Journal of Medical Physics最新文献

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.

Introduction: To perform energy-dispersive X-ray imaging, we constructed a photon-counting X-ray computed tomography (CT) scanner to perform enhanced K-edge CT.

Methods: X-ray photons penetrating through an object were detected using a cadmium telluride flat panel detector (FPD) with pixel dimensions of 100 × 100 mm², and 720 radiograms from the FPD were sent to the personal computer to reconstruct tomograms. Gadolinium (Gd) K-edge energy is 50.2 keV, and Gd-Kedge CT was carried out using photons with an energy range of 50-100 keV.

Results: Compared with low-energy CT of 15-50 keV, the gray density of muscle and bone substantially decreased, and the image contrast of Gd media was improved utilizing Gd-K-edge CT.

Conclusion: Using the cone beam, the effective pixel dimensions were 80 × 80 μm², and blood vessels were observed at a high contrast using Gd-Kedge CT.

Introduction: The purpose of the study was to calculate, tumor control probability (TCP) and normal tissue complication probability (NTCP) in cervical cancer patients and to clinically correlate the outcomes with a follow-up period of 24 months.

Materials and methods: One hundred and fifty patients were included in the present study who received 46 Gy/23 fractions/4½ weeks of external beam radiotherapy with concurrent cisplatin chemotherapy, followed by intracavitary brachytherapy of 3 different fractionations regimens, i.e., 9.5 Gy per fraction of two fractions (50 patients in Arm1), 7.5 Gy per fraction of three fractions (50 patients in Arm2), and 6.0 Gy per fraction of four fractions (50 patients in Arm3).

Results: The median TCP value for Arm1, Arm2, and Arm3 was 99.6%, 94%, and 98.1%, respectively, (P < 0.01). The median NTCP value for bladder in Arm1, Arm2, and Arm3 was 0.17%, 0.04%, and 0.07%, respectively, (P = 0.05). The median NTCP value for rectum in Arm1, Arm2, and Arm3 was 4.73%, 4.35%, and 3.17%, respectively, (P = 0.052). The overall survival (OS) of 90%, 86%, and 84% was found for Arm1, Arm2, and Arm3, respectively, at 24 months of follow-up.

Conclusion: TCP, NTCP, and OS rates were found higher in Arm1 as compared to the other two arms. The complications found in all arms were less, low grade, and manageable. Hence, Arm1, i.e., 9.5 Gy per fraction of two fractions can be concluded as the optimum fractionation regime in terms of radiobiological parameters as well as overall patient comfort.

Objectives: The purpose of this study was to develop a prototype for controlling the water level of a three-dimensional (3D) water phantom using ultrasound sensors and Arduino technology and evaluate its performance in setting up the 3D water phantom for radiation beam measurements.

Materials and methods: A prototype consisted of an Arduino Nano board and two types of ultrasound sensors (US015 and SR04). The accuracy of both sensors was tested at various distances and the performance was evaluated through statistical analysis. The distance measurement test was performed rigorously at intervals of 2 cm from 5 cm to 21 cm, measuring an average error and a maximum deviation for each sensor.

Results: Both sensors demonstrated the measurement accuracy within 2 mm. When using the traditional and prototype-based setup methods, the measured photon and electron beam profiles did not show any significant difference. This result suggests the equivalent setup capability when using these two different 3D water phantom setup methods.

Conclusion: The ultrasound sensor-based prototype is demonstrated as a more effective device in maintaining the 3D water phantom setup consistently compared to the traditional method, which is prone to human error, and it will aid in facilitating precise phantom setup during the commissioning and routine quality assurance (QA) of linear accelerators in radiotherapy clinics.

Aims: The objective was to validate the initial beam parameters of the Davao Doctors Hospital's 6 MV Elekta Synergy Platform linac, which performs to the specification of the commissioning data per our records using the gamma-index analysis toolkit integrated inside PRIMO software.

Materials and methods: In PRIMO, a sequence of optimization processes is performed, in which the measured and simulated percent depth dose (PDD) and lateral beam profiles at various depths are compared, using the stringent gamma-index passing rate at 1%/1 mm criteria (GPR11). Using four fields of sizes 3 cm × 3 cm, 4 cm × 4 cm, 5 cm × 5 cm, and 10 cm × 10 cm, the dose is calculated on a water phantom measuring 16.2 cm × 16.2 cm × 30.0 cm. In addition, one field of size 20 cm × 20 cm is used on a 50.0 cm × 50.0 cm × 30.0 cm water phantom with a bin size of 0.2 cm × 0.2 cm × 0.2 cm at a source-surface distance of 100.0 cm.

Results: For PDD and beam profiles comparison at the largest field size, the 6.5 MeV initial electron beam energy, 0.25 MeV full-width-half-maximum energy, 0.20 cm focal spot size, and 3° beam divergence tuned configuration yield GPR11 values of 94.0% and 97.7% (PRIMO PDD and lateral beam profile at 200 mm scan depth, respectively) with a statistical uncertainty of 2.9%. For lower field sizes, the GPR11 values are consistent at more than 90% for the PDD, whereas GPR11 values of 80.3% and 70.6% for the lateral beam profiles (at 15 mm and 200 mm scan depths) at 10 cm × 10 cm and 5 cm × 5 cm, respectively. The percentage difference between the measured and simulated PDD _20,10 ratios of not more than 2.45% is observed in all field settings.

Conclusions: These tuned beam parameters are remarkably in agreement with the suggested beam parameters listed on the PRIMO website for the 6 MV Elekta linac which was optimized with a different set of measurements.

Introduction: Cancer tissue absorbs 3-8 times more glucose than normal tissue. Therefore, we developed a gadobutrol-glucose solution for 7.0T magnetic resonance imaging to visualize whole cancerous regions at high contrast.

Methods: The contrast medium consists of gadobutrol and glucose solutions, and these solutions are mixed before the vein infusion. We used readily available solutions, and the concentrations of the gadobutrol and glucose solutions were 60% and 5.0%, respectively. To visualize the cancerous region, we used two rabbits with VX7 thigh cancer. First, vein injection was carried out using a gadobutrol-saline solution containing 0.3 ml gadobutrol, and T1-weighted imaging (T1WI) was performed. Twenty-four hours after the first experiment, we performed T1WI of the VX7-cancer region using 50.3 mL gadobutrol-glucose solution including 0.3 ml gadobutrol.

Results: Compared with T1WI using the gadobutrol-saline solution, the signal intensity of the cancerous region substantially increased using the gadobutrol-glucose solution.

Conclusion: We confirmed significant signal-intensity increases in the whole VX7-cancer region of a rabbit thigh utilizing vein infusion of gadobutrol-glucose solution since the gadobutrol molecules were absorbed throughout the cancerous region along with glucose molecules.

Aim: This article examines India's present radiotherapy (RT) machine status and requirements, geographical distribution, and infrastructure need in six regional areas, which include 31 member states and union territories (UTs). It also considers the influence of the COVID-19 pandemic on India's teletherapy sector.

Materials and methods: Data from reliable resources, including Atomic Energy Regulatory Board, Global Cancer Observatory, and Directory of Radiotherapy Centres databases, were used to analyze the current status of RT machine (RTM) density, regional disparity, and COVID-19 impact on infrastructure growth-rate.

Results: In India, the number of functioning RTM and facilities are 823 and 554, respectively, with an average of 1.5 RTM per institute, of which 69.4% have only one RTM. Over the past 22 years, there has been a paradigm shift towards medical linear accelerator (linac) installation instead of telecobalt machines. Presently, there is a teletherapy density of 0.6 RTM per million population, and there is a shortfall of 1209 RTMs. There is a considerable regional disparity in the distribution of RTMs, ranging from (0.08 RTM/million-2.94 RTM/million) across different regions. There is a significant demand for RTMs in the Northern region (480) and the state of Uttar Pradesh (279). The COVID-19 pandemic temporarily impacted India's RT growth rate, reducing it from 5% to 1.9% in 2020-2021.

Conclusions: New policies must be established to accelerate the rate of RT installation growth. To better serve local populations and save patient costs, this article proposes that RT facilities be dispersed equitably across states.

Aim: Phantoms are often utilized for the preclinical evaluation of novel high-intensity focused ultrasound (HIFU) systems, serving as valuable tools for validating efficacy. In the present study, the feasibility of a homogeneous agar-based breast-shaped phantom as a tool for the preclinical evaluation of HIFU systems dedicated to breast cancer was assessed. Specifically, the effect of the increased phantom curvature on temperature increase was examined through sonications executed on two sides having varied curvatures.

Materials and methods: Assessment was performed utilizing a 1.1 MHz focused transducer. Sonications on the two phantom sides were executed at varied acoustical power in both a laboratory setting and inside a 1.5 T magnetic resonance imaging scanner. Sonications were independently performed on two identical phantoms for repeatability purposes.

Results: Temperature changes between 7.1°C-34.3°C and 5.1°C-21.5°C were recorded within the decreased and increased curvature sides, respectively, for acoustical power of 3.75-10 W. High-power sonications created lesions which were approximately symmetrically formed around the focal point at the decreased curvature side, while they were shifted away from the focal point at the increased curvature side.

Conclusions: The present findings indicate that increased curvature of the breast phantom results in deformed focal shapes and decreased temperatures induced at the focal area, thus suggesting treatment correction requirements in the form of focus control or accurate robotic movement. The developed breast-shaped phantom can be utilized as an evaluation tool of HIFU systems dedicated to breast cancer since it can visually verify the efficacy of any system.