined into single simultaneous truth and performance level estimation (STAPLE) consensus segmentations. STAPLEnonexpert ROIs were evaluated against STAPLEexpert contours using Dice similarity coefficient (DSC). The expert interobserver DSC (IODSCexpert) was calculated as an acceptability threshold between STAPLEnonexpert and STAPLEexpert. To determine the number of nonexperts required to match the IODSCexpert for each ROI, a single consensus contour was generated using variable numbers of nonexperts and then compared to the IODSCexpert.ResultsFor all cases, the DSC values for STAPLEnonexpert versus STAPLEexpert were higher than comparator expert IODSCexpert for most ROIs. The minimum number of nonexpert segmentations needed for a consensus ROI to achieve IODSCexpert acceptability criteria ranged between 2 and 4 for breast, 3 and 5 for sarcoma, 3 and 5 for H&N, 3 and 5 for GYN, and 3 for GI.ConclusionsMultiple nonexpert-generated consensus ROIs met or exceeded expert-derived acceptability thresholds. Five nonexperts could potentially generate consensus segmentations for most ROIs with performance approximating experts, suggesting nonexpert segmentations as feasible cost-effective AI inputs.
Treatment of hepatocellular carcinoma (HCC) with sorafenib, a multikinase inhibitor, results in decreased microvessel density associated with increased levels of tumor hypoxia. However, the response rate is relatively poor, and recently it has been shown that tumor hypoxia and perfusion have predictive correlations with HCC response to sorafenib. In this study, we have investigated the correlation of oxygen saturation (SO2) and perfusion, estimated using photoacoustic-ultrasonic (PAUS) imaging, to the sorafenib treatment response in an orthotopic rat model of HCC. Following spectroscopic photoacoustic (sPA) imaging, microbubble contrast was introduced and harmonic imaging data were acquired for perfusion measurements. An FEM-based fluence correction model based on the diffusion approximation with empirically estimated tissue surface fluence and an SNR-based thresholding approach have been developed and validated on ex vivo and in vivo rat data to estimate SO2 using sPA imaging. The SO2 estimate has been obtained by solving an iterative minimization problem and then thresholded based on a pixel-wise empirically estimated SNR mask. For the treated cohort, the results show that the change in SO2 during an oxygen challenge is positively correlated with disease progression, while it is negatively correlated for the untreated cohort. Additionally, perfusion was significantly decreased in the treated group compared to baseline pretreatment and untreated cohort measurements. The reduced treatment-mediated perfusion leads to lack of oxygen supply and thus reduced oxygen levels. This study shows the potential of PAUS estimation of SO2 and perfusion to monitor and predict HCC sorafenib treatment response, ultimately leading to improved future treatment.
An algorithm to solve the diffuse optical tomography (DOT) problem is described which uses the anatomical
information from x-ray CT images. These provide a priori information about the distribution of the optical properties
hence reducing the number of variables and permitting a unique solution to the ill-posed problem. The light fluence rate
at the boundary is written as a Taylor series expansion around an initial guess corresponding to an optically homogenous
object. The second order approximation is considered and the derivatives are calculated by direct methods. These are
used in an iterative algorithm to reconstruct the tissue optical properties. The reconstructed optical properties are then
used for bioluminescence tomography where a minimization problem is formed based on the L1 norm objective function
which uses normalized values for the light fluence rates and the corresponding Green's functions. Then an iterative
minimization solution shrinks the permissible regions where the sources are allowed by selecting points with higher
probability to contribute to the source distribution. Throughout this process the permissible region shrinks from the
entire object to just a few points. The optimum reconstructed bioluminescence distributions are chosen to be the results
of the iteration corresponding to the permissible region where the objective function has its global minimum. This
provides efficient BLT reconstruction algorithms without the need for a priori information about the bioluminescence
sources.
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