Journal of Medical Physics最新文献

Introduction: All building materials of natural origin contain some amounts of primordial radionuclides, ⁴⁰K, ²³²Th, and ²³⁸U, as well as other radionuclides in the decay series of ²³²Th and ²³⁸U.

Purpose: The use of tiles to beautify walls and floors in dwellings has become popular worldwide and in Nigeria in particular. However, not much has been done in assessing the impact of the use of floor and wall tiles on the radiation exposure of dwellers. In this study, radioisotopes of natural origin (²²⁶Ra, ²³²Th, and ⁴⁰K) in selected ceramic tiles often used in Ibadan Southwest Nigeria were estimated and the associated radiological parameters evaluated.

Methodology: Forty-five samples of different types of floor and wall tiles were obtained from local markets within the study area. Each of the 45 samples was pulverized and sealed in an airtight sample container for 4 weeks before analysis using a sodium iodide-based gamma-ray spectrometer.

Results: The average values of ²²⁶Ra, ²³²Th, and ⁴⁰K obtained were 44.28 ± 0.56, 84.71 ± 0.60, and 830.44 ± 0.63 Bqkg^-1, respectively, which shows that they are greater than the corresponding estimated worldwide average concentration. Again, the estimated average values obtained for the radiological hazard parameters for equivalent activity due to radium and representative gamma-ray level index were found to be lower than the world averages. Similarly, the absorbed dose rates due to gamma-ray emission were found to be higher than the world common values.

Conclusion: This study indicates that the use of these tiles will not be posing potential radiological risk if used in dwellings. However, construction works that requires the use of these tiles must be designed in such a way that the emission of dangerous radiation will not be a threat to the occupants.

Purpose: According to the revised Task Group number 43 recommendations, a brachytherapy source must be validated against a similar or identical source before its clinical application. The purpose of this investigation is to verify the dosimetric data of the high dose rate (HDR) BEBIG ¹⁹²Ir source (Ir2.A85-2).

Materials and methods: The HDR ¹⁹²Ir encapsulated seed was simulated and its main dosimetric data were calculated using Geant4 Application for Tomographic Emission (GATE) simulation code. Cubic cells were used for the calculation of dose rate constant and radial dose function while for anisotropy function ring cells were used. DoseActors were simulated and attached to the respective cells to obtain the required data.

Results: The dose rate constant was obtained as 1.098 ± 0.003 cGy.h - ¹.U - ¹, differing by 1.0% from the reference value reported by Granero et al. Similarly, the calculated values for radial dose and anisotropy functions presented good agreement with the results obtained by Granero et al.

Conclusion: The results of this study suggest that the GATE Monte Carlo code is a valid toolkit for benchmarking brachytherapy sources and can be used for brachytherapy simulation-based studies and verification of brachytherapy treatment planning systems.

Purpose: The high-energy proton produces the unwanted dose contribution from the secondary neutron. The main purpose of this study is to report the validation results of in-house neutron moderator based on poly allyl diglycol carbonate (CR-39) detector, Chulalongkorn University Neutron Moderator (CUMOD) through the ambient dose equivalent, H*(10) measurement.

Materials and methods: The Particle and Heavy Ion Transport code System (PHITS) Monte Carlo code was used to simulate the neutron response function. The CUMOD was calibrated with ²⁴¹AmBe source calibrator in the range of 100-1000 μSv. The variation of neutron fields was generated employing different proton treatment plans covering most of the clinical scenarios. The ambient dose equivalents, H*(10), evaluated employing CUMOD were compared to those obtained with WENDI-II dosimeter.

Results: The linear relationship between CUMOD and WENDI-II responses showed an R² value close to 1. The H*(10) per Gy delivered dose was in the range of 22-105 μSv for a 10 cm × 10 cm field.

Conclusion: The in-house CUMOD neutron moderator can expand the neutron detection dose range of CR-39 detector for ambient dose equivalent. The advantage of CUMODs is its capability to evaluate H*(10) in various positions simultaneously.

Background: Head-and-neck cancer treatment includes radiotherapy as a crucial component. However, radiotherapy, like other treatment modalities, has its own side effects, some of which can be avoided using the latest medical technology and understanding the illness. Despite being a relatively uncommon subtype of head-and-neck cancer, radiation is essential in the treatment of nasopharyngeal carcinoma (NPC). Because of the complex anatomy of the nasopharyngeal region, it is difficult to plan radiotherapy without sparing the cochlea, an important part of the auditory system, and the radiotherapy dosage to it may cause sensorineural hearing loss. In the modern era, volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) have become the gold standard in radiotherapy. With the advancement of these techniques, cochlear sparing is now possible without compromising the tumor dose.

Materials and methods: We reviewed 14 plans for patients with locally advanced NPC who had received radiation in our department. VMAT plans were created for patients who had IMRT radiotherapy and vice versa. Both approaches were evaluated in terms of cochlea sparing while maintaining the coverage of the planned target volume (PTV).

Results: Our study compared the results of two different radiation techniques for locally advanced NPC, IMRT, and VMAT in 14 cases, and we found that VMAT was associated with a lower maximum dose to the cochlea, a lower mean dose to the cochlea, a higher PTV D98% (Gy), a lower PTV D2% (Gy), a higher PTV V95% (%), a lower heterogeneity index, and a higher conformity index. The P value for each comparison was <0.05, which indicates that the difference is statistically significant. These results suggest that VMAT is a better radiation technique than IMRT for locally advanced NPC. VMAT is associated with a lower dose to the cochlea and other organs at risk, which can improve the quality of life and survival of patients.

Conclusion: These results suggest that VMAT is a better radiation technique than IMRT for locally advanced NPC. VMAT is associated with a lower dose to the cochlea and other organs at risk, which can improve the quality of life and survival of patients.

Purpose: The focus of this work was given on the relative stopping power (RSP) using the water equivalent thickness (WET) validation on tissue substitutes and real pig organs, as well as a dosimetric comparison of proton treatment plans between single-energy computed tomography (SECT) and dual-energy computed tomography (DECT)-based dose calculations.

Materials and methods: The CT calibration curve of SECT and DECT data was generated using the stoichiometric calibration method. WET measurement was performed for RSP validation using a Giraffe dosimeter (IBA dosimetry) in various substitute tissues (Gammex) and real pig tissues. The thorax (008A, CIRS) and head (731-HN, CIRS) phantoms were used to generate proton plans. The dosimetric evaluations of SECT and DECT-based plans were performed using the gamma analysis with 1%/1 mm and the dose-volume histograms (DVHs) comparison.

Results: For RSP validation of substitute tissues, the largest percent WET difference between measurement and calculation was observed up to 17.9% (4 mm) in lung tissue, using SECT based. In real pig tissues, the average WET difference was 2.3% ± 2.1% and 2.5% ± 2.3% for SECT and DECT, respectively. The average gamma passed of about 92.1% for the lung and 96.8% for the head regions was reported. For the lung region, the DVH of the target dose was observed with a higher predicted dose in SECT than in DECT, while results in the head region were in good agreement for both SECT and DECT.

Conclusion: The performed dosimetric comparison indicates the dose differences between SECT and DECT. The impact of the CT calibration curve is more pronounced for the thorax region.

Introduction: The purpose of this study was to compare the dosimetric parameters of volumetric modulated arc therapy (VMAT) treatment plans using coplanar and noncoplanar beams in patients with bilateral breast cancer/s (BBCs) in terms of organ at risk sparing and target volume coverage. The hypothesis was to test whether VMAT with noncoplanar beams can result in lesser dose delivery to critical organs such as heart and lung, which will result in lesser overall toxicity.

Materials and methods: Data of nine BBC cases treated at our hospital were retrieved. Computed tomography simulation data of these cases was used to generate noncoplanar VMAT plans and the parameters were compared with standard VMAT coplanar plans. Contouring was done using radiation therapy oncology group guidelines. Forty-five Gray in 25 fractions was planned followed by 10 Gy in five fractions boost in breast conservation cases.

Results: No significant difference in planning target volume (PTV) coverage was found for the right breast/chestwall (P = 0.940), left breast/chestwall (P = 0.872), and in the total PTV (P = 0.929). Noncoplanar beams resulted in better cardiac sparing in terms of D_mean heart. The difference in mean dose was >1 Gy (8.80 ± 0.28 - 7.28 ± 0.33, P < 0.001). The D_mean, V₂₀ and V₃₀ values for total lung slightly favor noncoplanar beams, although there was no statistically significant difference. The average monitor units (MUs) were similar for coplanar plans (1515 MU) and noncoplanar plans (1455 MU), but the overall treatment time was higher in noncoplanar plans due to more complex setup and beam arrangement. For noncoplanar VMAT plans, the mean conformity index was slightly better although the homogeneity indices were similar.

Conclusion: VMAT plans with noncoplanar beam arrangements had significant dosimetric advantages in terms of sparing of critical organs, that is D_mean of heart doses with almost equivalent lung doses and equally good target coverage. Larger studies with clinical implications need to be considered to validate this data.

Purpose: Optimizers are widely utilized across various domains to enhance desired outcomes by either maximizing or minimizing objective functions. In the context of deep learning, they help to minimize the loss function and improve model's performance. This study aims to evaluate the accuracy of different optimizers employed for autosegmentation of non-small cell lung cancer (NSCLC) target volumes on thoracic computed tomography images utilized in oncology.

Materials and methods: The study utilized 112 patients, comprising 92 patients from "The Cancer Imaging Archive" (TCIA) and 20 of our local clinical patients, to evaluate the efficacy of various optimizers. The gross tumor volume was selected as the foreground mask for training and testing the models. Of the 92 TCIA patients, 57 were used for training and validation, and the remaining 35 for testing using nnU-Net. The performance of the final model was further evaluated on the 20 local clinical patient datasets. Six different optimizers, namely AdaDelta, AdaGrad, Adam, NAdam, RMSprop, and stochastic gradient descent (SGD), were investigated. To assess the agreement between the predicted volume and the ground truth, several metrics including Dice similarity coefficient (DSC), Jaccard index, sensitivity, precision, Hausdorff distance (HD), 95^th percentile Hausdorff distance (HD95), and average symmetric surface distance (ASSD) were utilized.

Results: The DSC values for AdaDelta, AdaGrad, Adam, NAdam, RMSprop, and SGD were 0.75, 0.84, 0.85, 0.84, 0.83, and 0.81, respectively, for the TCIA test data. However, when the model trained on TCIA datasets was applied to the clinical datasets, the DSC, HD, HD95, and ASSD metrics showed a statistically significant decrease in performance compared to the TCIA test datasets, indicating the presence of image and/or mask heterogeneity between the data sources.

Conclusion: The choice of optimizer in deep learning is a critical factor that can significantly impact the performance of autosegmentation models. However, it is worth noting that the behavior of optimizers may vary when applied to new clinical datasets, which can lead to changes in models' performance. Therefore, selecting the appropriate optimizer for a specific task is essential to ensure optimal performance and generalizability of the model to different datasets.

Aims: We investigated imaging dose and noise under clinical scan conditions at multiple institutions using a simple and unified method, and demonstrated the need for diagnostic reference levels in image-guided radiotherapy (IGRT).

Materials and methods: Nine cone-beam and helical computed tomography (CT) scanners (Varian, Elekta, Accuray Inc., and BrainLAB) from seven institutions were investigated in this study. The weighted cone-beam dose index (CBDI_w) was calculated for head and pelvic protocols using a 100 mm pencil chamber under the conditions used in actual clinical practice at each institution. Cone-beam CT image noise was evaluated using polymethylmethacrylate head and body phantoms with diameters of 16 and 32 cm, respectively.

Results: For head and pelvic protocols, CBDI_w values ranged from 0.94-6.59 and 1.47-20.9 mGy, respectively. Similarly, standard deviation (SD) values ranged from 9.3-34.0 and 26.9-97.4 HU, respectively. The SD values tended to increase with decreasing imaging dose (r = -0.33 and -0.61 for the head and pelvic protocols, respectively).

Conclusions: Among the nine machines, the imaging dose for high imaging dose institutions was approximately 20 mGy to the pelvic phantom, and there was a 14-fold difference in dose compared with the other institutions. These results suggest the need to establish DRLs for IGRT to guide clinical decision-making.