Journal of Medical Physics最新文献

Objective: This study aims to methodically explore and evaluate the effectiveness of volumetric-modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) with both flattened and unflattened 6MV beams for treating pharyngeal carcinomas.

Materials and methods: Twenty patients who had previously undergone treatment for advanced pharyngeal cancer were randomly chosen. They were replanned using a fixed nine-field dynamic IMRT and VMAT with RapidArc using both 6MV flattened and unflattened beams. A total of 80 similar treatment plans were generated for the TrueBeam SVC setup. These plans were assessed for target coverage, maximum and mean doses to the organs at risk, monitor unit (MU), beam-on time, dose to healthy tissue, and other indicators of dose quality.

Results: Target coverage was nearly identical across all the techniques. VMAT (6FF and 6FFF) achieved equivalent or superior target coverage while plans give better sparing of mean doses of parotid glands, esophagus, larynx, and maximum dose of the spinal cord while maintaining equivalent maximum dose of the brainstem. The MUs required for VMAT plans were about 4-5 times less than that of IMRT plans, additionally, the 6MV plan shows 20%-30% lesser MU than 6FFF plans in both techniques.

Conclusions: VMAT-6FFF shows fewer hot spots in the planning target volume (PTV) high-risk volume and equivalent or higher hot spots in the PTV intermediate-risk and PTV low-risk volumes. In terms of treatment time, VMAT 6FF has fewer MUs than VMAT 6 FFF. Hence, it shows that VMAT 6FF has less treatment time.

Aim: This study aimed to optimize the quantitative aspects of (¹⁸F) fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) imaging by investigating the impact of various reconstruction parameters on the recovery coefficients (RCs) using the NEMA image quality phantom. Specifically, the study aims to assess how different matrix sizes, iterations, subsets, and Gaussian postfilters affect the accuracy of standardized uptake value (SUV) quantification in (¹⁸F) FDG PET/CT imaging.

Materials and methods: The study utilized the "Vue Point FX + Sharp IR" algorithm for PET image reconstruction, incorporating 3D-ordered subset expectation maximization (3D-OSEM), time-of-flight, and point spread function technologies. Various reconstruction parameters were explored, including two distinct matrix sizes, multiple iterations, subsets, and a wide range of Gaussian postfilters. The investigation focused on the impact of these parameters on RCs using the NEMA image quality phantom.

Results: The results of the study indicated that for accurate SUV quantification in spheres ≥17 mm, the 256 × 256 matrix size and mean SUV should be employed. Conversely, for spheres ≤13 mm, maximum SUV was found to be more suitable. The choice of postfiltering value was shown to have a significant impact on SUV quantification accuracy, particularly for small-sized spheres. In addition, a larger matrix size was found to partially mitigate the effects of Gibbs artifact and slightly enhance SUV quantification for the spheres of various sizes.

Conclusion: This study highlights the critical importance of optimizing PET reconstruction parameters in accordance with the guidelines set by European Association of Nuclear Medicine/EARL. By optimizing these parameters, the accuracy and reliability of SUV quantification in (¹⁸F) FDG PET imaging can be significantly enhanced, especially for small-sized spheres. This underscores the necessity of carefully considering reconstruction parameters to ensure precise and reliable quantitative measurements in PET/CT imaging.

Purpose: This study proposes a novel approach combining mathematical modeling and machine learning (ML) to classify four Alzheimer's disease (AD) stages from magnetic resonance imaging (MRI) scans.

Methodology: We first mapped each MRI pixel value matrix to a 2 × 2 matrix, using the techniques of forming a moment of inertia (MI) tensor, commonly used in physics to measure the mass distribution. Using the properties of the obtained inertia tensor and their eigenvalues, along with ML techniques, we classify the different stages of AD.

Results: In this study, we have compared the performance of an intuitive mathematical model integrated with a machine learning approach across various ML models. Among them, the Gaussian Naïve Bayes classifier achieves the highest accuracy of 95.45%.

Conclusions: Beyond improved accuracy, our method offers potential for computational efficiency due to dimensionality reduction and provides novel physical insights into AD through inertia tensor analysis.

Purpose: This study presents the outcomes of a series of magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) sonications performed on an anatomically accurate head phantom with an embedded tumor simulator to evaluate the effectiveness of partial and complete tumor ablation with obstruction from thin polymer skull mimics.

Materials and methods: The tumor simulator was subjected to single and grid sonications using a single-element concave transducer integrated with an MRI-compatible focused ultrasound (FUS) robotic system. All experiments were carried out in a high-field MRI scanner utilizing proton resonance frequency thermometry and T2-weighted (T2-W) turbo spin echo (TSE) imaging to evaluate the induced thermal effects. FUS transmission through 1-mm thick three-dimensional-printed polymer skull mimics was compared to unobstructed sonication through a circular aperture in the skull model.

Results: T2-W TSE imaging demonstrated sharp contrast between the tumor and hyperintense FUS lesions. Complete tumor coverage was achieved through robotic-assisted grid ablation without a skull mimic, as well as with a 1-mm resin skull mimic intervening in the beam. With the lowest attenuation among tested polymers, the resin skull resulted in approximately a 20% reduction in focal temperature change compared to unobstructed sonication, yet still facilitated sharp beam focusing, raising the tumor temperature to ablative levels.

Conclusions: The study provides preliminary evidence for the potential application of a thin biocompatible implant to temporarily replace a skull portion facilitating MRgFUS ablation of inoperable tumors using a single-element transducer. The tumor-embedded head phantom was proven effective for testing MRgFUS oncological protocols and equipment.

Purpose: The purpose of this study was to investigate the tolerance limits (TL) and action limits (AL) in gamma passing rate for craniospinal irradiation volumetric modulated arc therapy (VMAT) treatment plans.

Materials and methods: Twenty-eight patients were planned using the VMAT technique; plans were delivered on an Elekta Versa HD. The delivered fluence was recorded by PTW 2D array, and the gamma passing rate (%GP) was analyzed using PTW VeriSoft. The universal TL and AL from TG 218 were applied to analyze the %GP for each plan. As per AAPM TG 218, a statistical process control of %GP was performed to set the TL and AL.

Results: The average %GP for the brain, upper spine, and lower spine was 98.4%, 98.8%, and 98.4%, respectively. The TL and AL for the brain, upper spine, and lower spine were TL: 95.1%, 95.1% and 94.8%, and AL: 89.7%, 89.3%, and 86.7%, respectively. The analysis of variance test showed that the P value in %GP among the brain, upper spine, and lower spine was >0.1679. The %GP rate between the sites was not statistically significant.

Conclusion: AAPM TG 218 guidelines are more suitable for establishing TL and AL for craniospinal irradiation (CSI) VMAT plans. This study suggests that a single value of TL and AL for CSI plans, rather than site-specific values, could be suitable for monitoring CSI patient-specific quality assurance trends and the same can be utilized.

Aim: This study aims to compare the dosimetric efficacy of RapidArc (RA) and intensity-modulated radiation therapy (IMRT) in the treatment of head-and-neck cancer, focusing on treatment efficiency and organ at risk (OAR) dose.

Materials and methods: A cohort of 10 patients with head-and-neck cancer was recreated for RA, which was earlier treated with IMRT techniques. Dosimetric parameters evaluated or planning target volume (PTV) included monitor units (MUs), beam on time (BoT), gamma passing rate (GP), and various normal tissue dose indices such as V₉₅, V₉₀, V₅₀, V₂₅, and gradient indices (gradient index [GI], low GI [LGI], high GI). In addition, doses of OARs, including the spinal cord, brainstem, cochleae, esophagus, lips, larynx, and parotid glands, were compared.

Results: RA demonstrated significant improvements in treatment efficiency, requiring fewer MU and shorter BoT, while maintaining comparable GP to IMRT. RA achieved a lower LGI, indicating better sparing of normal tissues from intermediate doses. Most other dosimetric parameters, including those for the spinal cord, parotid glands, and PRV spinal cord, demonstrated significant differences, with the RA technique showing superior performance.

Conclusion: This study highlights the dosimetric superiority of RA over IMRT, with significantly fewer MU, reduced BoT, and comparable GPs. RA achieved slightly higher mean PTV doses with similar homogeneity and conformity while delivering lower doses to critical OARs, such as the spinal cord, PRV spinal cord, and parotid glands, making it clinically advantageous.

Nasopharyngeal carcinoma (NPC) is a rare malignancy with distinct racial and geographic distribution. Due to its proximity to critical structures, NPC presents with a diverse range of symptoms and is best treated with conformal concurrent chemoradiotherapy. We report the case of a 45-year-old male diagnosed with NPC, referred for radiation therapy after receiving three cycles of neoadjuvant chemotherapy. The patient was planned for volumetric arc radiotherapy with concurrent cisplatin, following the current standard of care. The initial phase of treatment was well tolerated; however, by the 4^th week, the patient developed persistent hiccups unresponsive to conservative management. A re-evaluation of the treatment plan revealed a maximum brainstem dose of 54.32 Gy. It was hypothesized that radiation-induced edema may have stimulated the vagus nerve, leading to hiccups. The patient was treated with chlorpromazine and injectable steroids, resulting in rapid symptom resolution within 5 days.

Purpose: Awareness of radiation-induced risk led to the development of various dose optimization techniques in iterative reconstruction (IR) algorithms and deep learning algorithms to improve low-dose image quality. PixelShine (PS) by AlgoMedica Inc., USA, is a vendor-neutral deep learning denoising tool for low-dose studies, and this study analyzed its images.

Aim: The aim of this study was to assess the diagnostic value of PS-reconstructed images obtained at various low doses (LDs).

Materials and methods: A retrospective study qualitatively and quantitatively evaluated the low-dose PS-reconstructed images by comparing them with other reconstruction methods and standard dose (SD) images. A total of 85 cases were evaluated, of which 32 cases were scanned on a scanner with filtered back projection (FBP) reconstruction with LD scans performed at 70%-50% of SD. The remaining 53 cases were performed on the scanner with IR, 35 of them had LD scan at 50% of SD and 18 cases had LD scan at 33% of SD.

Results: Qualitative image analysis - The quality of low-dose images with PS and IR was almost equivalent in terms of noise magnitude and texture at 50% dose, and PS images were slightly better at 33% dose reduction. Quantitative image analysis - Low-dose PS-reconstructed images and low-dose iterative reconstructed images had similar contrast-to-noise ratio at 50% dose reduction; however, at 33% of the SD, PS-reconstructed images outperformed. The SD FBP images were equivalent to LD PS-reconstructed images (50% dose reduction).

Conclusions: Artificial intelligence-based denoising algorithms produce similar images as IR at 50% dose reduction and outperform it at 33% of the SD.

The purpose of this study is to present the multivariate analysis of the size-specific dose estimate (SSDE) and E in pediatric computed tomography (CT) imaging. Pediatric patients scheduled for CT scans of the head, thorax, and abdomen from July 2022 to February 2024 were included in the prospective study. The water-equivalent diameter (D _w), SSDE, and E were computed for each examination using the dose report of CT console display computed tomography dose index (CTD1 _vol) and dose length product (DLP). The correlation between SSDE and E on CTD1 _vol, D _w, Area _ROI, body mass index, Size⁄(LAT+AP), age, f_size , and HU _mean in the region of interest was examined using the multivariate statistical analysis with 95% level of significance (P < 0.05). The relationship between D _w and Size⁄(LAT+AP), Size⁄(LAT+AP), and f_size versus age was investigated using linear regression analysis. The mean values of SSDE for noncontrast head CT and contrast-enhanced CT were found 71.36 mGy and 97.38 mGy, respectively. While as, the mean SSDE for contrast-enhanced thorax CT was observed to be 5.82 mGy, which is less than the mean SSDE of 6.40 mGy for noncontrast thorax CT imaging. The range of the SSDE for contrast-enhanced abdomen CT is 2.05 mGy to 22.13 mGy with a mean SSDE of around 5.71 mGy and for noncontrast abdomen imaging, mean value of SSDE was 5.58 mGy. The mean value of "E" for noncontrast thorax CT imaging was observed to be 2.7 mSv with minimum and maximum 1.17 mSv to 10.10 mSv respectively, which less than the mean effective dose is of 3.64 mSv observed for contrast enhanced thorax CT imaging. The multivariate analysis suggests that SSDE is significantly correlated with CTD1 _vol, D _w, and E is found significantly dependent on DLP for both contrast enhanced and noncontrast imaging with p < 0.05. A strong positive correlation was found between D _w and Size⁄(LAT+AP), form linear regression analysis. The SSDE is crucial for radiologists evaluating pediatric CT scans and is now an international standard expected to be widely adopted. The strong positive correlation between D _w versus Size⁄(LAT+AP), indicates that Size⁄(LAT+AP),can be used as surrogate in estimate SSDE when D _w calculation is not feasible for pediatric CT imaging.

The aim of this study was to determine the influence of geomagnetic storms (GS) on the risks of developing myocardial infarction (MI), acute coronary syndrome (ACS), and stroke. The systematic review was conducted by searching PubMed database from March 16, 2023, to March 18, 2023, independently by two researchers. Out of 644 articles, a total of 6 studies were selected based on the inclusion/exclusion criteria and included in the systematic review. This systematic review confirmed the effect of GS on the risks of MI/ACS (mean relative risk [RR] 1.3-1.5) and stroke (mean RR 1.25-1.6). At the same time, it is worthnoting the limitations of this systematic review: small number of included studies and their differences in methodology, statistical analysis, and methods for assessing geomagnetic activity. The main mechanism of the negative impact of GS on the functioning of the cardiovascular system and the risk of cardiovascular complications was associated with influence on circadian biological rhythms, heart rate variability, blood pressure, and microcirculation. The authors believe that when planning further research in this area, it is necessary to correctly choose the type of local, regional or planetary geomagnetic index, depending on the goals of the study. It is also necessary to take into account the influence of concomitant somatic pathology, drug therapy, as well as the peculiarities of the individual temporary reaction of the human body to GS.