Medical physics最新文献

{"title":"Optimization of x-ray dark-field CT for human-scale lung imaging","authors":"Peiyuan Guo,&nbsp;Simon Spindler,&nbsp;Michal Rawlik,&nbsp;Jincheng Lu,&nbsp;Longchao Men,&nbsp;Mingzhi Hong,&nbsp;Marco Stampanoni,&nbsp;Hongxia Yin,&nbsp;Yan Xu,&nbsp;Zhenchang Wang,&nbsp;Li Zhang,&nbsp;Zhentian Wang","doi":"10.1002/mp.17630","DOIUrl":"10.1002/mp.17630","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Background</h3>\u0000 \u0000 <p>X-ray grating-based dark-field imaging can sense the small angle scattering caused by object's micro-structures. This technique is sensitive to the porous microstructure of lung alveoli and has the potential to detect lung diseases at an early stage. Up to now, a human-scale dark-field CT (DF-CT) prototype has been built for lung imaging.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>This study aimed to develop a thorough optimization method for human-scale dark-field lung CT and guide the system design.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>We introduced a task-based metric formulated as the contrast-to-noise ratio (CNR) between normal and lesioned alveoli for system parameter optimization and designed a digital human-thorax phantom to fit the task of lung disease detection. Furthermore, a computational framework was developed to model the signal propagation in DF-CT and established the link between system parameters and the CNR metric.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>We showed that for a DF-CT system, its CNR first increases and then decreases with the system auto-correlation length (ACL). The optimal ACL is mostly independent of system's visibility, and is only related to the phantom's properties, that is, its size and absorption. For our phantom, the optimal ACL is about 0.35 µm at the design energy of 60 keV. As for system geometry, increasing source-detector and isocenter-detector distance can extend the system's maximal ACL, making it easier for the system to meet the optimal ACL and relaxing the grating pitches. We proposed a set of parameters for a projective fringe system that can satisfy the simulated optimal ACL.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>This study introduced a task-based metric and a process for DF-CT optimization. We demonstrated that for a given phantom, the detection performance of the system is optimized at a specific ACL. The optimization method and design principles are independent from the underlying dark-field imaging method and can be applied to DF-CT system design using different grating-based implementations such as Talbot-Lau interferometer (TLI) or projective fringe method.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2155-2166"},"PeriodicalIF":3.2,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143054699","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deep learning-based Monte Carlo dose prediction for heavy-ion online adaptive radiotherapy and fast quality assurance: A feasibility study","authors":"Rui He,&nbsp;Jian Wang,&nbsp;Wei Wu,&nbsp;Hui Zhang,&nbsp;Yinuo Liu,&nbsp;Ying Luo,&nbsp;Xinyang Zhang,&nbsp;Yuanyuan Ma,&nbsp;Xinguo Liu,&nbsp;Yazhou Li,&nbsp;Haibo Peng,&nbsp;Pengbo He,&nbsp;Qiang Li","doi":"10.1002/mp.17628","DOIUrl":"10.1002/mp.17628","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Background</h3>\u0000 \u0000 <p>Online adaptive radiotherapy (OART) and rapid quality assurance (QA) are essential for effective heavy ion therapy (HIT). However, there is a shortage of deep learning (DL) models and workflows for predicting Monte Carlo (MC) doses in such treatments.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>This study seeks to address this gap by developing a DL model for independent MC dose (MCDose) prediction, aiming to facilitate OART and rapid QA implementation for HIT.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods and Materials</h3>\u0000 \u0000 <p>A MC dose prediction DL model called CAM-CHD U-Net for HIT was introduced, based on the GATE/Geant4 MC simulation platform. The proposed model improved upon the original CHD U-Net by adding a Channel Attention Mechanism (CAM). Two experiments were conducted, one with CHD U-Net (Experiment 1) and another with CAM-CHD U-Net (Experiment 2), and involved data from 120 head and neck cancer patients. Using patient CT images, three-dimensional energy matrices, and ray-masks as inputs, the model completed the entire MC dose prediction process within a few seconds.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>In Experiment 2, within the Planned Target Volume (PTV) region, the average gamma passing rate (3%/3 mm) between the predicted dose and true MC dose reached 99.31%, and 96.48% across all body voxels. Experiment 2 demonstrated a 46.15% reduction in the mean absolute difference in <span></span><math>\u0000 <semantics>\u0000 <msub>\u0000 <mi>D</mi>\u0000 <mn>5</mn>\u0000 </msub>\u0000 <annotation>${D_5}$</annotation>\u0000 </semantics></math> in organs at risk compared to Experiment 1.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>By extracting relevant parameters of radiotherapy plans, the CAM-CHD U-Net model can directly and accurately predict independent MC dose, and has a high gamma passing rate with the ground truth dose (the dose obtained after a complete MC simulation). Our workflow enables the implementation of heavy ion OART, and the predicted MCDose can be used for rapid QA of HIT.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2570-2580"},"PeriodicalIF":3.2,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143054569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Attix free-air chamber correction factors computed using EGSnrc","authors":"John T. Stasko,&nbsp;Wesley S. Culberson","doi":"10.1002/mp.17629","DOIUrl":"10.1002/mp.17629","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Background</h3>\u0000 \u0000 <p>A cylindrical free-air chamber, the Attix FAC, is used for absolute air-kerma measurements of low-energy photon beams at the University of Wisconsin Medical Radiation Research Center. Correction factors for air-kerma measurements of specific beams were determined in the 1990s. In order to measure air-kerma rates of beams in development, new correction factors must be computed.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>We aimed to compute monoenergetic correction factors for air-kerma measurements with the Attix FAC that could be used to determine corrections for arbitrary polyenergetic beams.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>A model of the Attix FAC was created in the Monte Carlo code, EGSnrc. The EGSnrc user codes, egs_fac, and egs_chamber, were utilized to calculate aperture transmission, scatter, collecting rod electron loss, and wall electron loss correction factors for incident monoenergetic photon beams with energies between 5 and 50 keV. Beam-specific correction factors were then derived from the monoenergetic correction factors and compared with the currently accepted values.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>Correction factors were computed in 0.5 keV intervals. The newly calculated beam-specific correction factors and the old conventional values agreed within 0.1% for all beams investigated.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusions</h3>\u0000 \u0000 <p>The process for determining monoenergetic correction factors for air-kerma measurements with a free-air chamber is detailed in this work. Beam-specific correction factors can then be calculated if photon spectra are known. This process can be carried out for any free-air chamber, given specific materials and dimensions for modeling.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"1991-1996"},"PeriodicalIF":3.2,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/mp.17629","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143049286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Overcoming the thermal limits of photon counting CT resolution using focal spot multiplexing: A feasibility study","authors":"Scott S. Hsieh","doi":"10.1002/mp.17631","DOIUrl":"10.1002/mp.17631","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Background&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;The spatial resolution of new, photon counting detector (PCD) CT scanners is limited by the size of the focal spot. Smaller, brighter focal spots would melt the tungsten focal track of a conventional X-ray source.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Purpose&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;To propose focal spot multiplexing (FSM), an architecture to improve the power of small focal spots and thereby enable higher resolution clinical PCD CT. In FSM, the source rapidly alternates between multiple focal spot locations. The dwell time at each focal spot location is much shorter than the readout interval of the PCD, and each location is visited many times during the readout interval so that heat can be effectively distributed over a larger surface area. The PCD accumulates recorded events on the detector (prior to slip ring transmission) into multiple &lt;i&gt;spatial bins&lt;/i&gt;, as a second dimension to conventional energy bins.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Methods&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;We estimated the maximum power permissible for a square, 0.2 mm focal spot assuming a maximum allowed surface temperature of 2900 K and a maximum transient temperature increase at the focal spot of 1400 K. This was performed using two separate thermal simulation codes: first, a commercial finite element method (FEM) was used to estimate bulk heating; second, a custom solver linearizing the heat equation was used to estimate track heating. FSM was simulated assuming that focal spot locations lay on parallel focal tracks, that instantaneous switching between tracks was possible, and that the space charge limit was never reached. We assumed a focal track velocity of 100 m/s and a 1 mm tungsten focal track layer with TZM alloy backing. The tube power was constant over a 4 s acquisition period.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Results&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;Without FSM, the 0.2 mm focal spot could attain a maximum power output of 17 kW before reaching the thermal limit. FSM required a minimum switching frequency of 0.5 MHz to produce benefit. With two focal tracks and a switching frequency of 4 MHz, the power could be increased to 28 kW, and with eight focal tracks and a switching frequency of 16 MHz, the power could be increased to 98 kW. In all cases, the 1400 K transient increase thermal limit was reached before the 2900 K maximum surface temperature constraint. The relationship between maximum power, switching frequency, and number of focal tracks is discussed in relation to the underlying physics of heat transport.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Conclusions&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;Focal spot multiplexing is an architec","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2040-2051"},"PeriodicalIF":3.2,"publicationDate":"2025-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143049320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Breast radiation therapy fluence painting with multi-agent deep reinforcement learning","authors":"Yang Dongrong,&nbsp;Li Xinyi,&nbsp;Yoo Sua,&nbsp;Blitzblau Rachel,&nbsp;McDuff Susan,&nbsp;Stephens Sarah,&nbsp;Segars Paul,&nbsp;Wu Q Jackie,&nbsp;Sheng Yang","doi":"10.1002/mp.17615","DOIUrl":"10.1002/mp.17615","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Background&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;The electronic compensation (ECOMP) technique for breast radiation therapy provides excellent dose conformity and homogeneity. However, the manual fluence painting process presents a challenge for efficient clinical operation.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Purpose&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;To facilitate the clinical treatment planning automation of breast radiation therapy, we utilized reinforcement learning (RL) to develop an auto-planning tool that iteratively edits the fluence maps under the guidance of clinically relevant objectives.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Methods&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;With institutional review board (IRB) approval, 70 patients treated with 6MV tangential photon beams with ECOMP technique were retrospectively collected and included in this study (20/50 for training/testing). Each pixel in the fluence map was assigned a reinforcement learning agent to perform independent action. Beam-eye-view projected dose profiles were generated to form state information as the input of the RL network. By predicting the Q value, pixel-wise actions were selected to modify specific pixel value in the fluence maps to improve overall plan quality. After dose calculation, reward signal calculated from the variation of target coverage and dose homogeneity was fed back to the RL framework and used to update network parameters. The RL generated plans were evaluated with dose distribution and dosimetric endpoints (i.e., Breast PTV V90%, Breast PTV V95%, Breast PTV V105%, Lung V20 Gy, Heart V5 Gy, Dmax) and compared with clinical plans.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Results&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;The RL agent took around 90 s to generate a ECOMP treatment plan. The RL plans exhibited plan quality comparable to clinical plans in terms of isodose distribution and dosimetric endpoints. The mean Breast PTV V95%, Breast PTV V105% of RL plans are &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mn&gt;77.759&lt;/mn&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mo&gt;%&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mo&gt;(&lt;/mo&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mo&gt;±&lt;/mo&gt;\u0000 &lt;mn&gt;8.904&lt;/mn&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mspace&gt;&lt;/mspace&gt;\u0000 &lt;mo&gt;%&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mo&gt;)&lt;/mo&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt;$77.759{mathrm{ % }}( { pm 8.904{mathrm{ % }}} )$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; and &lt;span&gt;&lt;/","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2015-2024"},"PeriodicalIF":3.2,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143034929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Three-dimensional complementary breast ultrasound (3D CBUS): Improving 3D spatial resolution uniformity with orthogonal images","authors":"Claire Keun Sun Park,&nbsp;Amal Aziz,&nbsp;Tiana Trumpour,&nbsp;Jeffrey Scott Bax,&nbsp;David Tessier,&nbsp;Igor Gyacskov,&nbsp;Lori Gardi,&nbsp;Aaron Fenster","doi":"10.1002/mp.17626","DOIUrl":"10.1002/mp.17626","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Background&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;With increasing evidence supporting three-dimensional (3D) automated breast (AB) ultrasound (US) for supplemental screening of breast cancer in increased-risk populations, including those with dense breasts and in limited-resource settings, there is an interest in developing more robust, cost-effective, and high-resolution 3DUS imaging techniques. Compared with specialized ABUS systems, our previously developed point-of-care 3D ABUS system addresses these needs and is compatible with any conventional US transducer, which offers a cost-effective solution and improved availability in clinical practice. While conventional US transducers have high in-plane resolution (axial and lateral), their out-of-plane resolution is constrained by the poor intrinsic elevational US resolution. Consequently, any oblique view plane in an acquired 3DUS image will contain high in-plane and poor out-of-plane resolution components, diminishing spatial resolution uniformity and overall diagnostic utility.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Purpose&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;To develop and validate a novel 3D complementary breast ultrasound (CBUS) approach to improve 3DUS spatial resolution uniformity using a conventional US transducer by acquiring and generating orthogonal 3DUS images.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Methods&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;We previously developed a cost-effective, portable, dedicated 3D ABUS system consisting of a wearable base, a compression assembly, and a mechanically driven scanner for automated 3DUS image acquisition, compatible with any commercial linear US transducer. For this system, we have proposed 3D CBUS approach which involves acquiring and registering orthogonal 3DUS images (&lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;A&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;annotation&gt;${V}_A$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; and &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;V&lt;/mi&gt;\u0000 &lt;mi&gt;B&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;annotation&gt;${V}_B$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;) with an aim of overcoming the poor resolution uniformity in the scanning direction in 3D US images. The voxel intensity values in the 3D CBUS image are computed with a spherical-weighted algorithm from the original orthogonal 3DUS images. Experimental validation was performed with 2DUS frame densities of 2, 4, 6 frames mm&lt;sup&gt;−1&lt;/sup&gt; using an agar-based phantom with a speed of sound of 1540 ms&lt;sup&gt;−1&lt;/sup&gt; and an embedded nylon bead. Lateral and axial full-width at half-maximum (FWHM&lt;sub&gt;LAT&lt;/","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2438-2453"},"PeriodicalIF":3.2,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143026042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparative image quality and dosimetric performance of two generations of dedicated breast CT systems","authors":"Juan J. Pautasso,&nbsp;Camille D. E. Van Speybroeck,&nbsp;Koen Michielsen,&nbsp;Ioannis Sechopoulos","doi":"10.1002/mp.17623","DOIUrl":"10.1002/mp.17623","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <h3> Background</h3>\u0000 \u0000 <p>Dedicated breast computed tomography (bCT) systems offer detailed imaging for breast cancer diagnosis and treatment. As new bCT generations are developed, it is important to evaluate their imaging performance and dose efficiency to understand differences over previous models.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Purpose</h3>\u0000 \u0000 <p>To characterize the imaging performance and dose efficiency of a second-generation (GEN2) bCT system and compare them to those of a first-generation (GEN1) system.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Methods</h3>\u0000 \u0000 <p>The imaging performance was evaluated through key metrics: modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) in the projection domain. In the image domain, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and the visibility of calcifications were analyzed using a quality control (QC) phantom with masses and calcification clusters. Air kerma and tube output were measured and mean glandular dose (MGD) estimated for different phantom sizes for dosimetric characterization of the acquisition protocols set by the automatic exposure control (AEC).</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Results</h3>\u0000 \u0000 <p>GEN2 outperformed GEN1 at higher spatial frequencies, with 57% of the MTF observed at 1 cycles/mm compared to 43% for GEN1. For a 2 mm diameter mass, GEN2 showed 60% higher CNR and 63% higher SNR. However, for larger masses, GEN1 outperformed GEN2, with CNR and SNR values higher by 12% to 44% and 14% to 43%, respectively. GEN2 also achieves higher DQE across the frequency spectrum, with 45% at 1 cycle/mm, compared to GEN1's 20%. Regarding calcifications in the QC phantom, the 320 µm calcifications resulted in distinct full-width-at-half-maxima (FWHM ± SD), with 897 ± 58 µm for GEN1 and 811 ± 127 µm for GEN2, with a <i>p</i>-value of 0.19. For 290 µm calcifications, GEN1's FWHM was 866 ± 129 µm, while GEN2's was narrower at 665 ± 57 µm, with a <i>p</i>-value of 0.01. The tube output was higher for GEN1 (45.2 mGy/mAs) compared to GEN2 (31.5 mGy/mAs). Additionally, GEN2 resulted in 8% lower MGD values compared to GEN1.</p>\u0000 </section>\u0000 \u0000 <section>\u0000 \u0000 <h3> Conclusion</h3>\u0000 \u0000 <p>While GEN1 offers better CNR and SNR for larger masses, GEN2 provides superior resolution for calcifications, better MTF, improved DQE, and lower MGD at AEC-determined settings.</p>\u0000 </section>\u0000 </div>","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2191-2200"},"PeriodicalIF":3.2,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/mp.17623","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143019053","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"In vivo dosimetry for proton therapy: A Monte Carlo study of the Gadolinium spectral response throughout the course of treatment","authors":"Mariana Brás,&nbsp;Hugo Freitas,&nbsp;Patrícia Gonçalves,&nbsp;João Seco","doi":"10.1002/mp.17625","DOIUrl":"10.1002/mp.17625","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Background&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;In proton radiotherapy, the steep dose deposition profile near the end of the proton's track, the Bragg peak, ensures a more conformed deposition of dose to the tumor region when compared with conventional radiotherapy while reducing the probability of normal tissue complications. However, uncertainties, as in the proton range, patient geometry, and positioning pose challenges to the precise and secure delivery of the treatment plan (TP). In vivo range determination and dose distribution are pivotal for mitigation of uncertainties, opening the possibility to reduce uncertainty margins and for adaptation of the TP.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Purpose&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;This study aims to explore the feasibility of utilizing gadolinium (Gd), a highly used contrast agent in MRI, as a surrogate for in vivo dosimetry during the course of scanning proton therapy, tracking the delivery of a TP and the impact of uncertainties intra- and inter-fraction in the course of treatment.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Methods&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;Monte Carlo simulations (Geant4 11.1.1) were performed, where a Gd-filled volume was placed within a water phantom and underwent treatment with a scanning proton TP delivering 4 Gy. The secondary photons emitted upon proton-Gd interaction were recorded and assessed for various tumor displacements. The spectral response of Gd to each pencil beam irradiation is therefore used as a surrogate for dose measurements during treatment.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Results&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;Results show that the deposited dose at the target volume can be tracked for each TP scanning point by correlating it with the recorded Gd signal. The analyzed Gd spectral line corresponded to the characteristic X-ray &lt;span&gt;&lt;/span&gt;&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;msub&gt;\u0000 &lt;mi&gt;k&lt;/mi&gt;\u0000 &lt;mi&gt;α&lt;/mi&gt;\u0000 &lt;/msub&gt;\u0000 &lt;annotation&gt;$text{k}_alpha$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; line at 43 keV. Displacements from the planned geometry could be distinguished by observing changes in the Gd signal induced by each pencil beam. Moreover, the total 43 keV signal recorded subsequently to the full TP delivery reflected deviations from the planned integral dose to the target.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Conclusions&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;The study suggests that the spectral response of a Gd-based contrast agent can be used for i","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2412-2424"},"PeriodicalIF":3.2,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/mp.17625","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143019073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"AAPM Task Group Report 274: Fluence rate dosimetry for photodynamic therapy (PDT)","authors":"Timothy C. Zhu,&nbsp;Brian W. Pogue,&nbsp;Andreea Dimofte,&nbsp;Jarod C. Finlay,&nbsp;Lothar Lilge,&nbsp;Ulas Sunar,&nbsp;Charles B. Simone II,&nbsp;Robert L. P. van Veen","doi":"10.1002/mp.17613","DOIUrl":"10.1002/mp.17613","url":null,"abstract":"<p>Photodynamic therapy (PDT) is a treatment modality clinically approved for several oncologic indications, including esophageal and endobronchial cancers, precancerous conditions including Barrett's esophagus and actinic keratosis, and benign conditions like age-related macular degeneration. While it is currently clinically underused, PDT is an area of significant research interest. Because PDT relies on the absorption of light energy by intrinsic or administered absorbers, the dosimetric quantity of interest is the absorbed energy per unit mass of tissue, proportional to the fluence rate of light in tissue. It has been demonstrated that the fluence rate at the tissue surface may differ significantly from the incident irradiance of light because of multiple scattering and absorption, both of which may vary among patients and tissue types. This report will review the current state-of-the-art fluence rate dosimetry technology. It will describe the two types of detectors currently available for fluence rate measurement, scattering-tip and fluorescence-based detectors, and review their principles of operation. The report will recommend strategies to establish calibration and quality assurance procedures for clinical fluence rate dosimetry equipment, and it will establish guidelines for clinical implementation of fluence rate dosimetry.</p>","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 3","pages":"1354-1371"},"PeriodicalIF":3.2,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/mp.17613","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143018949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enhancing fine-tuning efficiency and design optimization of an eight-channel 3T transmit array via equivalent circuit modeling and Eigenmode analysis","authors":"Ehsan Kazemivalipour,&nbsp;Ergin Atalar","doi":"10.1002/mp.17612","DOIUrl":"10.1002/mp.17612","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Background&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;Radiofrequency (RF) transmit arrays play a crucial role in various MRI applications, offering enhanced field control and improved imaging capabilities. Designing and optimizing these arrays, particularly in high-field MRI settings, poses challenges related to coupling, resonance, and construction imperfections. Numerical electromagnetic simulation methods effectively aid in the initial design, but discrepancies between simulated and fabricated arrays often necessitate fine-tuning. Fine-tuning involves iteratively adjusting the array's lumped elements, a complex and time-consuming process that demands expertise and substantial experience. This process is particularly required for high-Q-factor arrays or those with decoupling circuitries, where the impact of construction variations and coupling between elements is more pronounced. In this context, our study introduces and validates an accelerated fine-tuning approach custom RF transmit arrays, leveraging the arrays equivalent circuit modeling and eigenmode analysis of the scattering (S) parameters.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Purpose&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;This study aims to streamline the fine-tuning process of lab-fabricated RF transmit arrays, specifically targeting an eight-channel degenerate birdcage coil designed for 3T MRI. The objective is to minimize the array's modal reflected power values and address challenges related to coupling and resonance.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Methods&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;An eight-channel 3T transmit array is designed and simulated, optimizing capacitor values via the co-simulation strategy and eigenmode analysis. The resulting values are used in constructing a prototype. Experimental measurements of the fabricated coil's &lt;b&gt;S&lt;/b&gt;-parameters and fitting them into an equivalent circuit model, enabling estimation of self/mutual-inductances and self/mutual-resistances of the fabricated coil. Capacitor adjustments in the equivalent circuit model minimize mismatches between experimental and simulated results.&lt;/p&gt;\u0000 &lt;/section&gt;\u0000 \u0000 &lt;section&gt;\u0000 \u0000 &lt;h3&gt; Results&lt;/h3&gt;\u0000 \u0000 &lt;p&gt;The simulated eight-channel array, optimized for minimal normalized reflected power, exhibits excellent tuning and matching and an acceptable level of decoupling (|&lt;i&gt;S&lt;sub&gt;nn&lt;/sub&gt;&lt;/i&gt;|≤-23 dB and |&lt;i&gt;S&lt;sub&gt;mn&lt;/sub&gt;&lt;/i&gt;|≤-11 dB). However, the fabricated array displays deviations, including resonances at different frequencies and increased reflections. The proposed fine-tuning approach yields an updated set of capacitor values, improving resonance frequencies and reducing reflections. The fine-tuned","PeriodicalId":18384,"journal":{"name":"Medical physics","volume":"52 4","pages":"2025-2039"},"PeriodicalIF":3.2,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/mp.17612","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143019069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}