Journal of Medical Physics最新文献

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.

The objectives of this study were to assess the feasibility of utilizing computational calculations and the simulation of the National Cancer Institute computed tomography (NCICT) dosimetry system to obtain size-specific dose estimate (SSDE) and effective dose values resulting from the most common CT examinations in Thai pediatric patients and to evaluate age- and size-specific k conversion factor. For the calculation methods, SSDEs were calculated using the American Association of Physicists in Medicine Report No. 220 and 293 methodologies. The results revealed that SSDEs derived from CT scans of the body, obtained through the two different methods, varied by within 10%. The size of the patient and the scanning distance had an impact on the variability of E values derived from NCICT. Age- and size-specific k conversion factors may be used as a first line to estimate risk for the pediatric patients.

Purpose: Organ motion can significantly affect the accurate delivery of radiation doses to the tumor, particularly for sites such as the breast, lung, abdomen, and pelvis. Managing this motion during treatment is crucial. One strategy employed to manage motion induced from respiration is breath-hold (BH), which enhances the geometric precision of dose delivery. Our institute is transitioning to using the ExacTrac Dynamic system to facilitate patient BH using surface-guided cameras. Only 20% of our linacs are equipped with surface guidance capabilities, and due to a high patient stereotactic throughput, the ability to perform in-bunker coaching for BH patients within the bunker is limited. To address this challenge, a time-of-flight camera (ToF) was developed to coach radiotherapy patients undergoing BH procedures, allowing them to gain confidence in the process outside of the bunker and before treatment.

Methods: The camera underwent testing for absolute and relative accuracy, responsiveness under various environmental conditions, and comparison with the Elekta Active Breathing Coordinator (ABC) to establish correlation and testing on volunteers independently to assess usability.

Results: The results showed that the absolute distance measured by the camera was nonlinear due to square light modulation, which was retrospectively corrected. Relative accuracy was tested with a QUASAR motion phantom, with results agreeing to within ± 2 mm. The camera response was found to be unaffected by changes in lighting or temperature, though it overresponded under extreme temperatures. The comparison with the Elekta ABC system yielded comparable results between lung volume and changes in surface distance during BH. All volunteers successfully followed instructions and maintained BH within ± 1 mm tolerance.

Conclusions: This study demonstrates the feasibility of using a cost-effective ToF camera to coach patients before imaging/treatment, saving valuable LINAC linac and imaging system time.

Context: Using prompt gamma (PG) ray is proposed as a promising solution for in vivo monitoring in proton therapy. Despite significant and diverse approaches explored over the past two decades, challenges still persist for more effective utilization.

Aims: The feasibility of estimating proton range with PG imaging (PGI) as an online imaging guide in an anthropomorphic phantom with lung cancer was investigated through GATE/GEANT4 Monte Carlo simulation.

Setting and design: Once the GATE code was validated for use as a simulation tool, the gamma energy spectra of NURBS-based cardiac-torso (NCAT) and polymethyl methacrylate phantoms, representing heterogeneous and homogeneous phantoms respectively, were compared with the gamma emission lines known in nuclear interactions with tissue elements. A 5-mm radius spherical tumor in the lung region of an NCAT phantom, without any physiological or morphological changes, was simulated.

Subjects and methods: The proton pencil beam source was defined as a function of the tumor size to encompass the tumor volume. The longitudinal spatial correlation between the proton dose deposition and the distribution of detected PG rays by the multi-slit camera was assessed for proton range estimation. The simulations were conducted for both 10⁸ and 10⁹ protons.

Results: The deviation between the proton range and the range estimated by PGI following proton beam irradiation to the center of the lung tumor was determined by evaluating the longitudinal profiles at the 80% fall-off point, measuring 1.9 mm for 10⁹ protons and 4.5 mm for 10⁸ protons.

Conclusions: The accuracy of proton range estimation through PGI is greatly influenced by the number of incident protons and tissue characteristics. With 10⁹ protons, it is feasible to utilize PGI as a real-time monitoring technique during proton therapy for lung cancer.