Repair and maintenance multi-leaf collimator optical system of Elekta medical linear accelerator / 医疗卫生装备

The structure and working principle of the multi-leaf collimator(MLC)optical system of Elekta linear accelerator were introduced.The causes for the faults of the MLC optical system were analyzed,and the fault repair and maintenance of the MLC optical system were summarized.References were provided for medical engineers to repair and maintain the MLC optical system.[Chinese Medical Equipment Journal,2024,45(1):76-83]

Study on the design of X-ray Flash-RT equipment with high power petal accelerator / 中国医学装备

Objective:To study and design one kind of flash radiotherapy(Flash-RT)equipment with ultra-high dose rate,which can be used in the mechanism research of Flash-RT with ultra-high dose rate.Methods:Based on the technique roadmap of high-power petal accelerator,the Flash-RT equipment can realize the requirement of Flash-RT for ultra-high dose rate and multiple irradiation angles.The corresponding design and research work were carried out on the basis of the overall design of the equipment,the main components and characteristics,the dynamics design of beam,the construction of movable and preliminary experimental platform,etc.Result:The dose rate of the designed equipment can reach to 100 Gy/s at a distance of 0.8 meters from the target point,which is easy to realize the radiotherapy method with multi angles.Conclusion:The designed X-ray equipment based on the technique roadmap of high-power petal accelerator can realize the research for the mechanism of medical Flash-RT equipment with ultra-high dose rate.

A study of the performance evaluation of iCBCT imaging mode / 中华放射肿瘤学杂志

Objective:To comprehensively evaluate the performance of the iterative cone beam CT (iCBCT) imaging mode of Varian linear accelerators and to explore its specific advantages in clinical application.Methods:The kV cone beam CT (CBCT) imaging systems of Halcyon 2.0, Edge, and VitalBeam linear accelerators from Tianjin Medical University Cancer Institute & Hospital were selected, among which Halcyon 2.0 and Edge were equipped with the iCBCT imaging mode. The Penta-Guide phantom was used to evaluate the registration accuracy of iCBCT imaging modes. The accuracy of treatment couch position was measured by a ruler. The image quality of the iCBCT and conventional CBCT modes of various imaging devices were analyzed using the CatPhan604 phantom. The imaging beam-on time and reconstruction time were measured to assess image acquisition efficiency. The uniformity, spatial resolution, contrast, contrast-to-noise ratio (CNR), image acquisition time and reconstruction time between two imaging modes were statistically analyzed by t-test. Results:The maximum deviations of image registration measurement results of the iCBCT mode for Halcyon 2.0 and Edge accelerators compared to the standard values were 0.7 mm and 0.6 mm, respectively. The treatment couch position error of all devices was less than 1 mm. The iCBCT images under head scanning protocol primarily improved the uniformity and CNR. Compared to conventional CBCT images, Halcyon iCBCT increased the uniformity and CNR by 2.50% ( P<0.001) and 78.85% ( P<0.001), respectively, while Edge increased them by 2.18% ( P<0.001) and 86.42% ( P<0.001), both superior to VitalBeam CBCT images. Under pelvis scanning protocols, iCBCT images primarily improved the CNR compared to conventional CBCT images. Halcyon and Edge iCBCT increased the CNR by 113.57% ( P<0.001) and 133.87% ( P<0.001), respectively, both superior to VitalBeam CBCT images. In terms of image acquisition efficiency, the average reconstruction times for Halcyon and Edge iCBCT images increased by 7.28 s and 15.53 s, respectively, and the total image acquisition time of Halcyon accelerator was the shortest. Conclusions:While ensuring the registration accuracy, iCBCT imaging mode can significantly improve the CNR of images and improve the uniformity of images under head scanning protocol. The Halcyon imaging system can enhance image acquisition efficiency.

Feasibility of acceptance of multiple accelerators using Elekta AGL standard procedures / 中华放射肿瘤学杂志

Objective:To verify the feasibility of using Elekta accelerated go live (AGL) standard process for the acceptance of multiple accelerators.Methods:The beams of three accelerators were adjusted by PTW Beamscan three-dimensional water tank to reach the AGL standard. Dose verification was performed for three accelerators that met AGL standards. A simple field test example from Cancer Hospital Chinese Academy of Medical Sciences was used to compare the MapCheck 3 surface dose measurement results with the surface dose calculated by the same accelerator model. Images of 10 patients including head and neck, esophagus, breast, lung and rectum were randomly selected. volumetric-modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) treatment techniques were used for planning design, and the measured dose of ArcCheck was compared with the planned dose calculated by the same accelerator model. One-way ANOVA was used to statistically analyze the passing rates of two-dimensional and three-dimensional dose verification.Results:The 6 MV X-ray percentage depth dose at 10 cm underwater (PDD 10) of three accelerators was 67.45%, 67.36%, 67.47%, and the maximum deviation between the three accelerators was 0.11%. The 6 MV flattenting filter free (FFF) mode X-ray PDD 10 was 67.33%, 67.20%, 67.20%, and the maximum deviation between the three accelerators was 0.13%. All required discrete point doses on each energy 30 cm×30 cm Profile spindle of the three accelerator X-rays deviated less than ±1% from the standard data. Absolute γ analysis was performed on the results of MapCheck 3 two-dimensional dose matrix validation. Under the 10% threshold of 2 mm/3% standard, the average passing rate of the test cases in Cancer Hospital Chinese Academy of Medical Sciences was above 99%, and the difference was not statistically significant ( P>0.05). Absolute γ analysis was performed on the ArcCheck verification results. Under the 10% threshold, the pass rate of 2 mm/3% was all above 95%, the maximum average passing rate of the three accelerators with different energy and different treatment techniques was 0.28% (6 MV, VMAT), 0.19%(6 MV FFF, VMAT), 0.56% (6 MV, IMRT) and 0.05% (6 MV FFF, IMRT), and the difference was not statistically significant ( P>0.05). Conclusion:Compared with traditional accelerator acceptance process, the acceptance time of each accelerator is shortened by 4-6 weeks by using the AGL standard process, and the radiotherapy plan of patients can be interchangeably executed among different accelerators.

Analysis of the shielding effect of protective door of an 18 MV linear accelerator debugging room and its influencing factors / 中国辐射卫生

Objective To study the shielding effect of the protective door of a maze-free debugging room for an 18 MV medical linear accelerator and its influencing factors, and to provide guidance for protection of debugging personal against radioactive occupational disease hazards. Methods The investigation focused on the protective door of a newly constructed maze-free debugging room for an 18 MV medical linear accelerator. The protective door was made of the following shielding materials from inside to outside: 2.5 cm steel plate + 20 cm lead + 41 cm polyethylene containing 5% boron + 6 cm lead + 2.5 cm steel plate. The right side of the protective door was provided with a groove (commonly known as “door pocket”) lap. With different lap widths, irradiation directions, and installation positions of the accelerator base, FLUKE451P and WENDI II neutron detectors were used to measure the ambient dose equivalent rate of the points of interest outside the protective door. The shielding effect and influencing factors were analyzed. Results When the lap width at both sides of the protective door was 300 mm, the ambient dose equivalent rates outside the protective door were (1.37 ± 0.05) μSv/h on the side with “door pocket” and (4.71 ± 0.11) and (4.19 ± 0.11) μSv/h on the side without “door pocket”. When the primary beam of the accelerator was directed towards the east, the ambient dose equivalent rates at the points of interest outside the protective door were higher than those of the corresponding points of interest when the primary beam was directed towards other directions. When the accelerator base was located on the south side of the machine room, the ambient dose equivalent rates of the points of interest outside the protective door under the same irradiation conditions were lower than those when the accelerator base was located on the north side of the machine room. Conclusion The study of an 18 MV accelerator and its maze-free debugging room showed that the radiation of photons and neutrons should be taken into consideration when designing the protective door at the entrance. The protective door with shiplaps on both sides of the wall has improved shielding effect outside the door.

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.

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.

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.

Differential study of intensity modulated radiation therapy(IMRT)for cervical cancer in two different radiotherapy devices / 医疗卫生装备

Objective To investigate the differences between Elekta Synergy and Varian Halcyon accelerators in intensity modulated radiotherapy for cervical cancer.Methods Totally 60 cases of postoperative cervical cancer patients treated with radiotherapy in the radiotherapy center of some hospital from June 2021 to December 2022 were selected retrospectively,who were divided into a Halcyon group(30 cases)and a Synergy group(30 cases)according to the equipment involved.The Halcyon group with dynamic IMRT technique and the Synergy group with static IMRT technique were compared in terms of dosimetric parameters in the target area and organs at risk,gamma passing rate,setup error and treatment efficiency.SPSS 24.0 software was used for statistical analysis.Results The two groups had the dosimetric distributions meet clinical requirements.The Halcyon group behaved better than the Synergy group in target area homogeneity index,conformity index and gradient index(P＜0.001),which had lower irradiation dose in some endangered organs;the gamma passing rate was higher in the Halcyon group than that in the Synergy group(P＜0.01),while the dispersion was lower in the Halcyon group;there were no significant differences between the setup errors of the two groups in the left-right,head-foot,and up-down directions(P＞0.05);the two groups had no statistical differences in the number of monitor units(P＞0.05),while the Halcyon group had the plan execution time and total treatment time much shorter than those of the Synergy group(P＜0.001).Conclusion Halcyon accelerator gains advantages in dosimetric parameters and treatment efficiency over the traditional Synergy C-arm accelerator in intensity modulated radiotherapy for cervical cancer.[Chinese Medical Equipment Journal,2023,44(9):53-58]

Eleven-year operation analysis and optimized management of medical linear accelerator in some hospital / 医疗卫生装备

The Elekta Synergy Linear Accelerator in some hospital from 2012 to 2022 were retrospectively analyzed in terms of operation,failure time distribution and failure of each system.Some countermeasures were put forward accordingly to decrease the failure rate and strengthen the training of relevant personnel's operation and maintenance.References were provided for effective management and operation of medical 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.

Feasibility assessment of Halcyon 3.0 dual-isocenter IMRT plan in postoperative radiotherapy of radical mastectomy for left side of breast cancer / 中国医学装备

Objective:To assess the feasibility of the designed dual-isocenter IMRT plans based on Halcyon 3.0 linear accelerator in postoperative radiotherapy of radical mastectomy for left side of breast cancer.Methods:A total of sixteen patients received the postoperative radiotherapy of radical mastectomy for left side of breast cancer at Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine from December 2022 to June 2023 were retrospectively selected.The dual-isocenter plans based respectively on Halcyon 3.0 linear accelerator and Truebeam linear accelerator were designed,and the dosimetric parameters included conformity index(CI)values of target region,homogeneity index(HI)values and doses to organs at risk(OAR)of the two plans were calculated as statistic method.And then,the dosimetric performance of Halcyon 3.0 dual-isocenter plan was compared and analyzed.Utilizing two dose verification tools,ArcCHECK and Portal Dosimetry,to assess the precision of beam delivery of Halcyon 3.0 dual-isocenter plan.Results:The Halcyon dual-isocenter plan and the Truebeam single-isocenter plan had similar plan quality.There were not statistically significant differences(P>0.05)in dosimetric parameters such as CI,HI,exposure dose to 2%of the target volume(D2%)and exposure dose to 98%of the target volume(D98%).Compared to the average monitor unit(MU)of Truebeam single-isocenter plan,the MU values of Halcyon 3.0 dual-isocenter plan increased by 366 MU,while the difference was not statistically significant(P>0.05).The Halcyon 3.0 dual-isocenter plan provided comprehensive protection for OAR,which was better than that of the Truebeam single-isocenter plan.The values of the left side of lung volume(V20)that were covered by 20 Gy dose of the Halcyon 3.0 dual-isocenter plan and the Truebeam single-isocenter plan were respectively 20.41%±1.56%and 24.88%±2.95%,and the difference was statistically significant(t=6.413,P<0.05).There were not significant differences in other OAR dosimetric parameters between the two kinds of plans(P>0.05).The verification pass rates of the Halcyon 3.0 dual-isocenter plans on the ArcCHECK and Portal Dosimetry platforms were respectively 97.6%-98.9%and 98.1%-100%when the ratio of dose tolerance(DT)to distance to agreement(DTA)was set at 2%/2 mm.The verification pass rates of the Halcyon 3.0 dual-isocenter plans on the ArcCHECK and Portal Dosimetry platforms were respectively 99.1%-100%and 99.7%-100%when DT/DTA was set at 3%/3 mm.The beam delivery precision of the Halcyon 3.0 dual-isocenter plan could meet verification standards of clinical treatments.Conclusion:The Halcyon 3.0 dual-isocenter IMRT plan demonstrates a higher feasibility in the postoperative radiotherapy of radical mastectomy for left side of breast cancer.The precision of dose delivery of plan is high,and the dose of target area is sufficient,uniform and favorable conformability.It can effectively limit the OAR exposure dose at the same time.

Evaluation on the stability of positioning precision of the leaves of accelerator MLC under different gantry angles / 中国医学装备

Objective:To evaluate the stability of the positioning precisions of the leaves of accelerator multi-leaf collimator(MLC)at different gantry angles,so as to determine whether the positioning precision of leaf is affected by the gantry angle.Methods:The HD 120 MLC of American Varian Edge medical linear accelerator at our hospital was selected,and the Varian Eclipse radiotherapy planning system was used to design test cases.One test plan included 5 dynamic subfields(named PMLCE)was designed,which ray amount was 100MU,and small machine head was kept at 0°position,and the numbers of the positions of corresponding leaves of each control point were respectively-20,-15,-10,-5,0,5,10 and 12 that were 8 in total,and the dose rate was set at 500MU/min.In test,all leaves slid as uniform velocity from one extreme position to the opposite extreme position,and the movement distance of leaves between the adjacent control points was 5 cm.The PMLCE test plan was executed on the EDGE linear accelerator by using the IEC1217 coordinate system,and each test was conducted at eight different gantry angles(0°,45°,90°,135°,180°,225°,270° and 315°),and a total of 8 treatment log files of accelerator were obtained.A program was written by using Matlab2016a(MathWorks,USA)software to read the log files of accelerator,and extract out leaf position data,and calculate the deviation between the actual position and planned position of all leaves,and record a total of 960 data of positioning deviations of 120 leaves at 8 leaves positions which included in each file.The above acquisition scheme of data was performed per three days for 10 times,and then the average value was obtained.There were the data of positioning deviations of a total of 8 groups of HD 120 MLC at different gantry angles.The above 8 groups of data were analyzed as statistical method.Results:Under various angles,the range of the percentage of"leaf positioning deviations≤10 μm"was between 45.7%and 58.3%,and that of"leaf positioning deviations≤30 μm"was between 95.6%and 99.2%.When the gantry angle was at 0° and 180°,the leaf positioning accuracy was relatively higher,and the percentages of"leaf positioning deviations≤10 μm"were respectively 58.3%and 57.9%.The maximum positioning error of the HD 120 MLC did not exceed 43.3 μm.The results of the one-way ANOVA showed that there were significant differences in the average positioning precisions between 0° and each one of 45°,90°,135°,225°,270° and 315°,and between 90° and 180°,and between 135° and 180°,and between 180° and each one of 225°,270° and 315° under the gantry angles were respectively 0°,45°,90°,135°,180°,225°,270° and 315°,and under the observation values of the positioning precision of 8 leaf positions(F=4.32,F=5.67,F=3.98,F=3.85,F=6.14,F=2.87,F=4.89,F=4.56,F=4.12,F=5.01,F=6.77,P<0.05).There were no significant differences in the positioning precision among other gantry angles.Conclusion:The positioning precisions of HD 120 MLC leaf under different gantry angles can be kept at higher level,but the influences of gantry angles on the positioning precision of leaf indeed existed.Therefore,doctors and physicists should fully consider these factors under the design stage of treatment plan,so as to optimize the dose distribution and enhance the treatment outcomes.

Dosimetric evaluation of different aperture shape controller parameters based on the Halcyon 3.0 accelerator in the hippocampal avoidance-whole brain radiotherapy / 中华放射医学与防护杂志

Objective:To evaluate the dosimetric effects of different aperture shape controller (ASC) parameters based on the Halcyon 3.0 accelerator in the hippocampal avoidance-whole brain radiotherapy (HA-WBRT) plans.Methods:This study enrolled 13 patients treated with WBRT using a Halcyon 3.0 accelerator at the Department of Radiotherapy of the Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine. According to different aperture shape controller (ASC) parameters, the HA-WBRT plans were divided into six groups, namely non, very low, low, moderate, high, and very high ASC settings, marked by AO, AVL, AL, AM, AH, and AVH, respectively. This study presented a statistical evaluation of the effects of different ASC parameters on conformity index (CI), homogeneity index (HI), radiation doses to the hippocampus and other organs at risk, and the plans’ execution efficiency. Furthermore, using two dose verification tools, namely ArcCHECK and Portal Dosimetry, this study delivered a comprehensive analysis of the differences in beam delivery precision of the plans with different ASC parameters.Results:The six groups all met the requirements for clinical treatment. They had similar CI and HI values, with no statistically significant differences ( P > 0.05). The AVH group showed better protection effects on organs at risk. Compared to the control group, the AVL group showed lower Dmax of brainstems but higher Dmax of chiasma opticum ( F = 6.26, 8.04, P < 0.05). Compared to the control group, the AH group showed lower Dmax of eyeballs but higher Dmax of optic nerves ( F = 2.04, 1.37, P < 0.05). In contrast, the AVH group exhibited lower Dmax of brainstems, eyeballs, and lens than the control group ( F = 6.26, 2.04, 2.02, P < 0.05). No statistically significant differences were observed in dosimetric indices of other organs at risk ( P > 0.05). As verified using ArcCHECK and Portal Dosimetry, the γ passing rates of the six groups were over 98% at 2%/2 mm and 100% at 3%/3 mm. The overall γ passing rates verified using ArcCHECK were lower than those verified using Portal Dosimetry. The maximum difference in the monitor unit among the six groups was less than 15, and these groups did not show significant differences in terms of execution efficiency. Conclusions:The HA-WBRT plans based on the Halcyon 3.0 accelerator can meet the requirements for clinical treatment. Different ASC parameters can significantly optimize the dosimetric parameters. Among them, the AVH parameters can highly reduce the radiation dose to organs at risk. Furthermore, different ASC parameters show insignificant effects on beam delivery precision and plan execution efficiency, meeting the verification standards for clinical therapeutic doses.

Monte Carlo simulation of photoneutron for a 15 MV medical linear accelerator / 中华放射医学与防护杂志

Objective:To study the photoneutron radiation field caused by photonuclear reaction during the operation of high energy medical linac.Methods:Monte Carlo was used to simulate the photoneutron pollution of Clinic 2300CD medical electron accelerator in 15 MV X-ray mode. The photoneutron spectrum at different positions of the head and the variation in neutron ambient dose equivalent in different irradiation fields were investigated, and the dose distribution of photoneutron on the isocenter plane and the dose attenuation in the water model were analyzed.Results:When the collimator was closed, the average photoneutron energy at the lower surface of target, primary collimator, flattening filter and multi-leaf collimator was 1.08, 1.20, 0.35 and 0.30 MeV, respectively. The neutron ambient dose equivalent at the isocenter first increased and then decreased with the irradiation field expanding, reaching the maximum in about 30 cm × 30 cm irradiation field. With the increase in the depth of the measuring point in water phantom, the neutron fluent first increased and then decreased, while the neutron dose gradually decreased. In different irradiation fields, the photoneutron dose rate was almost close to the background when the depth of the water was 20 cm.Conclusions:By exploring the photoneutron spectrum and dose distribution characteristics of the high energy medical linac head, as well as the dose deposition mechanism of photoneutron in water phantom, this study provides data support for further research on the additional dose and secondary cancer effects on patients caused by photoneutron pollution from the high energy medical linac.

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.

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.

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.