Journal of Medical Physics最新文献

Purpose: This study aims to quantify the secondary radiation dose caused by photoneutrons during prostate cancer treatment using an 18 MV medical linear accelerator (LINAC) through Monte Carlo simulations and experimental validation.

Methods: Monte Carlo simulations were performed using G4Linac_MT to model the 18 MV photon beam of an Elekta LINAC. The simulation results were validated against experimental measurements. Neutron characteristics, including penetration, cross-section interactions, Linear Energy Transfer (LET), and dose contributions, were analyzed using an adult male ICRP phantom. Prostate treatment scenarios involved 3D-CRT plans with 4-fields, 5-fields, and 7-fields. Specific absorbed fractions (SAFs) in various organs were also evaluated.

Results: Simulation and experimental measurements showed strong agreement, with a dose error of approximately 0.74%, and 97% of dose points passed a 2%/2 mm gamma index. Intermediate neutrons constituted 87.05%, while 12.95% were fast neutrons. Neutron dose contributions were 0.63%, 0.33%, and 0.77% for the 3D-CRT 4-field, 5-field, and 7-field plans, respectively. SAF values decreased as neutron energy increased, highlighting reduced neutron interaction efficiency at higher energies.

Conclusions: Monte Carlo simulation is a reliable approach for evaluating neutron dose contributions in high-energy X-ray LINACs. Optimization of treatment plans is essential to minimize neutron-induced dose contributions.

Background: The usage of a semiconductor detector with a pinhole collimator can provide high spatial resolution due to its high intrinsic resolution. However, the collimator system has low sensitivity due to the hole's small diameter. Therefore, the optimization between the spatial resolution and sensitivity is critical for determining the image quality in the gamma camera system.

Aims and objectives: A pinhole collimator was designed and simulated to achieve the desired level of resolution and sensitivity in a gamma camera by utilizing a CdTe semiconductor detector.

Materials and methods: To conduct this objective, a simulation toolkit based on the Geant4 Application for Tomographic Emission (GATE) was employed. The imaging capabilities of the proposed system were assessed by varying the magnification factor and pinhole diameter to estimate spatial resolution and sensitivity. Moreover, a hot rod phantom was designed to evaluate the system's overall imaging functionality.

Results: Results revealed that an increase in the pinhole diameter was correlated with an increase in sensitivity, while the spatial resolution was decreasing. There were distinct variations in sensitivity and spatial resolution depending on changes in the magnification factor as well. Finally, by analyzing trade-off curves, 1.38±0.081 mm was approximately the optimal pinhole diameter for our proposed system.

Conclusion: The optimum position for a pinhole collimator with a CdTe semiconductor detector was demonstrated.

Context: This article introduces a new cloud-based point-of-care system to monitor heart rate variability (HRV).

Aims: Medical investigations carried out at dispensaries or hospitals impose substantial physiological and psychological stress (white coat effect), disrupting cardiovascular homeostasis, which can be taken care by point-of-care cloud computing system to facilitate secure patient monitoring.

Settings and design: The device employs MAX30102 sensor to collect peripheral pulse signal using photoplethysmography technique. The non-invasive design ensures patient compliance while delivering critical insights into Autonomic Nervous System activity. Preliminary validations indicate the system's potential to enhance clinical outcomes by supporting timely, data-driven therapeutic adjustments based on HRV metrics.

Subjects and methods: This article explores the system's development, functionality, and reliability. System designed is validated with peripheral pulse analyzer (PPA), a research product of electronics division, Bhabha Atomic Research Centre.

Statistical analysis used: The output of developed HRV monitor (HRVM) is compared using Pearson's correlation and Mann-Whitney U-test with output of PPA. Peak positions and spectrum values are validated using Pearson's correlation, mean error, standard deviation (SD) of error, and range of error. HRV parameters such as total power, mean, peak amplitude, and power in very low frequency, low frequency, and high frequency bands are validated using Mann-Whitney U-test.

Results: Pearson's correlation for spectrum values has been found to be more than 0.97 in all the subjects. Mean error, SD of error, and range of error are found to be in acceptable range.

Conclusions: Statistical results validate the new HRVM system against PPA for use in cloud computing and point-of-care testing.

Purpose: This study investigated the effect of Hounsfield units (HU)-relative electron density (RED) calibration curves obtained with devices from three different Computed Tomography (CT) manufacturers on dose distribution in Accuray Precision planning of patients with lung cancer.

Methods: All CT data required for treatment planning system (TPS) were obtained using the Tomotherapy "cheese" phantom. HU RED calibration curves were created with images obtained from Siemens Somatom, GE Optima, and Toshiba Aquilion devices. The obtained calibration curve was extrapolated. CT images of lung cancer patients were acquired on a single device and treatment plans were created. The existing plans were recalculated using three calibration curves and the effect of the HU RED calibration curve on dose distribution was analyzed.

Results: The results showed that different CTs did not produce significant dose differences in organ doses and PTV for Accuray TPS.

Conclusions: Based on clinical judgment, images from different CT devices can be used in treatment planning.

Background: Recently, the green synthesis process has been utilized to manufacture a large quantity of metal nanocrystallites due to its low cost and the availability of numerous natural resources and the find the activity of bacteria and viruses that in the body of humans.

Aims and objectives: In this study, nanocrystallites of selenium oxide were produced utilizing Hibiscus sabdariffa. Researchers have analyzed the antibacterial properties and nanostructure characteristics of selenium oxide nanocrystallites using various techniques methods, such as imaging microscopy, scanning electron microscopy, ultraviolet‒visible spectroscopy (UV‒VIS), transmission electron microscopy, atomic force microscopy, and X-ray diffraction (XRD) spectroscopy.

Results: According to the results, the films are discovered to have a nanocrystalline structure in a cubic spinel configuration. The crystallites are semispherical in shape and are both uniform and easily distributed. The XRD data were recorded on card number 22-1314, and the 2 θ (hkl) value was 38.351 (311). The UV‒VIS spectrum of the material exhibited a plasmon resonance peak at 272 nm, confirming the presence here of selenium oxide. This study also investigated the response of four distinct strains of pathogenic bacteria to biosynthesized selenium oxide nanoparticles (NPs). The data indicate that the biosynthesized selenium oxide NPs were highly effective against Klebsiella spp. and had the lowest effectiveness against Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli.

Conclusions: The utilization of selenium oxide nanocrystals as antibacterial agents has yielded diverse outcomes, demonstrating their remarkable efficacy in combatting Klebsiella spp.

Purpose: Medical physics professional development is limited in parts of the globe and can be aided by virtual mentoring. A global online perception survey was conducted to elucidate the characteristics of the preferred virtual mentoring program.

Methods: Informed by a literature review and pilot testing by focus groups, the survey was electronically disseminated to multiple medical physics organizations, list servers, and professional contacts. It addressed issues including factors and barriers influencing successful mentoring; mentors'/mentees' matching preferences; frequency and length of meetings; importance of defining expectations; formal agreement; and assessment of the mentoring process. Descriptive statistics were used to characterize responses including comparisons by country income level.

Results: The 396 responders (68% male and 32% female) were from 76 countries with 66% from high-income countries (HICs) and 34% from low- and middle-income countries (L&MICs). Data were provided on experience level as mentors (43% "little [occasional]", 38% "lot [regular or ongoing]") and mentees (53% "little [occasional]", and 23% "lot [regular or ongoing]"), and interest in participating in mentorship program (83% as mentor, mentee, or both). L&MIC responders were generally younger with less work experience (55% <10 years versus 28% for HIC responders). Differences between L&MIC and HIC responses occurred when considering the perceived limitations and barriers to virtual mentoring. Preferences were given to mentoring logistics (formal agreement, frequency, length, and format of meetings).

Conclusions: Factors to consider in developing a virtual mentorship program are informed by the survey results and are applicable to both HIC and L&MIC contexts, to medical physicists, and to other related professions.

Background: The response to radiation varies widely among people. Despite recent advances to conform the dose distribution to the tumor volume, it is still impossible to perform radiotherapy based on the biological characteristics of each individual. In this case, identifying a biomarker can be a step toward personalizing treatment. This research was carried out to evaluate the predictive value of dose-volume parameters and vascular endothelial growth factor (VEGF) expression on rectal proctitis toxicity in prostate cancer patients.

Materials and methods: Eighteen patients with prostate cancer who underwent helical tomotherapy were included in the study. VEGF serum level before and after treatment was obtained. Furthermore, dosimetric parameters, including rectal volume, maximum dose, V50, V60, V65, V70, and V75 were extracted. Spearman's correlation coefficient of VEGF-related and dosimetric parameters with the grade ≥1 rectal proctitis was calculated.

Results: In the rectal toxicity group, the mean value of VEGF increased significantly after treatment compared to before (P = 0.008). Despite lower values of pre- and post-treatment VEGF in the toxicity group, this difference was not statistically significant (P > 0.05). Among the dosimetric parameters, only V65 had a significantly higher value in the toxicity group (P = 0.033). The highest correlation coefficients were obtained for pretreatment VEGF values and V65 (-0.446 and 0.450).

Conclusion: The results of the study confirm the correlation of VEGF expression with the pathobiology process of rectal radiation proctitis. However, the pathobiology process of radiation proctitis is complicated. More research is needed to prove the involvement of VEGF expression in the early detection of proctitis.

Background: The induced activity is produced in the target, monitor chamber, flattening filter (FF), collimating jaws, etc., when a high-energy photon beam is utilized for radiation therapy. This may result in add-on exposure to radiation professionals.

Objective: This study aims to measure the radiation level (RL) at the treatment plane due to induced activity in the linear accelerator head.

Materials and methods: In this study, RLs were measured close to the isocenter (I), LINAC head (H), and 0.5 m lateral to the isocenter (L) inside the radiation bunker. The RLs were measured for field sizes (FS) 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm, and 40 cm × 40 cm, using 50, 100, 200, 300, 400, 500, and 1000 monitor units (MUs) at above said locations inside the bunker using 10 mega-voltage (MV), 10 MV FF free, and 15 MV radiation beam.

Results: RL increases with an increase in FS and MUs at all mentioned locations inside the bunker, except for 40 cm × 40 cm FS. The present study shows that RL increases with an increase in radiation beam energy, and there was significant RL inside the bunker at the mentioned location, even after the 1 min of high-energy radiation exposure.

Conclusion: Therefore, treatment with a high-energy beam should be scheduled in the later evening of the working day and the jaw should be closed to a minimum before entering the bunker and a sufficient time gap should be followed to minimize the additional exposure due to induced activation in high-energy treatment.

Objective: The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD)scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation.

Materials and methods: GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC^® bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques.

Results: Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as "holes" in vertebrae.

Conclusion: Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact.

Purpose: Solutions of iodine-based compounds, due to their high X-ray attenuation coefficient, are widely used as contrast agents in computed tomography (CT) imaging. This paper investigates the attenuation properties of iodine and gold to develop nanoparticle-based contrast agents, for example, composite nanoparticles (NPs) with layers of iodine and gold or a mixture of NPs of gold and iodine.

Materials and methods: A theoretical formula is derived that gives the Hounsfield Unit (HU) for different weight-by-weight (w/w) concentrations of a mixture of blood + iodine + gold. The range of compositions for which iodine + gold mixture can give a suitable HU ≥250 upon being mixed with blood, is formulated. These estimates are derived from experiments on the variation of HU values in different compositions of aqueous solutions of iodine and available data for gold.

Results: It is seen that for an aqueous solution of iodine, the suitable HU of 250 (hence giving sufficient gray level to the CT image) can be obtained with w/w concentrations of iodine being 0.0044, 0.008, and 0.0097 for observations at 80, 100, and 120 kVp, respectively. The corresponding w/w concentrations of gold NPs would be 0.0103, 0.0131, and 0.0158. With these basic results, compositions of suitable mixtures of iodine and gold are also specified.

Conclusion: Aqueous suspensions of gold NPs are suitable as contrast materials for CT imaging and can also be used as a component of a composite contrast material consisting of an iodine and gold mixture.