Journal of Medical Physics最新文献

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.

Purpose: Online adaptive radiation therapy (OART) poses unique challenges for quality assurance (QA), requiring innovative methodologies beyond traditional techniques. This study introduced an end-to-end (E2E) QA test for the Ethos OART system.

Materials and methods: Initial treatment plans were developed using deformed computed tomography (CT) images of standard phantoms. During treatment sessions, adaptive plans were created and delivered using undistorted physical QA phantoms equipped with measuring detectors. Our approach was demonstrated using standard QA phantoms - OCTAVIUS-four-dimensional (PTW, Freiburg, Germany), ArcCHECK (Sun Nuclear Corp., FL, USA), and the RUBY (PTW, Freiburg, Germany) - to evaluate the accuracy of contouring, synthetic CT (sCT), and dosimetry of adaptive plans in the Ethos OART system.

Results: Our findings demonstrated the superior performance of the Ethos OART system, with a gamma pass rate exceeding 96% (2% local/2 mm) and point dose deviations below 0.5%. The Dice coefficients for body contours between the sCT and reference CT were above 0.9, and the sCT accuracy was confirmed by mean absolute errors of <27 Hounsfield unit.

Conclusion: This approach establishes a straightforward E2E test to assess the workflow accuracies essential for preclinical validation/monthly QA of OART systems.

Purpose: The purpose of this study was to validate experimentally measured beam data, and treatment planning system (TPS) calculated volumetric modulated arc therapy (VMAT) three-dimensional (3D) dose distribution using PRIMO Monte Carlo (MC) simulation and one-dimensional (1D) gamma index analysis.

Materials and methods: The PRIMO code simulates the percentage depth dose (PDD) and beam profiles across varying field sizes in water phantoms, which were then compared with the ion chamber-measured beam characteristics using 1D gamma analysis. For the VMAT 3D dose distribution, the computed tomography scan of the anthropomorphic pelvis phantom was used for dose calculation and simulation in Eclipse TPS and PRIMO, respectively. Then, the doses of the target and organ at risk were compared with 1D gamma index analysis.

Results: The results show that the PDD passed the 1D gamma index above 95% of all evaluated points at 2%/2 mm criteria. There was no significant difference between the mean values of measured and MC-simulated PDD at all field sizes. The results were statistically significant as P < 0.05. For beam profile at a 10 cm depth along in-line (in-plane) and cross-line (cross-plane) directions, above 95% of all the evaluated points passed the 1D gamma index at 3%/3 mm. The matching of dose volume histogram (DVH) of TPS calculated and PRIMO simulated DVH passed 2%/2 mm and 3%/3 mm gamma index passing criteria.

Conclusions: Based on this study's findings, PRIMO MC simulation can validate experimentally measured medical linear accelerator beam data and TPS 3D dose distribution with acceptable agreement using 1D gamma analysis.

Introduction: Surface Guided Radiation Therapy (SGRT) enhances radiation therapy by providing real-time support without additional X-ray exposure. It ensures precise patient positioning, continuous monitoring, and motion management. However, closed-bore LINACs face optical line-of-sight challenges with ceiling-mounted SGRT systems.

Objective: This study commissions the AlignRT InBore™ SGRT system on the Ethos™ LINAC at a Mumbai tertiary care center, evaluating accuracy, precision, reproducibility, and temporal stability.

Methods: System Commissioning: 1) Acceptance tests per Vision RT's Form 412: Camera calibration, setup validation, thermal stability, relative shift accuracy. Phantom measurements for performance assessment. 3) Deliberate rotational motion errors to test detection capability.

Results: Comparison with Existing Systems: 1) Consistent with SGRT performance on Halcyon™ LINAC (Nguyen et al.). 2) Reliable mechanical and imaging test results. Patient-Specific QA: 1) 51 adaptive treatment sessions. 2) High gamma pass rates confirmed clinical efficacy. 3) Essential for Ethos™ LINAC, which lacks 6D couch correction.

Conclusion: This study demonstrates successful SGRT integration with Ethos™, improving treatment accuracy, patient comfort, and efficiency in closed-bore LINACs, advancing radiation oncology in India.

Aim: Focused ultrasound (FUS) therapies are often performed within magnetic resonance imaging (MRI) systems providing thermometry-based temperature monitoring. Herein, MRI thermometry was assessed for FUS sonications executed using a preclinical system on agar-based phantoms at 1.5T and 3T MRI scanners, using the proton resonance frequency shift technique.

Materials and methods: Sonications were executed at 1.5T and 3T to assess the system and observe variations in magnetic resonance (MR) thermometry temperature measurements. MR thermometry was assessed at 3T, for identical sonications on three agar-based phantoms doped with varied silica and evaporated milk concentrations, and for sonications executed at varied acoustic power of 1.5-45 W. Moreover, echo time (TE) values of 5-20 ms were used to assess the effect on the signal-to-noise ratio (SNR) and temperature change sensitivity.

Results: Clearer thermal maps with a 2.5-fold higher temporal resolution were produced for sonications at 3T compared to 1.5T, despite employment of similar thermometry sequences. At 3T, temperature changes between 41°C and 50°C were recorded for the three phantoms produced with varied silica and evaporated milk, with the addition of 2% w/v silica resulting in a 20% increase in temperature change. The lowest acoustic power that produced reliable beam detection within a voxel was 1.5 W. A TE of 10 ms resulted in the highest temperature sensitivity with adequate SNR.

Conclusions: MR thermometry performed at 3T achieved short temporal resolution with temperature dependencies exhibited with the sonication and imaging parameters. Present data could be used in preclinical MRI-guided FUS feasibility studies to enhance MR thermometry.

Purpose/aim: The increasing population age highlights the critical need for early brain disease diagnosis, especially in disorders such as dementia. Consequently, a notable focus has been on developing dedicated brain positron emission tomography (PET) scanners, which offer higher resolution and sensitivity than whole-body PET scanners. This study aims to design and performance evaluation of an LYSO-based dedicated brain PET scanner.

Materials and methods: We developed a dedicated brain PET using Monte Carlo simulation based on cylindrical geometry. Each detector block consisted of a 23 × 23 array of 2 mm × 2 mm × 15 mm LYSO crystals coupled with SiPM. The performance of this scanner was evaluated based on the NEMA NU-2-2018 standard, focusing on analyzing various energy windows and coincidence time windows (CTWs).

Results: The results demonstrated that the noise equivalent count rate (NECR) peaked at each CTW in the 408-680 keV energy window. In addition, increasing the CTWs from 3 ns to 10 ns resulted in a decrease of 9% in sensitivity and an increase of 63% in NECR. Furthermore, the study findings highlight that using a time-of-flight (TOF) resolution of 250 ps can substantially improve image contrast relative to non-TOF reconstruction.

Conclusions: We conclude that employing a broader energy window and a narrower CTW can significantly enhance the scanner's performance regarding sensitivity and NECR. Furthermore, incorporating LYSO pixelated crystals with TOF information will facilitate the generation of high-resolution and high-contrast images.