Dose reconstruction of volumetric modulated arc therapy for nasopharyngeal carcinoma based on log files and CBCT / 中华放射肿瘤学杂志

Objective:To reconstruct the dose of nasopharyngeal carcinoma and verify the results of the whole-process radiotherapy plan based on log files and cone beam CT (CBCT).Methods:A total of 15 patients with nasopharyngeal carcinoma who received volumetric modulated arc therapy (VMAT) with Halcyon accelerator in the Cancer Center of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology from February to September 2022 were retrospectively selected. Log files and CBCT for all fractionated radiotherapy were recorded. The errors of monitor unit (MU), gantry angle, and multi-leaf collimator (MLC) leaf position per control point were analyzed. The adaptive CT (aCT) were generated according to CBCT and planned CT (pCT) using a commercial software Velocity TM, and the similarities among aCT, pCT and CBCT were analyzed. The original plan was modified from the log files and imported into the treatment planning system to calculate the delivered dose on the corresponding fractionated aCT to reconstruct the fractionated dose. And all the reconstructed doses were mapped back to pCT to obtain the cumulative dose. Theγpass ratios with criteria of 2 mm/2% and 2 mm/3% and the dose differences between the planned dose and the cumulative dose in the planning target volume (PTV) and organs at risk (OAR) were compared. Results:The root mean square (RMS) and the 95th percentile of the errors of MU, gantry angle and MLC leaf position errors were within an acceptable range. The aCT generated by Velocity TM had the anatomical structure of CBCT and the resolution, contrast, noise characteristics of pCT, which could be directly used for dose calculation. Compared with the planned dose, the changes of V 70 Gy of nasopharyngeal primary tumor (PTV nx), V 68 Gy of cervical glands (PTV nd) and V 60 Gy of planning target volume (PTV1) were -0.88%±1.91%, -2.99%±2.99% and -0.63%±0.93%, respectively, and V 40 Gy of parotid gland was increased to 2.65%±2.63%. Cumulative dose showed different degrees of PTV dose decrease ( P<0.05) and parotid dose was increased ( P<0.05). The γ pass ratio (2 mm/3%) between the cumulative dose and planned dose was 97.3%±2.7% and >95.0% in 86.7% of patients. Conclusions:Based on the log files and CBCT, the whole-process dose reconstruction of nasopharyngeal carcinoma patients can be carried out. According to the results of dose reconstruction, the radiotherapy effect of the target area and OAR can be quantitatively evaluated. In the case of high dose coverage and conformity of the original plan, the reconstruction results show that the cumulative dose coverage of the target area is decreased, whereas that of the parotid gland is increased.

Use of magnetic resonance scanner with a linear accelerator during precision radiotherapy for breast cancer / 中华放射肿瘤学杂志

Magnetic resonance-guided radiotherapy (MRgRT) not only offers real time magnetic resonance (MR) imags with high-resolution and good soft tissue contrast to guide the delineation of the target volume during simulation and daily radiotherapy, but also reveals the position and shape changes of the target volumes and organs at risk (OAR) during treatment dynamically, which provides the evidence for the individual-adptive planning revision. Thus, MRgRT has the potential to dramatically impact cancer research and treatment. And this treatment mode is theoretically more suitable for the disease with obvious tissue deformation, such as breast. In this review, application of MR scanner with a linear accelerator (MR-linac) in radiotherapy workflows for breast cancer patients was summarized, and its implications and opportunities on breast cancer irradiation were highlighted.

The remote training system for quality assurance of medical electronic linear accelerators based on extended reality technology / 中华放射肿瘤学杂志

Objective:To improve the quality assurance (QA) skills of radiotherapy personnel and medical students and reduce the radiation risk of training by developing a remote training system for QA of medical electronic linear accelerators.Methods:This training system was built based on radiotherapy technology and quality control contents of medical electronic linear accelerators, and a virtual reality interactive software was developed using extended reality (XR) technology Unity 3D. A remote control module of multi-terminal platform was also developed. A multi-perspective evaluation system was adopted and a questionnaire was designed to analyze the application value of this system.Results:The training system reproduced the live environment and physical objects of medical electronic linear accelerator treatment room. It built a multi-terminal virtual simulation training system with radiotherapy technology as well as QA knowledge system. This system could provide 5G remote control of medical electronic linear accelerator for off-site quality control demonstration and guidance. By March 1, 2022, a total number of 133 people had been trained using this system, 76 valid questionnaires had been taken, of which 90.79% (69/76) of the respondents trusted the experimental results shown by the system and 88.16% (67/76) of the respondents considered the training system necessary.Conclusions:The training effect of this system is widely recognized. It fundamentally reduces the training radiation hazard and provides reference for the reform and progress of QA training mode of medical electronic linear accelerators.

Assessment of Radiation Shielding Requirements for Radiotherapy Room—Part 2: Radiotherapy Room of Electron Linear Accelerators (GBZ/T 201.2—2011): A survey of relevant personnel in medical institutions / 中国辐射卫生

Objective To investigate the awareness of the Radiation Shielding Requirements for Radiotherapy Room–Part 2: Radiotherapy Room of Electron Linear Accelerators (GBZ/T 201.2—2011) among relevant practitioners in medical institutions as well as its implementation and application situation and collect relevant problems and suggestions for an evaluation of the scientificalness, standardization, and timeliness of the standard, and to provide a scientific basis for the further revision and implementation of the standard. Methods An online questionnaire survey was conducted among relevant employees in medical institutions providing medical linear accelerator radiotherapy across 22 provinces of China, which investigated the awareness, training, application, and revision suggestions related to GBZ/T 201.2—2011. The questionnaires were collected and analyzed. Results A total of 340 relevant practitioners filled out the questionnaire. Of the participants, 66.80% were physicists; 79.11% had an awareness of the standard; 56.18% ever participated in the standard-related training; but the survey results showed that the practitioners did not have a good knowledge of the standard’s content, and the training and promotion were not enough; 83.24% thought that the standard had been widely used; 17.60% thought that the standard needed to be revised; 76.76% thought that there was a need to add calculation examples; 88.82% thought that neutron shielding needed to be considered for the 10 MV X-ray accelerator room. Conclusion The standard has been widely known in the field of radiotherapy protection. With the development of radiotherapy technology, the standard should be revised to add calculation examples and consider neutron shielding in the 10 MV X-ray accelerator room. The standard is highly technical and difficult to grasp, so the promotion and implementation goals should be appropriate for different personnel groups, the training for employees at key posts should be strengthened, and the methods recommended in the standard should be uniformly used throughout the country.

Analysis of quality control and protection level test results of medical electron linear accelerators in Shanghai, China / 中国辐射卫生

@#<b>Objective</b> To investigate the quality control and protection level of medical electron linear accelerators in Shanghai, China. <b>Methods</b> The startified random sampling method was used to cover tertiary, secondary and ungraded hospitals, and a total of 30 medical electron linear accelerators in 15 hospitals were tested for quality control and protection level according to relevant standards. <b>Results</b> Five medical electron linear accelerators failed the quality control test, with an overall inspection pass rate of 83.3% and a re-inspection pass rate of 100%. The pass rate of flatness of square X-ray irradiation field (5 cm × 5 cm)-(30 cm × 30 cm) was 83.3%, the pass rate of symmetry of square X-ray irradiation field was 96.7%, and other indices were qualified. All medical electron linear accelerator rooms passed the protection test. <b>Conclusion</b> The protection of medical electron linear accelerator rooms in Shanghai meets the requirements of national standards, and some indices do not meet the requirements of national standards in the preliminary inspection. The quality control of medical electron linear accelerators should be further strengthened to ensure the treatment effect of patients.

Design and clinical application evaluation of multi-leaf collimators / 中国辐射卫生

@#Multi-leaf collimators are devices to block rays from medical linear accelerators, which directly affect doses to targets and organs at risk by adjusting field shape and dose distribution in radiation therapy. As multi-leaf collimators are diversified in structure, there has been growing research on dosimetric comparison of various multi-leaf collimators. In this paper, we introduced the classifications of multi-leaf collimators according to their basic components, as well as the hardware structure and design features of the products of main accelerator manufacturers, including Varian’s Millennium MLC, HD120 MLC, and Halcyon, Elekta’s MLCi/i2 and Agility, and Accuray’s InCise 2 MLC and TomoTherapy. In terms of clinical application evaluation, focusing on radiotherapy plans for nasopharyngeal carcinoma, we reviewed comparative studies on the dosimetry performance of multi-leaf collimators and the effects of relevant parameters on dose distribution. We hope this review on the design and application evaluation of multi-leaf collimators can provide a reference for more innovative design and accelerator selection and parameter setting in clinical individualized treatment.

Leak and Scattering Assessment by Optically Stimulated Luminescence Dosimetry in a Helical Linear Accelerator / Valoración de Fuga y Dispersión por medio de Dosimetría de Luminiscencia Estimulada Ópticamente (OSL) en un Acelerador Lineal Helicoidal

Radiation absorbed doses to organs outside the radiation therapy treatment beam can be significant and therefore of clinical interest. Two sets of out-of-beam measurements were performed measuring the leak dose and the scattered dose, at 5 points within the accelerator components (accelerator tube and collimator) and at 21 points on the equipment and surroundings based on a positioning scheme. For this purpose, 52 Optically Stimulated Luminescence (OSL) dosimeters were used in a latest generation helical linear accelerator. Of the 200 cGy fired at a cheese-like phantom, 0.332% of the out-of-beam dose contribution was found to come from the leak and 0.784% was transformed into scattering. For these dose values, estimates of the risk of second tumors in long-term survivors indicate a reduced probability of acquiring a second secondary radiation malignancy, based on information from the 1990 BEIR Committee report.

La dosis absorbida de radiación a órganos fuera del haz de tratamiento de radioterapia puede ser significativa y, por lo tanto, de interés clínico. Se realizaron dos sets de mediciones fuera del haz para determinar la dosis de fuga y la dosis dispersa, en 5 puntos dentro de los componentes del acelerador (tubo de aceleración y colimador) y 21 puntos en el equipo y alrededores basado en un esquema de posicionamiento. Para este fin se utilizaron 52 dosímetros de luminiscencia estimulada ópticamente (OSL, Optically Stimulated Luminescence), en un acelerador lineal helicoidal de última generación. De los 200 cGy disparados a un maniquí tipo queso, se encontró que el 0.332% de la contribución de dosis fuera del haz provenía de la fuga y 0.784% se transforma en dispersión. Para estos valores de dosis, las estimaciones del riesgo de segundos tumores en los supervivientes a largo plazo indican una reducida probabilidad de contraer una segunda malignidad por radiación secundaria, según la información del informe del Comité BEIR de 1990.

Analysis of setup errors of vacuum pad combined with breast bracket fixation in linear accelerator intensity-modulated radiotherapy for breast cancer / 肿瘤研究与临床

Objective:To explore the setup errors of vacuum pad combined with breast bracket in linear accelerator intensity-modulated radiotherapy for breast cancer.Methods:The clinical data of 72 patients who received linear accelerator intensity-modulated radiotherapy after breast conserving surgery in Hai'an Hospital of Traditional Chinese Medicine from July 2017 to March 2022 were retrospectively analyzed. According to the radiotherapy fixation schemes, they were divided into vacuum pad group (24 patients), breast bracket group (27 patients) and vacuum pad combined with breast bracket group (21 patients). Cone-beam CT was used to analyze the setup errors of the fixation, and the mean value of the overall errors and the standard deviation of the system errors were calculated. The relative factors affecting the fixed setup errors were analyzed.Results:There were statistical differences among vacuum pad group, breast bracket group and vacuum pad combined with breast bracket group in the level of forward and backward (Z) direction translation error (2.11±0.41, 2.67±0.26 and 1.79±0.21) and Z direction rotation error (1.14±0.24, 1.05±0.21 and 0.91±0.22) ( F values were 45.86 and 6.21, both P < 0.05). The level of Z direction translation error in vacuum pad group was higher than that in vacuum pad combined with breast bracket group, and the difference was statistically significant ( t = 12.37, P = 0.001). The level of Z direction rotation error in breast bracket group was higher than that in vacuum pad combined with breast bracket group, and the difference was statistically significant ( t = 3.41, P = 0.001). In the breast bracket group, the planning target volume (PTV) extension boundary values in the left and right (X), up and down (Y), and Z directions were 2.02, 2.09 and 1.97; the PTV release boundary values in X, Y and Z directions of the vacuum pad group were 1.81, 2.07 and 2.25; the external boundary values of PTV in X, Y and Z directions of the vacuum pad combined with breast bracket group were 1.13, 1.51 and 1.49. The result of multifactor analysis showed that body mass index (BMI) ( OR = 4.208, 95% CI 1.438-12.312) and breast volume ( OR = 4.023, 95% CI 1.375-11.769) were the independent influencing factors of fixed setup errors (both P < 0.05). Conclusions:The application of vacuum pad combined with breast bracket in the fixed setup of linear accelerator intensity-modulated radiotherapy of breast cancer is helpful to reduce the fixed setup errors, but at the same time, the fixed setup errors is affected by the patient's BMI, breast volume and other factors.

The case and thinking for signal interference in resolver of carousel on Varian VitalBeam medical linear accelerator / 中华放射肿瘤学杂志

In this article, a case for random signal interference in resolver (or encoder) of carousel on Varian VitalBeam medical linear accelerator was illustrated. This case was considered as a rare failure of the technology platform (including TrueBeam) by Chinese, European and American technical experts in Varian. In this article, the differences of the carousel in the structure and control system between VitalBeam and traditional accelerator were comparatively analyzed to enable the peers to have a deeper understanding of resolver. The logic and methods to solve the fault were summarized, providing reference experience for analyzing the problems related to carousel. It is found that the interlocking system is imperfect, which provides a factual and technological basis for Varian to optimize the system.

Transform routine medical accelerators to achieve Flash-RT and physical performance measurements / 中华放射肿瘤学杂志

Objective:To investigate the feasibility of transforming conventional medical accelerator to achieve ultra-high dose rate required to achieve Flash radiotherapy (Flash-RT), and to understand the physical properties of the Flash-RT beam.Methods:By transforming the Varian 23CX medical accelerator, the radiation average dose rate at the isocenter was not less than 40 Gy/s. The relevant physical measurement scheme was designed to accurately measure the actual radiation dose rate of different source skin distance (SSD) conditions, the percent depth dose (PDD) curve and the off-axis dose distribution of the beam.Results:The average dose rate of 9 MeV electron beam after the transformation was measured using the HD-V2 type film, the average dose rate of 3 s was 97.9 Gy/s, and the average dose rate of 6 s was 99.27 Gy/s. When the SSD was 100 cm, 80 cm and 60 cm, the average dose rate of 9 MeV electron beam after the transformation was 99.3 Gy/s, 168 Gy/s and 297.5 Gy/s, respectively. After the transformation, the R100 of the 9 MeV beam was 2.2 cm underwater, R50 was 3.87 cm underwater, the electron range Rp was 4.58 cm, and the maximum possible energy Ep,0 on the phantom surface was 9.28 MeV. These parameters were slightly higher than those of the conventional 9 MeV beam, manifested with slight increase in the surface dose and widening high dose flat area. The overall deposit dose distribution exhibited the highest central axis and the increase in dose declines from the axis distance. Under the condition that the field size was 20 cm×20 cm and the SSD was 100 cm, the FWHM of the vertical and horizontal off-axis dose distribution curves were 16.6 cm and 16.4 cm, respectively. Conclusion:By transforming conventional medical accelerator, the average dose rate of the beam at the isocycle meets the requirement of Flash-RT, and the average dose rate under the condition of 60 cm SSD is much higher than the requirement of at least 40 Gy/s for Flash-RT.

Study of establishment of evaluation index system for stability of linac equipment / 中华放射肿瘤学杂志

Objective:To build an evaluation index system for linac stability and establish a scientific, systematic and objective evaluation standard for the stability of linac equipment.Methods:Based on the Delphi and AHP methods, a three-level index system for the stability of linac equipment was established, and the correlation coefficients and weights were calculated using Microsoft Excel 2007 and SPSS 16.0.Results:The enthusiasm of experts in two rounds was 85%(17/20) and 92%(23/25), the authority coefficients were 0.79 and 0.87, and the expert Kendall coordination coefficients were 0.957(first-level index, P<0.05), 0.637(second-level index, P<0.05) and 0.527(third-level index, P<0.05), respectively. Finally, a three-level index system covering 2 first-level indicators of mechanical treatment system and accessory system, 9 second-level indicators and 32 third-level indicators was established. The CVs of all levels of indicators were less than 0.25 and passed the consistency test. Conclusion:The evaluation index system for linac equipment stability has good scientificity, operability and versatility, which can provide theoretical and quantitative reference for linac stability evaluation and equipment purchase.

Clinical dosimetry commissioning of 1.5 T MR-linac / 中华放射肿瘤学杂志

Objective:To introduce the clinical dosimetry commissioning methods and results of the 1.5 T MR-linac.Methods:In May, 2019, an Elekta Unity 1.5 T MR-linac was installed in Cancer Hospital, Chinese Academy of Medical Sciences and dosimetry commissioning was performed with magnetic field compatible measuring instruments. Commissioning items include absolute dose calibration, data acquisition and planning system model verification.Results:Absolute dose calibration in magnetic field should be corrected by magnetic field correction factor. The standard output dose of Unity was 87 cGy. Gamma analysis (3%/2 mm) was performed on the beam collection data and the planning system calculation data. The average pass rate of dose verification of standard field test cases was 96.41%, and the TG119 test case was 98.24%. The IROC end to end test case was 97.5%(7%/4 mm).Conclusions:The planning system model and the beam collection data have good consistency. The dose verification results of the standard field and TG119 test cases meet the general tolerance limit requirements of the AAPM TG218 report, and the verification results of the IROC end-to-end test cases meet the IROC center standards.

Application and basic application process of MR accelerator in lung cancer / 中华放射肿瘤学杂志

Radiotherapy is one of the most important components of cancer treatment. Image-guided radiotherapy (IGRT) is the mainstream tool in the precision radiation oncology. Magnetic resonance (MR) accelerator can perform MRI for tumors during radiotherapy, deliver real-time tracing and monitoring of tumors and thus realize the MRI-guided adaptive radiotherapy. Here, the latest research status and clinical application of MR accelerator in lung cancer were reviewed.

Clinical implementation of MR-Linac systems in adaptive radiation therapy for head and neck cancer / 中华放射肿瘤学杂志

Adaptive radiation therapy (ART) has been proposed as a method to account for changes in head and neck cancer and normal tissues to enhance the therapeutic ratios. Online magnetic resonance-guided radiotherapy (MRgRT) using hybrid MR-Linac systems is a novel innovative application in ART for head and neck cancer. The concept of MR-Linac systems is the ability to acquire MR images for ART and also online imaging during treatment delivery. Daily ART allows to improve the targeting accuracy while avoiding organs at risk for head and neck cancer. Although an increasing number of studies related to clinical application and technical aspect of MRgRT in head and neck cancer have been published, MRgRT for ART of head and neck cancer remains in its infancy. The purpose of this article is to summarize and discuss the rationale, clinical implementation, and prospect of this promising adaptive radiotherapy modality for treating head and neck cancer.

The standard adapt-to-shape workflow for prostate cancer on MR-linac—Experience from National Cancer Institute/Cancer Hospital, Chinese Academy of Medical Sciences / 中华放射肿瘤学杂志

With aligned MR registration, the MR-Linac provides superior soft tissue resolution for prostate cancer. No fiducial markers or electromagnetic transponders insertion is needed to guarantee high-precision radiotherapy. The highly-recommended Adapt-To-Shape (ATS) workflow can resolve all the problems encountered during prostate cancer radiotherapy, including prostate volume changes and adjacent organs motion, both inter-fractionally and intra-fractionally. With all the above advantages, MR-Linac performs outstandingly than conventional linac in prostate cancer RT delivery, and probably helps us to reduce the CTV-PTV margin safely in the near future. Nevertheless, it is difficult to implement the ATS workflow in clinical practice. In this article, the standard ATS workflow for prostate cancer was summarized based on our own experience.

Preliminary application of MR-Linac in breast cancer radiotherapy in a single academic center / 中华放射肿瘤学杂志

Objective:To describe a prospective study of pre-operative tumor-bed boost performed at the 1.5 T MR-Linac in combination with adjuvant whole breast irradiation, and a first case, with an accentuation on clinical feasibility and safety.Methods:A phase II, single arm study recruiting early stage patients follows a paradigm that first boosts the tumor bed and then undergoes breast conservative surgery in 2 weeks, and last irradiates the whole breast in 6 weeks. The primary endpoint is ≥ grade 2 acute breast toxicity. A 43 years old patient affected by a breast carcinoma, not special type of the right-sided lateral quadrant, staged cT 2N 0M 0, was planned and treated. The dose, 8 Gy for one time, was calculated by Monaco on CT simulation images. Both the air electron stream effect (ESE) and the electron return effect (ERE) at the presence of 1.5 T magnetic field were evaluated. During the pre-treatment evaluation, we carried out adaptation-to-position adjustment. Results:The normal organ dosimetry is within toleration. The Dmax to the skin, the chin and the right upper arm was 8.44 Gy, 28.5 cGy and 17.8 cGy, respectively. There was no increased toxicity from ERE and ESE, and the treatment was well tolerated without > grade 1 acute toxicity. The patient received breast conservative surgery on day 7 without delayed wound healing.Conclusions:This is the first case successfully treated within a clinical trial by pre-operative tumor-bed boost under 1.5 T MR-Linac in our institution. More participants are needed to validate and optimize the paradigm.

Preliminary study of clinical application of magnetic resonance linear accelerator in liver malignancies / 中华放射肿瘤学杂志

Objective:To investigate the workflow, efficacy and safety of MR-Linac in liver malignancies.Methods:Clinical data of 15 patients with hepatocellular carcinomas (HCC) or liver metastases treated with MR-Linac between November 2019 and July 2021 were retrospectively analyzed. The workflow of MR-Linac was investigated and image identification rate was analyzed. Patients were followed up for response and toxicity assessment.Results:Fifteen patients (6 HCC, 8 liver metastases from colorectal cancer, 1 liver metastasis from breast cancer) were enrolled. A total of 21 lesions were treated, consisting of 10 patients with single lesion, 4 patients with double lesions and 1 patient with triple lesions. The median tumor size was 2.4 cm (0.8-9.8 cm). The identification rate for gross tumor volume (GTV) in MR-Linac was 13/15. Although GTV of two patients were unclearly displayed in MR-Linac images, the presence of adjacent blood vessel and bile duct assisted the precise registration. All the patients were treated with stereotactic body radiation therapy (SBRT). For HCC, the median fraction dose for GTV or planning gross tumor volume (PGTV) was 6 Gy (5-10 Gy) and the median number of fractions was 9(5-10). The median total dose was 52 Gy (50-54 Gy) and the median equivalent dose in 2 Gy fraction (EQD 2Gy) at α/ β= 10 was 72 Gy (62.5-83.3 Gy). For liver metastases, the median fraction dose for GTV or PGTV was 5 Gy (5-10 Gy) and the median number of fractions was 10(5-10). The median total dose was 50 Gy (40-50 Gy) and the median EQD 2Gy at α/ β=5 was 71.4 Gy (71.4-107.1 Gy). At 1 month after SBRT, the in-field objective response rate (ORR) was 8/13 and the disease control rate was 13/13. At 3-6 months after SBRT, the in-filed ORR was increased to 6/6. During the median follow-up of 4.0 months (0.3-11.6), 4-month local progression-free survival, progression-free survival and overall survival were 15/15, 11/15 and 15/15, respectively. Toxicities were mild and no grade 3 or higher toxicities were observed. Conclusions:MR-Linac provides a platform with high identification rates of liver lesions. Besides, the presence of adjacent blood vessel and bile duct also assists the precise registration. It is especially suitable for liver malignancies with promising local control and well tolerance.

Comparisons of dose distributions between IMPT and VMAT for pancreatic cancer / 中华放射医学与防护杂志

Objective:To compare dose distributions of hypofractionated radiotherapy for pancreatic cancer between IMPT and VMAT.Methods:Ten pancreatic cancer cases were included in this retrospective study. Photon (Edge) and proton (Proteus?PLUS) plans were designed by Eclipse and RayStation TPS, respectively. All plans were transferred to MIM system for extraction of parameters, which included Dmin, Dmean and Dmax of PTV, conformity index (CI), new conformity index (nCI), homogeneity index (HI), gradient index (GI), coverage, Dmax and dose-volume of the organs at risk (OARs). Results:There was no significant difference in CI between the two groups. The higher PTV Dmin, Dmean, Dmax, D98%, D2%, HI, coverage and the better GI, D2 cmwere found in VMAT ( t/ Z=-4.63-5.32, P<0.05). The lower 10%_PD was found in IMPT ( t=-7.47, P<0.05). Regarding the OARs, Dmax of the intestine, stomach, and duodenum and Dmean of the left kidney were similar between two groups without significant difference ( P>0.05). The D5 cm 3 of the intestine, D10 cm 3 of the stomach, D5 cm 3 and D10 cm 3 of the duodenum, D2/3 of the left kidney, Dmean and D2/3 of the right kidney were lower in IMPT than those in VMAT ( t/ Z=-8.12--2.60, P<0.05). However, the Dmax and D0.35 cm 3 of the spinal cord were higher in IMPT than those in VMAT ( t=7.30, 6.77, P<0.05). Conclusions:Both of hypofractionated radiotherapy plans of pancreatic cancer designed by VMAT and IMPT could meet clinical needs. No significant difference was found in Dmax of the adjacent gastrointestinal tracts between the two groups. While IMPT had the advantage over VMAT in the case of lower dose-volumes of the gastrointestinal tracts. Nevertheless, less protections of the OARs in front of the tumor volume could be provided by IMPT compared with VMAT.

An exploration of shielding optimization for self-shielded accelerators / 中国辐射卫生

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.

Analysis of performance test results of some medical linear accelerators in Hebei Province, China, 2019—2021 / 中国辐射卫生

@#<b>Objective</b> To investigate the current situation of quality control in medical linear accelerators in Hebei Province, China. <b>Methods</b> The main performance indices of some medical linear accelerators in Hebei Province, 2019—2021 were tested according to the current relevant effective standards GB 15213—2016 <i>Medical Electron Accelerators-Functional Performance Characteristics and Test Methods</i> and WS 674—2020 <i>Specification for Testing of Quality Control in Medical Linear Accelerator</i>. <b>Results</b> A total of 175 medical linear accelerators were tested from 2019 to 2021, and the annual pass rates were 72.4% in 2019, 75.9% in 2020, and 79.4% in 2021. The overall pass rate of initial inspection was 76.0%, and the pass rate of reinspection was 100.0%. The index with the lowest pass rate in the initial inspection was square X radiation field uniformity, followed by dose deviation and square X radiation field symmetry. <b>Conclusion</b> Medical institutions should strengthen quality control management, conduct regular testing of medical linear accelerators, and timely correct dose deviation, so as to ensure the treatment effect of patients.