Medical physics最新文献

{"title":"A modified lethal-potentially lethal model for oxygen-mediated FLASH sparing in stem cell niches.","authors":"Sumin Zhou","doi":"10.1002/mp.70469","DOIUrl":"10.1002/mp.70469","url":null,"abstract":"<p><strong>Background: </strong>Ultra-high dose rate (FLASH) irradiation can reduce normal-tissue toxicity while preserving tumor control, but a mechanistic explanation consistent with classical radiobiology remains incomplete. In particular, oxygen-depletion arguments based solely on bulk tissue oxygenation can appear inconsistent with clinically relevant fraction sizes, motivating a DNA-target-level oxygen formulation.</p><p><strong>Purpose: </strong>To develop a theory-based mechanistic extension of the Lethal and Potentially Lethal (LPL) model that explains oxygen-mediated FLASH trends without prescribing dose rate-dependent radiosensitivity, and to identify the baseline nuclear oxygen window in which sparing is expected to be largest.</p><p><strong>Methods: </strong>We introduce an explicit Precursor Lesion population whose fate is governed by competing chemical restitution/repair versus oxygen-dependent fixation into potentially lethal and lethal lesion channels. Fixation kinetics are coupled to a time-varying nuclear oxygen tension, <math> <semantics><mrow><mi>p</mi> <msub><mi>O</mi> <mn>2</mn></msub> <mrow><mo>(</mo> <mi>t</mi> <mo>)</mo></mrow> </mrow> <annotation>$p{{O}_2}( t )$</annotation></semantics> </math> , which decreases via radiolytic depletion during irradiation and recovers toward a baseline via reduced-order reoxygenation kinetics. To address the oxygen paradox, we distinguish bulk vascular oxygenation from a lower effective DNA target-level oxygenation that may arise in regulated stem-cell niches because of niche hypoxia and intracellular oxygen consumption. Oxygen modulation is implemented through a mechanistic exponential OER formulation parameterized by an oxygen-fixation rate constant, while retaining classical LPL behavior in the conventional low-dose-rate limit.</p><p><strong>Results: </strong>The model predicts that oxygen-mediated FLASH sparing is largest when baseline nuclear oxygenation lies in an intermediate physiologic-hypoxia regime, corresponding to the steep oxygen-responsive portion of the OER curve. In the reference parameter set, a quiescent normal-tissue niche with baseline <math> <semantics><mrow><mi>p</mi> <msub><mi>O</mi> <mrow><mn>2</mn> <mo>,</mo> <mn>0</mn></mrow> </msub> </mrow> <annotation>$p{{O}_{2,0}}$</annotation></semantics> </math>  = 3 mmHg shows appreciable sparing under FLASH delivery, whereas sparing is minimal when the baseline lies near either the OER floor ( <math> <semantics><mrow><mi>p</mi> <msub><mi>O</mi> <mrow><mn>2</mn> <mo>,</mo> <mn>0</mn></mrow> </msub> </mrow> <annotation>$p{{O}_{2,0}}$</annotation></semantics> </math>  = 0.2 mmHg) or the OER saturation plateau ( <math> <semantics><mrow><mi>p</mi> <msub><mi>O</mi> <mrow><mn>2</mn> <mo>,</mo> <mn>0</mn></mrow> </msub> </mrow> <annotation>$p{{O}_{2,0}}$</annotation></semantics> </math>  = 30 mmHg). Sensitivity analyses preserve this intermediate oxygen window while shifting the magnitude and threshold of the effect.</p><p><str","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70469"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13158172/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147871067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Automated extraction of the plane of minimal hiatal dimensions and mid-sagittal plane from 3D transperineal ultrasound.","authors":"Zachary Szentimrey, Golafsoun Ameri, Christopher X Hong, R Y K Cheung, Ahmed Eltahawi, Eranga Ukwatta","doi":"10.1002/mp.70473","DOIUrl":"10.1002/mp.70473","url":null,"abstract":"<p><strong>Background: </strong>Transperineal ultrasound (TPUS) is a valuable imaging tool for evaluating patients with a variety of pelvic floor disorders, including pelvic organ prolapse (POP). Currently, calculating measurements of anatomical structures and relationships as well as extracting the mid-sagittal (MS) plane of 2D and 3D ultrasound images are obtained manually, which is a time-consuming process and requires a reviewer with prior training in pelvic floor US interpretation. The need for manual analysis of ultrasound images has limited the broader adoption of TPUS for evaluating pelvic floor disorders in both research and clinical practice. An automated segmentation and plane extraction method would improve the ability to easily quantify pelvic anatomy relevant to pelvic floor disorders and improve the efficiency and reproducibility of POP diagnosis and treatment.</p><p><strong>Purpose: </strong>To develop a fast, reproducible, and automated method of acquiring the MS plane, plane of minimal hiatal dimensions (PMHD), and segmentations of the pelvic floor organs from 3D TPUS images.</p><p><strong>Methods: </strong>Our method used a nnU-Net segmentation model to segment structures of interest in the 3D TPUS images. The model segmented the pubis symphysis (PS), urethra, bladder, rectum, rectal ampulla, and anorectal angle (ANA). The segmented output was then fed into a heuristics-based method to determine the PS and ANA to extract the MS plane and PMHD automatically. We used a dataset consisting of 161 3D TPUS images from 104 patients. 89 of the volumes were acquired in a resting state and 72 during the Valsalva maneuver. The segmentation and plane extraction algorithms were evaluated by comparing the results with manual segmentations and manual plane extraction methods using the dice similarity coefficients (DSC), mean absolute surface distance (MAD), and absolute angle difference (AAD), respectively. The Wilcoxon-signed rank statistical test was used with Bonferroni-correction to p < 0.01. Cohen effect size was used for comparing model results.</p><p><strong>Results: </strong>The nnU-Net segmentation model reported an average DSC(%) of 70.4%, 58.5%, 57.1%, 48.9%, 39.0%, and 19.8% for bladder, rectum, PS, urethra, ANA, and rectal ampulla respectively. The nnU-Net segmentation model achieved significantly higher DSC (p < 0.01) for the urethra and rectum than all other tested models. Across all metrics, the nnU-Net segmentation model achieved an average effect size of 0.3, 0.5, 0.7, and 0.8 compared to a 3D ResNet34 + U-Net, 3D U-Net, 2D U-Net, and Attention 3D U-Net model, respectively. The average AADs between the automatically calculated plane slices and manually estimated planes dataset for the MS plane and PMHD were 3.8° and 2.4°, respectively. The PS and ANA segmentation centroids were used to calculate the MS plane and PMHD and they had distance errors of 3.6 mm and 4.4 mm.</p><p><strong>Conclusions: </strong>We developed an automa","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70473"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13158169/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147871077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral deep learning-based patient and bowtie scatter correction for clinical photon-counting CT.","authors":"Lukas Hennemann, Julien Erath, Andreas Heinkele, Eric Fournié, Martin Petersilka, Karl Stierstorfer, Marc Kachelrieß","doi":"10.1002/mp.70442","DOIUrl":"10.1002/mp.70442","url":null,"abstract":"<p><strong>Background: </strong>The presence of scatter in computed tomography degrades image quality, and can be caused by the patient and by other components in the beam path, such as the bowtie filter. While conventional energy-integrating detectors do not provide spectral distinction, photon-counting (PC) detectors are energy-selective and provide spectral information about the incoming X-ray photons. Since each energy threshold is affected differently by scatter, this spectral information implicitly encodes the scatter content of a projection.</p><p><strong>Purpose: </strong>The purpose of this work is to investigate how the spectral information can be exploited to improve deep learning (DL)-based scatter correction. Furthermore, the performance of joint and separate patient and bowtie scatter correction will be investigated, addressing that bowtie scatter has not been considered in current DL-based approaches.</p><p><strong>Methods: </strong>We present a DL-based approach that can estimate bowtie and patient scatter jointly and compare it against a separate correction. We also introduce neural network-based methods that incorporate the spectral information inherent in PCCT for scatter correction. We present networks that estimate scatter for up to four energy thresholds simultaneously. Training and validation was performed with Monte Carlo data as well as with real data measured by a clinical PCCT system.</p><p><strong>Results: </strong>When comparing joint and separate patient and bowtie scatter estimation, both methods reduce the mean absolute error (MAE) from 8 HU to 1 HU. All proposed DSE methods effectively reduce scatter artifacts and perform better than the convolution-based reference approach. Incorporating the spectral information further improves the performance, with the DSE variant with four energy thresholds achieving the best overall results for all thresholds. For all energy thresholds tested, the spectral DSE methods reduced scatter errors originating from the patient and the bowtie in PCCT from up to 8 HU to below 1 HU. In addition to the global MAE, we report a critical MAE (MAE<sub>10</sub>) restricted to voxels with uncorrected errors <math><semantics><mo>></mo> <annotation>$>$</annotation></semantics> </math> 10 HU, as such deviations are visually perceptible in soft tissue and exceed the noise level of modern CT systems. In all test cases, the proposed spectral methods reduced the MAE<sub>10</sub> from 23.8 HU in the uncorrected images to 1.6 HU after spectral correction. The affected voxels comprised on average 25 % of the image volume, indicating a significant reduction in artifact intensity in the most affected areas. In virtual monoenergetic images (VMI), the application of spectral neural networks resulted in a significant reduction in MAE from <math><semantics><mo>∼</mo> <annotation>$sim$</annotation></semantics> </math> 16 HU to <math><semantics><mo>∼</mo> <annotation>$sim$</annotation></semantics> </math> 2 HU ","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70442"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13125421/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147793336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MRI-informed hypoxia-based proton radiotherapy dose escalation for head-and-neck cancer-a proof-of-concept.","authors":"Sebastian Tattenberg, Nils Tanneau, Walid Dandachly, Benjamin Leporq, Benoit Allignet, Charlène Bouyer, Frank Pilleul, Vincent Gregoire, Marie Claude Biston, Olivier Beuf","doi":"10.1002/mp.70480","DOIUrl":"10.1002/mp.70480","url":null,"abstract":"<p><strong>Background: </strong>Partially as a result of hypoxia-induced radioresistance, rates of treatment failure for head-and-neck cancer patients receiving radiotherapy can be considerable. Clinical trials utilizing positron emission tomography (PET) to image tumor hypoxia and escalate the prescription dose in hypoxic sub-volumes are being pursued in response, with current clinical prescription doses of 70 Gy generally escalated to 77-78 Gy. Instead utilizing magnetic resonance imaging (MRI) for hypoxia-based prescription dose escalation would be associated with a variety of advantages, including not requiring an additional imaging-related radiation dose to be delivered to the patient and allowing for a variety of other functional maps to be extracted from the same patient imaging session, in addition to tumor hypoxia information.</p><p><strong>Purpose: </strong>The purpose of this study is to investigate the benefits of MRI-informed hypoxia-based radiotherapy dose escalation for head-and-neck cancer patients treated with proton radiotherapy.</p><p><strong>Methods: </strong>Ten patients with head-and-neck cancer scheduled to undergo photon therapy underwent a multi-parametric MRI protocol based on which tumor hypoxia maps were computed for every patient using a quantitative blood oxygenation level dependent (BOLD) approach. Four proton therapy treatment plans were then created for each patient, consisting of intensity-modulated proton therapy (IMPT) and proton arc therapy (PAT) treatment planning performed according to current clinical standards (IMPT<sub>Conv</sub> and PAT<sub>Conv</sub>) or with a 10% prescription dose escalation to the hypoxic sub-volumes of the low- and high-risk target structures (IMPT<sub>Esc</sub> and PAT<sub>Esc</sub>). The generated treatment plans were then analyzed with respect to target and organ-at-risk (OAR) doses and normal tissue complication probabilities (NTCPs) as well as tumor control probabilities (TCPs) calculated according to conventional models (TCP<sub>Conv</sub>) or with consideration of hypoxia-induced radioresistance (TCP<sub>Hyp</sub>). Statistical significance (p < 0.05) of different TCP or mean OAR dose distributions was determined using the Wilcoxon signed-rank test.</p><p><strong>Results: </strong>During IMPT, radiotherapy prescription dose escalation increased TCP<sub>Conv</sub> in the nominal scenario by (5.9 ± 6.3) percentage points (pp) in the normoxic (p < 0.001) and (5.2 ± 9.0) pp in the hypoxic target volumes (p = 0.006). In the worst-case scenario, TCP<sub>Conv</sub> was increased by (5.6 ± 4.5) pp (p < 0.001) and (5.3 ± 6.4) pp (p = 0.003). Dose escalation during PAT improved TCP<sub>Conv</sub> by (3.1 ± 3.3) pp (p < 0.001) and (2.1 ± 5.4) pp (p = 0.015) in the nominal scenario and (3.3 ± 3.1) pp (p < 0.001) and (3.3 ± 4.4) pp (p < 0.001) in the worst-case scenario. When hypoxia-induced radioresistance was considered, dose escalation elevated TCP<sub>Hyp</sub> in the nominal scenario","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70480"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147936744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Incremental feature fusion based time series forecasting with cumulative risk constraint for longitudinal overall survival prediction.","authors":"Zhenyu Tang, Jingfeng Lin, Jiannan Li, Junjun Pan, Jing Yan","doi":"10.1002/mp.70495","DOIUrl":"10.1002/mp.70495","url":null,"abstract":"<p><strong>Background: </strong>Overall survival (OS) prediction methods usually adopt pre-operative data which lack important prognosis-related information, such as post-operative lesion status and evolution during treatment, leading to unsatisfactory performance. Incorporating longitudinal data into OS prediction, however, introduces two main challenges: (1) variable time span; and (2) implicit spatiotemporal information.</p><p><strong>Purpose: </strong>This study aims to break the limitation of pre-operative data based OS prediction by addressing the aforementioned two main challenges and leveraging longitudinal data to achieve accurate OS prediction.</p><p><strong>Methods: </strong>We propose a novel longitudinal data based OS prediction method. Specifically, a new incremental feature fusion (IFF) based time series forecasting module is presented to derive accumulated features up to each time point and fill missing time points in longitudinal data. It addresses the challenge of variable time span with high computational efficiency compared to the widely applied decoder-only transformer with causal-attention (DoT-CA). Based on the accumulated features in the IFF module, corresponding survival risks up to each time point are predicted under a cumulative survival risk (CSR) constraint, where the survival risks are encouraged to be monotonically increased over time, effectively exploring the spatiotemporal information.</p><p><strong>Results: </strong>In the experiment, both in-house and public multimodal MR datasets (BraTS2020) containing 1678 patients of diffuse glioma are used to evaluate our method, and the experimental results show that our method outperforms all state-of-the-art (SOTA) methods with statistical significance. Further ablation study shows that both proposed IFF module and CSR constraint are effective in longitudinal OS prediction. Moreover, the proposed IFF module is more efficient than DoT-CA, enabling scalable offline longitudinal analysis on large patient cohorts.</p><p><strong>Conclusion: </strong>Longitudinal data contain important spatiotemporal information related to prognosis, based on which more accurate OS prediction can be achieved comparing with existing pre-operative data based methods. For longitudinal data with variable time span, the evolution pattern of lesions can be effectively learned and used to fill up the missing time points. Codes of our method are available at https://github.com/BH-MICom/OSTimes.</p>","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70495"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147990405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Integrating measurement and simulation for evaluation of patient-specific whole-body dosimetry in clinical BNCT.","authors":"Ryo Kakino, Naonori Hu, Akinori Sasaki, Mai Nojiri, Yuki Yoshino, Satoshi Takeno, Teruhito Aihara, Nishiki Matsubayashi, Takushi Takata, Hiroki Tanaka, Keiji Nihei, Koji Ono","doi":"10.1002/mp.70474","DOIUrl":"10.1002/mp.70474","url":null,"abstract":"<p><strong>Background: </strong>Boron neutron capture therapy (BNCT) is a treatment modality that utilises high intensity neutron beam in combination with a boron drug to target cancer cells at the cellular level. Despite decades of research in this field, there are very few reports on out-of-field patient dose of BNCT.</p><p><strong>Purpose: </strong>To quantify patient whole-body out-of-field dose during clinical BNCT for recurrent head-and-neck cancer using an integrated measurement-simulation workflow.</p><p><strong>Methods: </strong>The data of 271 patients that received BNCT for recurrent head and neck were analyzed for this study.First, the neutron and gamma ray doses were measured using activation foils and thermoluminescent dosimeters, respectively. The detectors were placed onto the surface of the patient at various locations and the reaction rate of the metal foils were measured. Second, PHITS Monte Carlo simulation was performed to evaluate the neutron energy spectrum at each location and the corresponding neutron equivalent dose was determined. The total dose was calculated by summing the neutron equivalent dose and the gamma ray dose. The results were compared with other radiotherapy modalities.</p><p><strong>Results: </strong>The mean ± standard deviation of equivalent dose at neck, chest, abdomen, waist, knee, and ankle were calculated to be 1.93 ± 1.12, 0.71 ± 0.42, 0.23 ± 0.12, 0.11 ± 0.06, 0.05 ± 0.03, 0.02 ± 0.01 Gy-eq, respectively. Excluding the neck region, the gamma ray dose was dominant at all measurement points. From the abdomen below, dose from the primary gamma ray were dominant, indicating a potential for reducing the dose to these regions by installing additional lead shielding in the treatment room walls. In comparison to other radiotherapy modalities, out-of-field dose of BNCT was found to be similar.</p><p><strong>Conclusion: </strong>The whole-body dose for patients that received BNCT for recurrent head and neck cancer were estimated by scaling PHITS derived neutron dose using multifoil reaction rates and adding measured gamma dose. The results showed the out-of-field dose was comparable to other radiotherapy modalities and further added confidence that BNCT is a safe treatment modality.</p>","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70474"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13158168/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147871125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Clinical validation of a high-definition mid-position magnetic resonance imaging approach for lung radiotherapy planning.","authors":"Katrinus Keijnemans, Astrid L H M W van Lier, Pim T S Borman, Hilâl Tekatli, Jacquelien Pomp, Romy E van Weelderen, Bas W Raaymakers, Martin F Fast","doi":"10.1002/mp.70457","DOIUrl":"10.1002/mp.70457","url":null,"abstract":"&lt;p&gt;&lt;strong&gt;Background: &lt;/strong&gt;Respiratory-correlated four-dimensional (4D) magnetic resonance imaging (4D-MRI) is useful to estimate breathing induced motion for MRI-guided radiotherapy. Based on 4D-MR image sets, a three-dimensional mid-position (MidP) MRI can be generated using deformable image registration (DIR) for radiotherapy planning. However, the desired spatial resolution and image contrast of the MidP MRI may differ from the original 4D-MRI.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;This retrospective study validates a high-definition (HD)-MidP MRI approach that combines 4D-MRI motion information with a high-resolution MRI to enhance the spatial resolution of the MidP image.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Computed tomography (CT) and MR image sets of 25 lung cancer patients were eligible, of whom 17 were complete and suitable for analysis. Standard-definition (SD)-MidP images were derived by applying DIR to warp the ten respiratory phases of a 4D-CT or 4D-MRI, whereas the HD-MidP MRI was derived by warping a high-resolution respiratory-triggered MRI to the MidP. The MidP image quality was assessed with a 4-point Likert scale on tumor and organ at risk (OAR) distinctiveness by three readers. Additionally, the gross tumor volume (GTV) was delineated by the readers, from which a consensus contour was derived for each MidP image. Reader contours were evaluated using the Dice similarity coefficient (DSC) and mean distance to agreement (DTA). Anatomical accuracy was evaluated by comparing MidP tumor locations to manually determined tumor displacements, while DIR precision was analyzed using the distance to discordance metric (DDM). Moreover, deformation vector fields (DVFs) from the DIR were used to automatically calculate MidP-based treatment margins.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;Eighteen targets were identified in seventeen patients. All HD-MidP MR image sets were delineated, while 98% (53/54) of the SD-MidP CT and 87% (47/54) of the SD-MidP MR image sets were of adequate quality for delineation. The SD-MidP MRI was positively scored in 13 out of 47 assessments for tumor distinctiveness and in 6 out of 47 assessments for OAR distinctiveness. In contrast, the HD-MidP MRI showed a substantial improvement, with positive scores in 45 out of 54 assessments for tumor distinctiveness and 51 out of 54 assessments for OAR distinctiveness. Contour analyses revealed that the HD-MidP MRI achieved the highest average DSC value (0.83) and, simultaneously, the lowest mean DTA value (0.96 mm). Compared to the manually determined tumor displacements, subvoxel differences in MidP tumor location were observed in 96% (52/54) of the registrations. The distribution of DDM values (median: 1.1 mm) for the HD-MidP MRI was found to be significantly higher than the distributions for the SD-MidP CT (median: 0.2 mm) and SD-MidP MRI (median: 0.7 mm), indicating a lower, but still subvoxel, precision for the HD-MidP MRI approach. The DVF variability was higher for the HD-Mid","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70457"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13143559/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147848162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Performance evaluation of a clinical SPECT system with multifocal collimator for brain studies.","authors":"Tamaki Otani, Yamato Kunikane, Satoru Takashi, Shota Azane, Akihiko Fujita, Noritake Matsuda, Masafumi Amano","doi":"10.1002/mp.70451","DOIUrl":"10.1002/mp.70451","url":null,"abstract":"<p><strong>Background: </strong>Single-photon emission computed tomography (SPECT) is an indispensable examination for evaluating brain function to diagnose dementia. During head examination, the collimator makes contact with the shoulders, which often causes the patient discomfort. A new multifocal high-resolution collimator (SMARTZOOM high resolution and extended [SZHRX]) can maintain image quality, even when there is distance between the patient and the collimator. Therefore, it may be a useful tool to prevent patient discomfort during head imaging.</p><p><strong>Purpose: </strong>In this study, we evaluated spatial resolution, sensitivity, uniformity, and %contrast in several basic experiments using different phantoms to clarify the image quality of the multifocal collimator.</p><p><strong>Methods: </strong>We used ^99mTc and ¹²³I nuclides, which were sealed in several phantoms and imaged using SZHRX. The rotation radius for SZHRX was varied from 24-34.5 cm. For comparison, low-energy high-resolution (LEHR) and low-medium energy general purpose (LMEGP) images were acquired with a rotation radius of 14 cm. Spatial resolution, sensitivity, uniformity, and %contrast were calculated from the images obtained using each phantom and collimator.</p><p><strong>Results: </strong>For both ^99mTc and ¹²³I, the wider the radius of rotation, the larger the full-width half maximum (FWHM) of SZHRX. The FWHM of SZHRX was larger than that of LEHR, and the FWHM of SZHRX was smaller than that of LMEGP. The sensitivity of SZHRX increased as the distance increased, regardless of nuclides. For ^99mTc, SZHRX had higher sensitivity than LEHR. The sensitivity of SZHRX for ¹²³I was lower than that of LMEGP at short distances, with the same sensitivity at a radius of rotation of 26-28 cm. The coefficient of variation (CV) of ^99mTc for SZHRX was lower than that for LEHR, and the further the distance, the lower the CV. For ¹²³I, the CVs of SZHRX and LMEGP were comparable. The %contrast of SZHRX worsened as the rotation radius increased. For ^99mTc, the %contrast of SZHRX was lower than that of LEHR. For ¹²³I, the %contrast of SZHRX and LMEGP were comparable.</p><p><strong>Conclusions: </strong>It is possible to acquire images with high spatial resolution and uniformity, even if the rotation radius is widened by the use of SZHRX. The image quality of SZHRX obtained in this study will be helpful for future clinical applications.</p>","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70451"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13107236/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147793349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Applying a portable pocket handheld ultrasound scanner to monitor tumor volume in preclinical studies.","authors":"Stavros Melemenidis, Luis A Soto, Ahmed Nagy El Kaffas, Ramish M Ashraf, Billy W Loo, Edward E Graves","doi":"10.1002/mp.70462","DOIUrl":"10.1002/mp.70462","url":null,"abstract":"<p><strong>Background: </strong>Calipers remain the most common method for monitoring tumor volume in preclinical studies, despite known geometric limitations that can lead to substantial measurement error, particularly for irregularly shaped tumors. Portable handheld ultrasound (US) devices have recently become more accessible and may provide a practical alternative; however, their quantitative performance in routine small-animal workflows has not been fully characterized.</p><p><strong>Purpose: </strong>To evaluate whether a low-cost handheld US probe is suitable for routine preclinical tumor-volume measurement and to quantify its accuracy relative to calipers using cone-beam computed tomography (CBCT)-derived volumes as the reference standard.</p><p><strong>Methods: </strong>Five BALB/c and five C57BL/6J mice (n = 10) bearing subcutaneous CT26 (colorectal) or LLC1 (lung) tumors were measured on day 14 post-inoculation using digital calipers and a handheld US probe. Tumor volumes were estimated using caliper-derived length × width (L×W_Cal), US-derived length × width (L×W_US), US-derived length × width × depth (L×W×D_US), and an US-based region-of-interest method (ROI_US). Excised tumors were imaged with CBCT and segmented to obtain reference volumes. Volumes were normalized to CBCT and analyzed using nonparametric repeated-measures statistics (Friedman test with Holm-Bonferroni-corrected Wilcoxon signed-rank tests; significance defined as adjusted p < 0.05). Effect sizes were calculated using the rank-biserial correlation coefficient.</p><p><strong>Results: </strong>CBCT tumor volumes ranged from 30-170 mm³ (82.8 ± 49.6 mm³). Caliper-derived L×W_Cal volumes significantly overestimated CBCT (median 196% of reference; adjusted p = 0.0078; large effect size, r_rb = 1.0). US-based methods demonstrated substantially reduced bias and variability. L×W_US, L×W×D_US, and ROI_US volumes were not significantly different from CBCT after correction, with ROI_US showing the lowest median absolute error (9.6%).</p><p><strong>Conclusions: </strong>In this preclinical cohort, handheld US reduced systematic volumetric overestimation relative to calipers and demonstrated improved agreement with CBCT-derived reference volumes. ROI-based US analysis yielded the lowest absolute error. These findings support the use of portable US as a more accurate alternative to calipers for tumor-volume monitoring in small-animal studies.</p>","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70462"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13360284/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147936700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An extended photon isoeffective dose model accounting for the energy-dependent effectiveness of secondary charged particles in BNCT.","authors":"Ana Mailén Dattoli Viegas, Sebastián Gossio, Jessica Riback, Lucrecia Mariel Valeriano, Gustavo Santa Cruz, Alice Casali, Mario Pietro Carante, Francesca Ballarini, Setareh Fatemi, Ian Postuma, Valerio Vercesi, Silva Bortolussi, Ricardo Luis Ramos, Sara Josefina González","doi":"10.1002/mp.70410","DOIUrl":"10.1002/mp.70410","url":null,"abstract":"&lt;p&gt;&lt;strong&gt;Background: &lt;/strong&gt;The absorbed dose in Boron Neutron Capture Therapy (BNCT) arises from various radiation components, each contributing differently to the overall biological effect. These effects depend not only on the absorbed dose but also on the type and energy of the involved secondary charged particles. Current dosimetric models convert absorbed dose into an equivalent photon dose using radiation-specific weighting factors that account for some differences in radiation type. However, these models generally neglect the energy dependence of biological effectiveness.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;To evaluate the relevance of incorporating the energy dependence of secondary charged particles into BNCT dosimetry, and to assess its impact on dose calculations and clinical outcome estimations.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;The photon isoeffective dose formalism was extended by reformulating the mathematical model for &lt;math&gt; &lt;semantics&gt;&lt;msub&gt;&lt;mi&gt;D&lt;/mi&gt; &lt;mrow&gt;&lt;mi&gt;I&lt;/mi&gt; &lt;mi&gt;s&lt;/mi&gt; &lt;mi&gt;o&lt;/mi&gt; &lt;mi&gt;E&lt;/mi&gt;&lt;/mrow&gt; &lt;/msub&gt; &lt;annotation&gt;$D_{IsoE}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; in terms of the secondary particle fields rather than dose components in BNCT. Tissue-specific radiobiological (RB) parameters &lt;math&gt;&lt;semantics&gt;&lt;mi&gt;α&lt;/mi&gt; &lt;annotation&gt;$alpha$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; and &lt;math&gt;&lt;semantics&gt;&lt;mi&gt;β&lt;/mi&gt; &lt;annotation&gt;$beta$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; were introduced as functions of Linear Energy Transfer (LET), as predicted by the BIANCA biophysical model for normal skin and head and neck tumor tissues. Recoil proton spectra were analyzed at superficial and deep locations in tissues to evaluate their effectiveness relative to 583 keV protons from the &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt; &lt;mn&gt;14&lt;/mn&gt;&lt;/msup&gt; &lt;mi&gt;N&lt;/mi&gt;&lt;/mrow&gt; &lt;annotation&gt;$^{14}{rm N}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; (n,p) &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt; &lt;mn&gt;14&lt;/mn&gt;&lt;/msup&gt; &lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt; &lt;annotation&gt;$^{14}{rm C}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; reaction. Four approaches to &lt;math&gt; &lt;semantics&gt;&lt;msub&gt;&lt;mi&gt;D&lt;/mi&gt; &lt;mrow&gt;&lt;mi&gt;I&lt;/mi&gt; &lt;mi&gt;s&lt;/mi&gt; &lt;mi&gt;o&lt;/mi&gt; &lt;mi&gt;E&lt;/mi&gt;&lt;/mrow&gt; &lt;/msub&gt; &lt;annotation&gt;$D_{IsoE}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; , with varying levels of detail regarding energy and radiation fields representation, were evaluated across three scenarios. The analysis moved from a simplified geometry using a cylindrical phantom irradiated with epithermal neutrons, to progressively more realistic clinical scenarios, including a head and neck cancer treatment planning case and a retrospective study of a cutaneous melanoma case treated with BNCT at the RA-6 reactor in Argentina.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;Recoil protons were found to have lower &lt;math&gt; &lt;semantics&gt;&lt;msub&gt;&lt;mi&gt;RBE&lt;/mi&gt; &lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt; &lt;mo&gt;%&lt;/mo&gt;&lt;/mrow&gt; &lt;/msub&gt; &lt;annotation&gt;${rm RBE}_{1%}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/math&gt; than 583 keV protons from &lt;math&gt; &lt;semantics&gt; &lt;mrow&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt; &lt;mn&gt;14&lt;/mn&gt;&lt;/msup&gt; &lt;mi&gt;N&lt;/mi&gt;&lt;/mrow&gt; &lt;annotation&gt;$^{14}{rm N}$&lt;/annotation&gt;&lt;/semantics&gt; &lt;/","PeriodicalId":94136,"journal":{"name":"Medical physics","volume":"53 5","pages":"e70410"},"PeriodicalIF":3.2,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147871086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}