Browsing by Author "Arbab, Mona"

Now showing 1 - 6 of 6
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    The Dosimetric Outcome of a Rotational Planning Target Volume in Patients With Oropharyngeal Cancers
    (Springer, 2022-08) Arbab, Mona; Bartlett, Gregory; Dawson, Benjamin; Ge, Jeffrey; Langer, Mark; Radiation Oncology, School of Medicine
    An isotropic expanded Planning Target Volume (PTV) neglects patient's off-axis rotation. This study designs a rotational PTV that is used instead of the standard 3-mm Clinical Target Volume (CTV) expanded PTV in oropharyngeal cancers with the goal to reduce pharyngeal constrictor muscle (PCM) mean dose. 10 patients were retrospectively evaluated. For off-axis rotation, the image was rotated around the longitudinal axis (cervical spinal canal) ± 5 degrees. These new CTVs were combined to form the rotational PTV. The standard and rotational treatment plans were designed with the goal to keep the superior and middle PCM-CTV70 mean dose to less than 50 Gy. There were a 355 cGy reduction in the superior PCM mean dose (form 5332 to 4977 cGy) and a 506 cGy reduction in middle PCM mean dose (from 4185 to 3679 cGy). 60% of patients may have at least a 20% reduction in dysphagia probability based on a Normal Tissue Complication Probability (NTCP) formula. The superior and middle PCM mean dose were reduced to less than 50 Gy in 40 and 20% of cases. There was an association between superior PCM mean dose and overlap volume of PTV70 and superior PCM in both standard (r = 0.92, p = 0.001) and rotational (r = 0.84, p = 0.002) plans. This association was present for middle PCM and PTV70 (r = 0.52, p = 0.02 and r = 0.62, p = 0.006). Rotational PTV can lower the mean dose to superior and middle PCMs, ultimately leading to lower dysphagia rates.
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    Integrating Radiation Oncology Into Undergraduate Medical Education
    (Elsevier, 2021-07-28) Arbab, Mona; Holmes, Jordan A.; Olivier, Kenneth R.; Fields, Emma C.; Corbin, Kimberly S.; Kahn, Jenna M.; Zellars, Richard C.; Haywood, Antwione M.; Radiation Oncology, School of Medicine
    Cancer is one of the most important public health problems. However, medical education has not advanced at the same rate when it comes to cancer education. Currently, the United States Medical Licensing Examination subject examinations do not cover radiation oncology, prevention, and survivorship planning in its assessment model. Incorporating medical oncology and radiation oncology training into the undergraduate medical education curriculum can have a significant benefit in training future physicians. In this paper, we review current literature and propose some ideas that can help incorporate oncology, and specifically radiation oncology, into undergraduate medical education.
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    On the Computation of Mean and Variance of Spatial Displacements
    (ASME, 2024) Ge, Qiaode Jeffrey; Yu, Zihan; Arbab, Mona; Langer, Mark P.; Radiation Oncology, School of Medicine
    This paper studies the problem of computing an average (or mean) displacement from a set of given spatial displacements using three types of parametric representations: Euler angles and translation vectors, unit quaternions and translation vectors, and dual quaternions. It is shown that the use of Euclidean norm in the space of unit quaternions reduces the problem to that of computing the mean for each quaternion component separately and independently. While the resulting algorithm is simple, a change in the sign of a unit quaternion could lead to an incorrect result. A novel kinematic measure based on dual quaternions is introduced to capture the separation between two spatial displacements. This kinematic measure is used to define the variance of a set of displacements, which is then used to formulate a constrained least squares minimization problem. It is shown that the problem decomposes into that of finding the optimal translation vector and the optimal unit quaternion. The former is simply the centroid of the set of translation vectors and the latter is obtained as the eigenvector corresponding to the least eigenvalue of a 4 × 4 positive definite symmetric matrix. In addition, it is found that the weight factor used in combining rotations and translations in the formulation does not play a role in the final outcome. Examples are provided to show the comparisons of these methods.
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    On the Computation of the Average of Spatial Displacements
    (ASME, 2022) Ge, Q. J.; Yu, Zihan; Arbab, Mona; Langer, Mark; Radiation Oncology, School of Medicine
    Many applications in biomechanics and medical imaging call for the analysis of the kinematic errors in a group of patients statistically using the average displacement and the standard deviations from the average. This paper studies the problem of computing the average displacement from a set of given spatial displacements using three types of parametric representations: Euler angles and translation vectors, unit quaternions and translation vectors, and dual quaternions. It has been shown that the use of Euclidean norm in the space of unit quaternions reduces the problem to that of computing the average for each quaternion component separately and independently. While the resulting algorithm is simple, the change of the sign of a unit quaternion could lead to an incorrect result. A novel kinematic measure based on dual quaternions is introduced to capture the separation between two spatial displacement. This kinematic measure is then used to formulate a constrained least squares minimization problem. It has been shown that the problem decomposes into that of finding the optimal translation vector and the optimal unit quaternion. The former is simply the centroid of the set of given translation vectors and the latter can be obtained as the eigenvector corresponding to the least eigenvalue of a 4 × 4 positive definite symmetric matrix. It is found that the weight factor used in combining rotations and translations in the formulation does not play a role in the final outcome. Examples are provided to show the comparisons of these methods.
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    On the Construction of Confidence Regions for Uncertain Planar Displacements
    (ASME, 2024) Yu, Zihan; Ge, Qiaode Jeffrey; Langer, Mark P.; Arbab, Mona; Radiation Oncology, School of Medicine
    This paper studies the statistical concept of confidence region for a set of uncertain planar displacements with a certain level of confidence or probabilities. Three different representations of planar displacements are compared in this context and it is shown that the most commonly used representation based on the coordinates of the moving frame is the least effective. The other two methods, namely the exponential coordinates and planar quaternions, are equally effective in capturing the group structure of SE(2). However, the former relies on the exponential map to parameterize an element of SE(2), while the latter uses a quadratic map, which is often more advantageous computationally. This paper focus on the use of planar quaternions to develop a method for computing the confidence region for a given set of uncertain planar displacements. Principal component analysis (PCA) is another tool used in our study to capture the dominant direction of movements. To demonstrate the effectiveness of our approach, we compare it to an existing method called rotational and translational confidence limit (RTCL). Our examples show that the planar quaternion formulation leads to a swept volume that is more compact and more effective than the RTCL method, especially in cases when off-axis rotation is present.
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    On the Construction of Kinematic Confidence Ellipsoids for Uncertain Spatial Displacements
    (Springer, 2023) Yu, Zihan; Ge, Qiaode Jeffrey; Langer, Mark P.; Arbab, Mona; Radiation Oncology, School of Medicine
    This paper deals with the problem of estimating confidence regions of a set of uncertain spatial displacements for a given level of confidence or probabilities. While a direct application of the commonly used statistic methods to the coordinates of the moving frame is straight-forward, it is also the least effective in that it grossly overestimate the confidence region. Based on the dual-quaternion representation, this paper introduces the notion of the kinematic confidence ellipsoids as an alternative to the existing method called rotation and translation confidence limit (RTCL). An example is provided to demonstrate how the kinematic confidence ellipsoids can be computed.