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Objective:To evaluate the radiation shielding performance for a novel self-shielded ZAP-X radiotherapy system used for intra-cranial and neck treatments. The present evaluation was performed according to the relevant Chinese national standards and the clinical placement of the radiotherapy system in an unshielded treatment room.Methods:The radiation source of the ZAP-X was a 3 MV linear accelerator. A total of 33 detection sites were selected surrounding the self-shielded system at 1.3, 2.3 and 3.3 m away from the periphery of the equipment. The maximum ambient dose equivalent rate in each irradiation condition was measured accordingly. A commonly used clinical treatment plan was selected to simulate the treatment process. During the delivery of this treatment plan, the cumulative doses of these 33 sites were measured, separately. The applicable current radiation protection standard for radiotherapy in China was chosen to evaluate the radiation shielding performance of the system.Results:According to the measurement result of the ambient dose equivalent rates along the aforementioned perimeter lines, a suggestion was put forward to redefine the existing 1 m controlled area by determining the distance at which the instantaneous dose rate of 10 μSv/h will not be exceeded. This is to meet the requirements of the Chinese standard GBZ 121-2020.Conclusions:According to the existing Chinese national radiation protection standards, the self-shielded radiotherapy system in the unshielded treatment room has the clinical applicability in China. But for such a novel self-shielded system, the corresponding performance testing and radiation protection standards shall be formulated.
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Objective To analyze the room layout and shielding of three types of self-shielded accelerators, and to provide a basis for optimizing the shielding design of rooms for self-shielded accelerators. Methods We compared the radiation shielding levels (transmitted radiation dose rate outside the primary barrier and scattered radiation dose rate outside the secondary barrier) of three self-shielded accelerator rooms by Monte Carlo simulation and empirical formula calculation. Results According to Monte Carlo simulation and empirical formula calculation, for the Unity MR Linac accelerator, the scatter radiation dose rate outside the secondary barrier was significantly higher (up to five times) than the transmitted primary radiation dose rate outside the primary barrier. The scatter radiation dose rate of the cross section was significantly higher than that of the sagittal section for both Unity MR Linac and TOMO accelerators. Conclusion The differences in the shape, material, and thickness of self-shielding structures complicate the shielding calculation and design for accelerator rooms. The shielding calculation method should be improved to optimize the radiation shielding of novel accelerator rooms.
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OBJECTIVE: To explore the radiation shielding problem of Halcyon linear accelerator room. METHODS: According to the dose estimation method recommended by GBZ/T 201.2—2011 Radiation Shielding Requirements for Radiotherapy room--Part 2: Radiotherapy Room of Electron Linear Accelerators(hereinafter referred to as GBZ/T 201.2—2011) and NCRP report No.151 Structural Shielding Design and Evaluation for Megavoltage X-and Gamma-Ray Radiotherapy Facilities the required shielding thickness of 6.0 MeV Halcyon linear machine room is evaluated and compared with the existing machine room. After the equipment was put into use, we measured and verified the dose equivalent rate around each point. RESULTS: ⅰ) The transmittance of the main beam passing through the self-shielding system was 0.06%. The theoretical shielding thickness of the main beam path sites A, C and L of the accelerator(two main shielding walls and room top sites respectively) was 136.00, 130.00 and 136.00 cm, which was lower than the required shielding thickness of the main shielding area specified in GBZ/T 201.2—2011 for 6.0 MeV accelerator. ⅱ) Compared with the existing equipment rooms in the hospital, except that the thickness of the top secondary shield(80.00 cm) and the thickness of the west section of the outer wall of the labyrinth(100.00 cm) are smaller, the rest meets the shielding requirements. ⅲ) After the transformation of the computer room and the installation of Halcyon linear accelerator, the surrounding dose equivalent rate was lower than the control level required by GBZ/T 201.2—2011. CONCLUSION: The self-shielding design of Halcyon linear accelerator can effectively protect 6.0 MeV rays used for treatment, reduce the shielding thickness required for the main shielding area, reduce the shielding construction cost of the equipment room and increase the usable area of the equipment room.
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Objective: To purpose an effective solution of reducing MRI time when rapid change and gradient switching rate of gradient magnetic field are restrained by eddy current caused by self induction and mutual inductance of gradient coil in MR system. Methods: With the constraints of gradient inductance minimization and gradient magnetic field self-shielding, a mathematical model was established by combining the target field point method to solve the winding distribution of the double-plane gradient coil, so as to reduce the magnetic field energy of the gradient coil and the eddy current on the performance of the gradient coil. At the same time, in order to shorten the operation time of solving the above complex mathematical model matrix by MATLAB software, graphic processing unit (GPU) acceleration algorithm was used to realize the calculation of gradient coil. Results: By minimizing gradient inductance, eddy current effect could be effectively reduced, the magnetic field self-shielding could be realized, the gradient switching rate was good, and the overall performance of the gradient coil could be improved. Conclusion: The new target field point method for biplane gradient coil is effective and feasible, which can realize minimization of gradient inductance and designing self-shielding gradient coil of gradient magnetic field.
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Se desarrolló una metodología para la validación y el control de rutina del proceso de irradiación que se realiza en un irradiador autoblindado con fuentes de 60Co. Esta metodología fue aplicada a un irradiador modelo ISOGAMMA LLCo con el objetivo de garantizar la correcta explotación del equipo, la eficiencia de los servicios brindados y la obtención, en forma consistente, de un producto que cumpla con los atributos de calidad y las especificaciones predeterminadas
A methodology was developed for the validation and routine control of the irradiation process performed in a self-shielding gamma irradiator with 60Co sources. This methodology was applied to an irradiator model ISOGAMMA LLCo in order to ensure the proper operation of the equipment, efficiency of services provided and to consistently obtain, , a product that meets the quality attributes and default specifications