Journal of Medical Physics最新文献

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.

Purpose: The purpose of the study was to analyze and estimate planning risk volume (PRV) margin for heart in deep inspiration breath hold (DIBH)-based left breast radiotherapy.

Materials and methods: Fifty left-sided cancer breast cases treated with volumetric modulated arc radiotherapy were included in this retrospective study. Treatment plans were created using the Eclipse treatment planning system from Varian Medical System. The treatment was delivered on TrueBeam linear accelerator (Varian). Onboard cone-beam computed tomography (CBCT) images were generated and image registration between the planning computed tomography images and the CBCT images was performed before treatment delivery. The registration provided the shifts (errors) values in 6° of freedom, namely three translational and three rotational. From the shift values, the systematic and random errors were estimated which were used to estimate PRV margin for the heart after incorporating the rotational errors with the translational errors.

Results: The systematic error values after incorporating rotational errors with translational errors were 0.13 cm (lateral) and 0.11 cm (cranio caudal [CC] and anterioposterior each), and the random error values were 0.16 cm (lateral) and 0.13 cm (CC and anterioposterior each). Based on these values, the PRV margins for the heart in all three directions were 0.24 cm (lateral), 0.20 cm (CC), and 0.19 cm (anterioposterior).

Conclusion: As per our institutional practice, the 2 mm value for PRV margin for the heart in all the three directions would suffice for appropriate sparing of the heart during DIBH-based radiation therapy.

Purpose: Electronic compensator is a time-consuming technique for breast cancer radiation treatment planning, consequently, this presents challenges for the development of automated treatment planning for the treatment plan. Thus, this study aimed to investigate the use of automated treatment planning software for the left breast.

Subjects and methods: Thirty-eight patients with left-sided breast cancer without locoregional nodes were treated with a prescribed dose of 42.4 Gy in 16 fractions. Treatment planning was performed using electronic compensators. In addition, automated treatment planning techniques were utilized, which involved automated plan generation. This facilitated the comparison of dosimetric parameters: target volume (D_max, homogeneity index [HI], and conformity index [CI]), organs at risk, plan parameters, and quality assurance.

Results: The automated treatment planning exerted lower D_max of PTV_Eval compared to electronic compensator techniques, that is, 43.4 ± 1.1 Gy and 43.9 ± 1.1 Gy, respectively (P < 0.05). Similarly, the HI of automated treatment planning was lower than other techniques, 0.10 ± 0.04 and 0.08 ± 0.03, respectively (P < 0.05). However, there were no significant differences in the CI or organs at risk between the two techniques (P = 0.11). In plan parameters, automated treatment planning required lower monitor units compared to the electronic compensator techniques, i.e., 534.3 ± 47.4 and 724.5 ± 117.9, respectively (P < 0.05). Furthermore, the automated treatment planning significantly reduced treatment time compared to electronic compensator techniques, that is, 2.3 ± 0.5 and 41.8 ± 15.1 min, respectively (P < 0.05).

Conclusions: Automated treatment planning improved the treatment plan homogeneity, reduced hotspots, enhanced treatment planning efficiency, and reduced treatment planning time and doses comparable to those of normal organs.

Purpose: As the applications of nuclear technology increase in today's world, radiation protection becomes even more important. Radiation protection is important in medical imaging applications and radiotherapy rooms. Therefore, in this research, we have investigated features of the ionizing radiation shielding of the modified cement composite with iron, strontium, zinc, and zirconium elements in the photon energy range of 15 keV to 10 MeV.

Materials and methods: To extract such features, it is necessary to use a computational method. In this research, we have done all our calculations based on the Geant4 tool based on the Monte Carlo method. This tool is a multipurpose tool that can be used for particle transport calculations such as electrons, protons, neutrons, heavy charged particles, and photons in different environments such as human tissues.

Results: The mass attenuation coefficient of the samples was calculated using the Geant4 Monte Carlo simulation tool and compared with the results of the Phy-X program, which was in good agreement. To evaluate the radiation shielding capabilities, other quantities such as the linear attenuation coefficient, the thickness of the tenth value layer, the thermal neutron cross-section, absorption rate of thermal neutrons, and the cross-section of the fast neutron removal are determined.

Conclusions: According to the quantitative results, cement composite is more effective in absorbing and weakening gamma and neutrons. Calculations of radiation shielding quantities show that cement composites containing tungsten carbide and thallium oxide waste powder are a suitable combination and a practical material for radiation control. In addition, by returning industrial waste to the production sector, they will also be effective in reducing environmental pollution. In general, the cement composite sample containing iron, thallium, zinc, zirconium, tungsten, and carbon elements shows a high potential for radiation protection applications. This study highlights the effective radiation shielding potential of cementitious composites and demonstrates the importance of advancing safety measures in medical and industrial radiation applications.

Purpose: Radiochromic film is used for quality assurance and quality control of X-ray equipment in the diagnostic radiology. In addition, three-dimensional dose distribution of computed tomography (CT) is measured. To correct the nonuniformity and uncertainty of radiochromic films for dose measurement of CT, the films are preirradiated ultraviolet (UV)-A rays. There is a difference in the UV protection strength of radiochromic films. A concern exists about the effects of the UV-A irradiation intensity. We thus irradiated with UV-A rays from the backsides of the films to assess if backside irradiation was possible.

Materials and methods: Gafchromic XR-QA2 and RTQA2 were used in this study. The UV-A rays were simultaneously irradiated on the front and backsides of each film for 12 h. The yellow layer of each film was scanned and imaged. The average pixel values ± standard deviations (SDs) were compared. In the statistical analysis, a paired t-test was performed. To compare, the active-layer densities engendered by the UV-A rays. Calibration curve was created with 48 h of preirradiation of UV-A.

Results: The mean pixel values ± SD for Gafchromic XR-QA2 on the front and backsides were 130.776 ± 0.812 and 81.015 ± 1.128, respectively. On the other hand, the mean pixel values ± SD for Gafchromic RTQA2 on the front and backsides were 62.299 ± 1.077 and 133.761 ± 1.365, respectively. The statistical results of the paired t-test were significantly different (P < 0.01) between both films. Fitting equation of the calibration curve is shown below. y = -390.47 ± 200 + (443.45 ± 10x80).5068 ± 0.0434.

Conclusion: Based on the relationship between the sensitivity of the active layer to UV-A rays and the strength of UV protection on the surface, we concluded that backside irradiation is recommended for Gafchromic XR-QA2, and frontside irradiation is recommended for Gafchromic RTQA2.

Background and aims: Ovarian and uterine tumors are among the most serious gynecological diseases and the most common cause of mortality globally. In recent times, the role of trace elements in the onset and development of tumors has come under the review. This study aimed to assess the levels of Zn and Cu in the serum of female patients with benign and malignant uterine and ovarian tumors.

Materials and methods: One hundred and twenty-four women with benign and malignant ovarian and uterine tumors were eligible for the study. Blood samples were obtained and analyzed using flame-atomic absorption spectroscopy spectrometry in Najaf City, Iraq.

Results: Serum zinc levels exhibited lower concentration (4.73 ± 1.92) in patients with malignant uterine tumors than those with benign uterine tumors (10.80 ± 1.87, P = 0.000). In contrast, the mean concentration of copper was higher in patients with malignant uterine tumors (110.37 ± 20.05 vs. 103.75 ± 14.34, P = 0.063). The serum zinc concentrations (12.73 ± 5.34 vs. 8.90 ± 2.77, P = 0.001) were higher in patients with malignant ovarian tumors. Furthermore, we found the mean serum copper levels in patients with benign ovarian tumors decreased significantly from (101.86 ± 15.44 to 86.77 ± 21.55, P = 0.002) in female patients with malignant ovarian tumors group.

Conclusions: Serum concentrations of copper and zinc increased in some study groups and declined in others. The examination of serum trace element concentrations in patients with ovarian and uterus tumors would provide us with insight into a better understanding of the pathogenesis of the tumors and also to distinguish between them.