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We present a comment on "Benefits of completing homework for students with different aptitudes in an introductory electricity and magnetism course", by F. J. Kontur, K. de La Harpe, and N. B. Terry PRST-PER 11, 010105 (2015). Our data show that the conclusions Kontur and coworkers draw from their data may not be generally applicable.

Aims: To develop a method of processing non-formalin fixed prostate specimens removed at radical prostatectomy to obtain fresh tissue for research and for correlating diagnostic and molecular results with preoperative imaging. Methods/Results: The method involves a prostate slicing apparatus comprising a tissue slicer with a series of juxtaposed planar stainless steel blades linked to a support, and a cradle adapted to grip the tissue sample and receive the blades. The fresh prostate gland is held in the cradle and the blades are moved through the cradle slits to produce multiple 4 mm slices of the gland in a plane perpendicular to its posterior surface. One of the resulting slices is preserved in RNAIaterTM. The areas comprising tumour and normal glands within this preserved slice can be identified by matching it to the haematoxylin and eosin stained sections of the adjacent slices that are formalin fixed and paraffin wax embedded. Intact RNA can be extracted from the identified tumour and normal glands within the RNAlater preserved slice. Preoperative imaging studies are acquired with the angulation of axial images chosen to be similar to the slicing axis, such that stained sections from the formalin fixed, paraffin wax embedded slices match their counterparts on imaging. Conclusions: A novel method of sampling fresh prostate removed at radical prostatectomy that allows tissue samples to be used both for diagnosis and molecular analysis is described. This method also allows the integration of preoperative imaging data with histopathological and molecular data obtained from the prostate tissue slices. [ABSTRACT FROM AUTHOR]

We analyze the reorientational dynamics of a polymer close to the glass transition. Via comparison of two-time and four-time correlation functions, obtained from multidimensional nuclear magnetic resonance13C echo experiments, we are particularly sensitive to the fluctuations within the heterogeneous distribution of mobilities. From variation of the experimental parameters we obtain a detailed picture of the interplay between jump and diffusion dynamics, including the different types of motional heterogeneities and the geometry of the system. [ABSTRACT FROM AUTHOR]

Purpose: Left ventricle (LV) regional myocardial displacement due to cardiac motion was assessed using cardiovascular magnetic resonance (CMR) cine images to establish region-specific margins for cardiac radioablation treatments., Methods: CMR breath-hold cine images and LV myocardial tissue contour points were analyzed for 200 subjects, including controls (n = 50) and heart failure (HF) patients with preserved ejection fraction (HFpEF, n = 50), mid-range ejection fraction (HFmrEF, n = 50), and reduced ejection fraction (HFrEF, n = 50). Contour points were divided into segments according to the 17-segment model. For each patient, contour point displacements were determined for the long-axis (all 17 segments) and short-axis (segments 1-12) directions. Mean overall, tangential (longitudinal or circumferential), and normal (radial) displacements were calculated for the 17 segments and for each segment level., Results: The greatest overall motion was observed in the control group-long axis: 4.5 ± 1.2 mm (segment 13 [apical anterior] epicardium) to 13.8 ± 3.0 mm (segment 6 [basal anterolateral] endocardium), short axis: 4.3 ± 0.8 mm (segment 9 [mid inferoseptal] epicardium) to 11.5 ± 2.3 mm (segment 1 [basal anterior] endocardium). HF patients exhibited lesser motion, with the smallest overall displacements observed in the HFrEF group-long axis: 4.3 ± 1.7 mm (segment 13 [apical anterior] epicardium) to 10.6 ± 3.4 mm (segment 6 [basal anterolateral] endocardium), short axis: 3.9 ± 1.3 mm (segment 8 [mid anteroseptal] epicardium) to 7.4 ± 2.8 mm (segment 1 [basal anterior] endocardium)., Conclusions: This analysis provides an estimate of epicardial and endocardial displacement for the 17 segments of the LV for patients with normal and impaired LV function. This reference data can be used to establish treatment planning margin guidelines for cardiac radioablation. Smaller margins may be used for patients with higher degree of impaired heart function, depending on the LV segment., (© 2024 The Authors. Journal of Applied Clinical Medical Physics is published by Wiley Periodicals, Inc. on behalf of The American Association of Physicists in Medicine.)

The purpose of this work is to develop a procedure for commissioning four-dimensional computed tomography (4DCT) algorithms for minimum target reconstruction size, to quantify the effect of anterior-posterior (AP) motion artifacts on known object reconstruction for periodic and irregular breathing patterns, and to provide treatment planning recommendations for target sizes below a minimum threshold. A mechanical platform enabled AP motion of a rod and lung phantom during 4DCT acquisition. Static, artifact-free scans of the phantoms were first acquired. AP sinusoidal and patient breathing motion was applied to obtain 4DCT images. 4DCT reconstruction artifacts were assessed by measuring the apparent width and angle of the rod. Comparison of known tumor diameters and volumes between the static image parameters with the 4DCT image sets was used to quantify the extent of AP reconstruction artifact and contour deformation. Examination of the rod width, under sinusoidal motion, found it was best represented during the inhale and exhale phases for all periods and ranges of motion. From the gradient phases, the apparent width of the rod decreased with increasing amplitude and decreasing period. The rod angle appeared larger on the reconstructed images due to the presence of motion artifact. The apparent diameters of the spherical tumors on the gradient phases were larger/equivalent than the true values in the AP/LR direction, respectively, while the exhale phase consistently displayed the spheres at the approximately correct diameter. The Eclipse calculated diameter matched closely with the true diameter on the exhale phase and was found to be larger on the inhale, MIP, and Avg scans. The procedure detailed here may be used during the acceptance and commissioning period of a computed tomography simulator or retroactively when implementing a SBRT program to determine the minimum target size that can be reliably reconstructed., (© 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Purpose: Ventricular tachycardia (VT) is a rapid, abnormal heart rhythm that can lead to sudden cardiac death. Current treatment options include antiarrhythmic drug therapy and catheter ablation, both of which have only modest efficacy and have potential complications. Cardiac radiosurgery has the potential to be a noninvasive and efficient treatment option for VT. Cardiac motion, however, must be accounted for to ensure accurate dose delivery to the target region. Cardiac synchronized volumetric modulated arc therapy (CSVMAT) aims to minimize the dose delivered to normal tissues by synchronizing beam delivery with a cardiac signal, irradiating only during the quiescent intervals of the cardiac cycle (when heart motion is minimal) and adjusting the beam delivery speed in response to heart rate changes., Methods: A CSVMAT plan was adapted from a conventional VMAT plan and delivered on a Varian TrueBeam linear accelerator. The original VMAT plan was divided into three interleaved CSVMAT phases, each consisting of alternating beam-on and beam-off segments synchronized to a sample heart rate. Trajectory log files were collected for the original VMAT and CSVMAT deliveries and the dose distributions were measured with Gafchromic EBT-XD film., Results: Analysis of the trajectory log files showed successful synchronization with the sample cardiac signal. Film analysis comparing the original VMAT and CSVMAT dose distributions returned a gamma passing rate of 99.14% (2%/2 mm tolerance)., Conclusions: The film results indicated excellent agreement between the dose distributions of the original and cardiac synchronized beam deliveries. This study demonstrates a proof of principle cardiac synchronization strategy for precise radiation treatment plan delivery and adjustment to a variable heart rate. The cardiac synchronized technique may be advantageous in radioablation for VT., (© 2020 American Association of Physicists in Medicine.)

Purpose: To develop a novel quality assurance (QA) program to determine the air kerma strength (AKS) of brachytherapy seeds within preloaded needles using autoradiographs alone, without jeopardizing sterility or necessitating procedural changes either by the vendor or in the operating room., Methods and Materials: Digital autoradiographs of QA seed orders and sterile preloaded needles were acquired. Regions of interest of each preloaded seed were determined through an iterative scanning process identifying changes from background levels to radioactivity exposure. Average exposure values through the center of each region of interest were fitted with a Gaussian curve and Full Width at Half Maximums (FWHMs) were calculated. The two-dimensional exposure-scaled FWHM (Exp 2D ) measurements for the QA seed orders were plotted against measured AKS values and related using a linear curve fit that was adjusted using the third-party assay average AKS and applied as a calibration curve to convert Exp 2D to AKS., Results: Estimated seed AKS was found to have a strong dependence on position within the holding tray because of imager positioning inconsistencies. Calculated seed AKS for patient-specific seed orders using the curve scaling factor varied from the nominal order AKS by 1.1 ± 0.9% and from the third-party assay measurements by 0.0 ± 0.4%., Conclusions: This work depicts a clinically useful tool to aid in QA of preloaded brachytherapy permanent seed implant needles without compromising sterility or increasing clinical workloads. With this procedure, each individual seed's AKS can be verified automatically before a patient's scheduled implant or retroactively when auditing patient records., (Copyright © 2019 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: Xerostomia is one of the most likely late toxic effects of radiotherapy treatment in patients with head-and-neck cancers. Modern treatment techniques can incorporate knowledge of complication risk into treatment plans. To this end, the authors attempt to quantify the regional radiotherapy dose-dependence of salivary output loss and recovery in a prospective study., Methods: Salivary output was collected from patients undergoing radiotherapy treatment for head-and-neck cancers at the BC Cancer Agency between February 2008 and May 2013. Regional dose-dependence (i.e., dose susceptibility) of loss and recovery is quantified using nonparametric (Spearman's rank correlation coefficients, local linear regression) and parametric (least-sum of squares, least-median of squares) techniques., Results: Salivary flow recovery was seen in 79 of 102 patients considered (p < 0.0001, Wilcoxon sign rank test). Output loss was strongly correlated with left- and right parotid combined dose φ = min (DL,  45 Gy) + min (DR,  45 Gy), and can be accurately predicted. Median early loss (three months) was 72% of baseline, while median overall loss (1 yr) was 56% of baseline. Fitting an exponential model to whole parotid yields dose sensitivities A3m = 0.0604 Gy(-1) and A1y = 0.0379 Gy(-1). Recovery was not significantly associated with dose. Hints of lateral organ sub-segment dose-response dimorphism were observed., Conclusions: Sub-segmentation appears to predict neither loss nor recovery with any greater precision than whole parotid mean dose, though it is not any worse. Sparing the parotid to a combined dose φ of <50 Gy is recommended for a patient to keep ≈40% of baseline function and thus avoid severe xerostomia at 12 months post-treatment. It seems unlikely that a population's mean recovery will exceed 20%-30% of baseline output at 1 yr after radiotherapy treatment using current (whole-organ based) clinical guidelines.

Purpose: To develop a device for sectioning prostatectomy specimens that would facilitate comparison between histology and in vivo MRI., Materials and Methods: A multi-bladed cutting device was developed, which consists of an adjustable box capable of accommodating a prostatectomy specimen up to 85 mm in size in the lateral direction, a "plunger" tool to press on the excised gland from the top to prevent it from rolling or sliding during sectioning, and a multi-bladed knife assembly capable of holding up to 21 blades at 4-mm intervals. The device was tested on a formalin fixed piece of meat and subsequently used to section a prostatectomy specimen. Histology sections were compared with T2-weighted MR images acquired in vivo before the prostatectomy procedure., Results: The prostatectomy specimen slices were very uniform in thickness with each face parallel to the other with no visible sawing marks on the sections by the blades after the cut. MRI and histology comparison showed good correspondence between the two images., Conclusion: The developed device allows sectioning of prostatectomy specimens into parallel cuts at a specific orientation and fixed intervals. Such a device is useful in facilitating accurate correlation between histology and MRI data.

The purpose of this study was to evaluate distortion-corrected MRI as a radiotherapy planning tool for prostate cancer and the resultant implications for dose sparing of organs at risk. 11 men who were to be treated with radical conformal radiotherapy for localized prostate cancer had an MRI scan under radiotherapy planning conditions, which was corrected for geometric distortion. Radiotherapy plans were created for planning target volumes derived from the MRI- and CT-defined prostate. Dose volume histograms were produced for the rectum, bladder and penile bulb. The mean volume of the prostate as defined on CT and MRI was 41 cm3 and 36 cm3, respectively (p = 0.009). The predicted percentage of the rectum treated to dose levels of 45-65 Gy was significantly lower for plans delineating the prostate with MRI than for those with CT. The rectal-sparing effect was confined to the lowermost 4 cm of the rectum (anal canal). There were no differences between the predicted doses to bladder or penile bulb (as defined using MRI) between plans. In conclusion, prostate radiotherapy planning based on distortion-corrected MRI is feasible and results in a smaller target volume than does CT. This leads to a lower predicted proportion of the rectum, in particular the lower rectum (anal canal), treated to a given dose than with CT.