ABSTRACT
Objective:To propose a markerless beam's eye view (BEV) tumor tracking algorithm, which can be applied to megavolt (MV) images with poor image quality, multi-leaf collimator (MLC) occlusion and non-rigid deformation.Methods:Window template matching, image structure transformation and demons non-rigid registration method were used to solve the registration problem in MV images. The quality assurance (QA) plan was generated in the phantom and executed after manually setting the treatment offset on the accelerator, and 682 electronic portal imaging device (EPID) images in the treatment process were collected as fixed images. Meanwhile, the digitally reconstructured radiograph (DRR) images corresponding to the field angle in the planning system were collected as floating images to verify the accuracy of the algorithm. In addition, a total of 533 images were collected from 21 cases of lung tumor treatment data for tumor tracking study, providing quantitative results of tumor location changes during treatment. Image similarity was used for third-party verification of tracking results.Results:The algorithm could cope with different degrees (10%-80%) of image missing. In the phantom verification, 86.8% of the tracking errors were less than 3 mm, and 80% were less than 2 mm. Normalized mutual information (NMI) varied from 1.182±0.026 to 1.202±0.027 ( P<0.005) before and after registration and the change of Hausdorff distance (HD) was from 57.767±6.474 to 56.664±6.733 ( P<0.005). The case results were predominantly translational (-6.0 mm to 6.2 mm), but non-rigid deformation still existed. NMI varied from 1.216±0.031 to 1.225±0.031 ( P<0.005) before and after registration and the change of HD was from 46.384±7.698 to 45.691±8.089 ( P<0.005). Conclusions:The proposed algorithm can cope with different degrees of image missing and performs well in non-rigid registration with data missing images which can be applied in different radiotherapy technologies. It provides a reference idea for processing MV images with multi-modality, partial data and poor image quality.
ABSTRACT
Objective:To analyze the differences in dosimetric quality and plan complexity of volumetric modulated arc therapy (VMAT) plans based on Halcyon 2.0 and Truebeam for different treatment sites of the patients.Methods:Halcyon 2.0 VMAT plans in head & neck, chest, abdomen, and pelvis treatment sites of 49 cases were retrospectively selected and the VMAT plans were re-designed based on Truebeam with the same optimization parameters. The differences in dosimetric metrics and plan complexity between the two types of plans were compared and analyzed. P<0.05 was considered as statistically significant. Results:In terms of PTV, Halcyon 2.0 plans showed better homogeneity index (HI), conformal index (CI) in the head & neck and chest. Besides, Halcyon 2.0 plans yielded better D 98% and CI in the abdomen and better D 2% in the pelvis. For organs at risk (OAR), the D 20% and D mean of bilateral lungs, and D meanof heart for Halcyon 2.0 plans in the chest were lower than those for Truebeam plans (all P<0.05). For the complexity metrics, the median average aperture area variability (AAV) of Halcyon 2.0 plans in the head & neck, abdomen and pelvis were 0.414, 0.425 and 0.432, which were better than 0.385, 0.368 and 0.361 of Truebeam plans in the corresponding sites, respectively. In the abdomen and pelvis, Halcyon 2.0 plans showed better median modulation complexity score (MCS) than Truebeam plans (0.320 vs. 0.268, 0.303 vs. 0.282; both P<0.05). The median small aperture score (SAS) for all plans of Halcyon 2.0 were better than that of Truebeam plans (all P<0.05), and the median plan average beam area (PA) of all plans of Halcyon 2.0 were larger than that of Truebeam plans (all P<0.05). Conclusions:Compared with conventional fractionated VMAT plans based on Halcyon 2.0 and Truebeam, Halcyon 2.0 plans have similar or even better dosimetric quality. However, Halcyon 2.0 plans have lower plan complexity, which makes it an advantage in clinical application.
ABSTRACT
To investigate the γ pass rate limit of plan verification equipment for volumetric modulated arc therapy (VMAT) plan verification and its sensitivity on the opening and closing errors of multi-leaf collimator (MLC), 50 cases of nasopharyngeal carcinoma VMAT plan with clockwise and counterclockwise full arcs were randomly selected. Eight kinds of MLC opening and closing errors were introduced in 10 cases of them, and 80 plans with errors were generated. Firstly, the plan verification was conducted in the form of field-by-field measurement and true composite measurement. The γ analysis with the criteria of 3% dose difference, distance to agreement of 2 mm, 10% dose threshold, and absolute dose global normalized conditions were performed for these fields. Then gradient analysis was used to investigate the sensitivity of field-by-field measurement and true composite measurement on MLC opening and closing errors, and the receiver operating characteristic curve (ROC) was used to investigate the optimal threshold of γ pass rate for identifying errors. Tolerance limits and action limits for γ pass rates were calculated using statistical process control (SPC) method for another 40 cases. The error identification ability using the tolerance limit calculated by SPC method and the universal tolerance limit (95%) were compared with using the optimal threshold of ROC. The results show that for the true composite measurement, the clockwise arc and the counterclockwise arc, the descent gradients of the γ passing rate with per millimeter MLC opening error are 10.61%, 7.62% and 6.66%, respectively, and the descent gradients with per millimeter MLC closing error are 9.75%, 7.36% and 6.37%, respectively. The optimal thresholds obtained by the ROC method are 99.35%, 97.95% and 98.25%, respectively, and the tolerance limits obtained by the SPC method are 98.98%, 97.74% and 98.62%, respectively. The tolerance limit calculated by SPC method is close to the optimal threshold of ROC, both of which could identify all errors of ±2 mm, while the universal tolerance limit can only partially identify them, indicating that the universal tolerance limit is not sensitive on some large errors. Therefore, considering the factors such as ease of use and accuracy, it is suggested to use the true composite measurement in clinical practice, and to formulate tolerance limits and action limits suitable for the actual process of the institution based on the SPC method. In conclusion, it is expected that the results of this study can provide some references for institutions to optimize the radiotherapy plan verification process, set appropriate pass rate limit, and promote the standardization of plan verification.
Subject(s)
Humans , Radiotherapy, Intensity-Modulated , Immune Tolerance , Nasopharyngeal Carcinoma , ROC Curve , Nasopharyngeal Neoplasms/radiotherapyABSTRACT
Dynamic multi-leaf collimator, which has the function of radiation beam shaping, is a key executive component of tumor precise radiotherapy, and plays a core role in improving the accuracy, efficiency and quality of radiotherapy. A new type of collimator leaf end structure with circular arc and plane combination was studied, and collimator penumbra performance analysis model combining analytical expression and graphic analysis was developed. The influence of leaf end structure on penumbra was analyzed quantitatively, and a set of three-dimensional structure design of dynamic multi-leaf collimator was completed. The feasibility of the structural design and analysis model was verified through experimental measurements.
Subject(s)
Humans , Radiotherapy Planning, Computer-Assisted/methods , Particle Accelerators , Neoplasms , Radiotherapy DosageABSTRACT
@#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.
ABSTRACT
Objective:To provide a new morning check method for the output dose stability of the multileaf collimator (MLC) of the CyberKnife M6 (CK-M6) system.Methods:The CT images of a verification phantom with a size of 20 cm × 20 cm × 10 cm were transmitted into the Precision Treatment Plan ning System (ver. 1.1.1.1). The high-precision alignment between the accelerator output front and the fixed position of the phantom surface was achieved using the fiducial tracking method. A 10 cm × 10 cm radiation field was formed by the MLC and a DailyCheck plan with an output of 200 MU was designed. The repeatability, sensitivity, and accuracy of the DailyCheck plan were measured, and the CK-M6 system was continuously tested for one month using the artificial fixed method and the DailyCheck plan designed in this study. Results:The average and the standard deviation of 10 repeated measurements by the DailyCheck plan were 492.28 pC and 0.09, respectively, indicating good stability. There was a linear correlation between the measured values and the output dose, with a correlation coefficient of R2 > 0.999. Moreover, there was a position deviation of 2 mm between the phantom and the accelerator output front, and the result ant effect on the measured values was equivalent to a dose deviation caused by an output of 1.24 MU. The result from the continuous measurement of both the artificial fixed method and the DailyCheck plan fell within permissible limits, showing high consistency. Conclusions:The DailyCheck plan established through the fiducial tracking of a verification phantom can achieve the convenient, quick, and accurate daily detection of the output dose stability of the MLC of CK-M6. Therefore, this method can be widely applied in the clinical quality control of the CK-M6 system.
ABSTRACT
OBJECTIVE@#To investigate the influence of positioning accuracy of the multi-leaf collimators (MLC) on the passing rate of the plan dose verification for volumetric modulation arc therapy (VMAT) of cervical cancer using an Elekta linear accelerator.@*METHODS@#The dose distributions were measured using Sun Nuclear's Mapcheck and Arccheck semiconductors matrix before and after MLC calibration in30 cervical cancer patients undergoing VMAT. Dosimetric comparisons were performed with 2D and 3D gamma passing rates of 3%, 3 mm and 2%, and 2 mm. The 3D gamma distribution was reconstructed with respect to the patient's anatomy using 3DVH software to evaluate the possible influence of MLC positioning accuracy.@*RESULTS@#Before and after MLC calibration, the gamma passing rates of Mapcheck were (88.80±1.81)% and (99.25 ± 0.53)% under 3% and 3 mm standard, respectively, with an average increase of 10.45%. The corresponding gamma passing rates of Arccheck were (87.61±1.98)% and (98.13±0.99)%, respectively, with an average increase of 10.52%. The gamma passing rates of 3DVH were (89.87±2.28)% and (98.3±1.15)%, respectively, with an average increase of 8.43%.@*CONCLUSION@#The MLC positioning accuracy is one of the main factors influencing dosimetric accuracy of VMAT for cervical cancer. The application of Autocal software facilitates MLC calibration and improves the accuracy and safety of VMAT delivery for cervical cancer.
Subject(s)
Female , Humans , Particle Accelerators , Quality Control , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Intensity-Modulated/methods , Uterine Cervical Neoplasms/radiotherapyABSTRACT
Objective:To evaluate the dosimetric effect of multi-leaf collimator (MLC) position error on dynamic intensity-modulated radiotherapy (dMLC-IMRT), aiming to provide guidance for the establishment of MLC quality control accuracy and operation tolerance.Methods:In the phantom study, the virtual water phantom established in the treatment planning system (TPS), and three dynamic sliding window test fields with gap width of 5 mm, 10 mm and 20 mm were designed. Clinical treatment plans of 7 common tumor types were extracted, including nasopharyngeal carcinoma, glioma, lung cancer, esophageal cancer, cervical cancer, prostate cancer, and breast cancer, with 6 cases in each. MLC errors were introduced into the copy from original plan to generate the simulation plans. MLC errors included systematic open/close error, systematic deviation error and random error. The dosimetric differences between the original and simulation plans were compared.Results:The phantom study showed that the symbol of dose deviation was the same as that of systematic open/close error, and the value was increased with the increase of MLC error and decreased with the increase of gap width. The results of patient study showed that the systematic open/close error had a significant effect on dosimetry, the target volume dose sensitivities of different plans were 7.258-13.743%/mm, and were negatively correlated with the average field width. The dosimetric deviation caused by the systematic shift error below 2 mm was less than 2%. The dosimetric change caused by the random error below 2 mm could be neglected in clinical treatment.Conclusions:The minimal gap width should be limited in TPS, whereas the quality control of MLC should be strengthened. In addition, for the dynamic intensity-modulated treatment technology, 2 mm random error was suggested to be the operation tolerance during treatment delivery, and 0.2 mm alignment accuracy on each side (or 0.4 mm unilateral) is recommended to be the MLC quality control accuracy to ensure the dose accuracy of radiotherapy for different tumors.
ABSTRACT
Objective:To evaluate the effect of leaf position error of Varian high-definition multi-leaf collimator (HD120) on the dosimetry of stereotactic body radiation therapy (SBRT) for lung tumors.Methods:Nine SBRT plans based on HD120 for lung tumors were selected as the reference plans. The parameters of the plans were modified by the in-house program based on the Varian Eclipse 15.6 scripting application program interface to generate the simulation plans with three types of leaf position errors including the isotropic systematic error, the anisotropic systematic error and the random error, respectively. Then, the dosimetric metric deviation between each simulation plan and the corresponding reference plan was calculated and regression analysis was performed to evaluate the dosimetric effect of three types of leaf position errors of HD120 on SBRT.Results:The planning target volume (PTV) D 99%, D 2cm and V 5Gy of double lungs were decreased quadraticly with the increase of the absolute value of the isotropic systematic error. The first-order sensitivity was -0.06%/mm to -0.26%/mm, and the second-order sensitivity was -0.55%/mm 2 to -1.17%/mm 2 ( R2=0.96-0.99, P<0.01). The maximum change of PTV D 99% was -3.13%. The linear regression analysis of the effects of the anisotropic systematic error and random error showed that the sensitivity of CI was 25.16%/mm ( R2=0.98, P<0.01) and -4.84%/mm( R2=0.99, P<0.01), and the sensitivity of other dosimetric deviations with the anisotropic systematic error was 4.80%/mm to 5.12%/mm ( R2=0.96-0.98, P<0.01), whereas the sensitivity with the random error was -0.47%/mm to -1.01%/mm ( R2=0.96-0.99, P=0-0.02). Conclusions:The dosimetric deviation of SBRT plan based on HD120 for lung cancer is highly sensitive to the anisotropic systematic error of leaf position, but less sensitive to the random error. In addition, the isotropic systematic error of leaf position will lead to the decrease of target coverage to a certain extent. Consequently, it is necessary to strictly control the systematic error of HD120 leaf position in the implementation of SBRT plan in clinical work.
ABSTRACT
Objective To analyze the failure and processing methods of helical tomotherapy multileaf collimator (MLC) and summarize relevant maintenance experience,aiming to accurately identify the faulty parts,shorten the downtime and enhance the work time.Methods The failure data of the helical tomotherapy MLC system in the past 48 months were analyzed to identify the common faulty parts,causes and processing methods.Results During the previous 48 months,the MLC failure occurred for 20 times,11 times for air compressor failure,4 times for position verification board failure,twice for leaf driver failure,twice for cushion valve failure and once for the slip of leaf position verification rod.The MLC failure was significantly correlated with the humidity of high-pressure gas.The work time of machine exerted significant effect upon the service time of MLC parts.Conclusions The structure of the helical tomotherapy MLC system is complex.The high-intensity work increases the failure rate.The humidity of high-pressure gas affects the normal operation of the MLC equipment.The faulty parts can be identified,the downtime can be reduced and the work time can be enhanced by summarizing the experience of MLC maintenance.
ABSTRACT
Objective To reduce the risk of radiation-induced cardiac injury in patients with left breast cancer after breast-conserving surgery by multileaf collimator (MLC) shielding technique.Methods A total of 18 patients with left breast cancer after breast conserving surgery were selected to obtain 3DCT and 4DCT images at free breathing state.The target area was identified on the 3DCT image by registration with 4DCT images and to develop a hybrid intensity-modulated treatment plan (H_IMRT) and a heart sparing hybrid intensity-modulated treatment plan (HSH_IMRT) to introduce MLC shielding technology to reduce the cardiac exposure dose,and to perform dosimetry verification of the treatment plan by using the Compass verification system.The prescription dose was 50 Gy in 25 fractions.The dosimetry parameters of the target area and the organs at risk were compared between the two treatment plans and the dose verification result.Results The result of the treatment plan showed that compared with H_IMRT,the dose uniformity of the target area of HSH_IMRT was better,and the difference of conformability was not statistically significant (P＞0.05).The mean dose of the whole heart decreased by 23.67％ (t =13.693,P＜0.05) compared with the former.Dmax and D of other substructures of the heart were lower than the former.The result of dose verification showed that there was no statistically significant difference in uniformity and conformity between the two planned target doses (P＞ 0.05).The mean dose of the whole heart of HSH_IMRT was 24.88％ (t =13.782,P＜0.05) lower than that of H_IMRT,and except for the left ventricle and right ventricle,the Dmax of other heart substructures and D of all heart substructures decreased.Both the planned and the dose verification result showed that the V20 and the D of the affected lung were lower in HSH_IMRT.Conclusions Reasonable introduction of MLC shielding technology in H_IMRT can reduce the exposure dose of cardiac and further reduce the risk of radiation damage in heart.
ABSTRACT
Objective To investigate the impact of four different collimator angle optimization techniques on the planning target volume (PTV) and organ at risk (OAR) during intensity-modulated radiotherapy (IMRT) for gastric cancer.Methods Ten patients with gastric cancer undergoing IMRT in Zhongnan Hospital of Wuhan University from 2015 to 2016 years were recruited in this study.All IMRT plans were designed by conventional five fields (330°,10°,45°,90°and 180°).In the Eclipse treatment planning system,four different collimator angle optimization techniques with consistent planning optimization parameters were employed to design the IMRT plan.Collimator angle optimization techniques included the following aspects.The collimator angle was set at 0 degree (CL0),collimator angle was set at 90 degree (CL90),Eclipse automatic collimator angle optimization (CLA) was adopted and collimator angle was set as the angle when the distance between X-Jaws and PTV (CLx) was the shortest.The dosimetric parameters mainly included the conformal index (CI) of PTV,the homogeneity index (HI),the mean dose (Mean),and the dosage of OAR.The treatment time (Time),monitor unit (MU),control point (CP),split field (SF) and conformal distance (Fx) were also considered.Results Regarding CL0 as the control,the CI,HI and Mean did not significantly differ among four collimator angle optimization techniques (all P＞0.05),whereas CLx could significantly increase the average dose of PTV in the target area (P＜0.05);CLx optimization reduced the liver (V30 reduction by 1.54％),left kidney (V12 decrease by 1.46％),right kidney and other OARs,whereas it slightly increased the maximum dose of the small intestine and spinal cord (＜1％).CLgo and CLA optimization elevated the dose of OAR in gastric cancer.Among four different collimator angle optimization techniques,CLx optimization reduced the MU (25.02％),CP (26.03％),Fx (20.27％) and SF (by 1.3separate fields on average) and treatment time (10.03％).CLgo and CLA optimization could decrease the MU,CP,Fx and SF.CL90 optimization had certain advantages in shortening the treatment time,whereas CLA optimization could prolong the treatment time by 5.04％.Conclusions During IMRT for gastric cancer,CL90,CLA and CLx collimator angle optimization techniques can obtain comparable dosimetry distribution to CL0 optimization technique,which can reduce the MU,decrease the radiation leakage,shorten the treatment time and improve treatment efficiency.
ABSTRACT
This thesis introduce the Multi-Leaf Collimator of Varian Linac,analyse the regular faults and show how to troubleshoot by every part.At the same time it introduce the daily maintenance of MLC and specific methods.
ABSTRACT
Objective To compare the sensitivity of Deha4 and ArcCHECK 3D detectors to detect the multi-leaf collimator (MLC) positioning errors in the dose verification of volumetric modulated arc therapy (VMAT) plans for nasopharyngeal carcinoma (NPC).Methods Ten NPC patients receiving VMAT plans were selected.The positioning error of 0.5-4.0 mm was introduced into the leaves of each MLC segment in the original file to expand,contract or shift the whole segments.The possible positioning errors of MLC in the treatment of VMAT were simulated.The Delta4 and ArcCHECK were utilized to verify the measurements.The absolute gamma passing rate was compared between the calculated dose and the measured dose of the VMAT plan by using the paired t-test.Results When the evaluation criterion was taken as 3 mm/3％,the absolute passing rate verified by the original plans of two detectors was greater than 95％.The positioning errors of MLC expansion,contraction and shifting detected by Delta4 and ArcCHECK were 1.5 mm,1.0 mm,2.0 mm and 3.0 mm,1.0 mm,and 3.0 mm,respectively.When taking 2 mm/2％ as the evaluation criterion,the absolute passing rate verified by the original plan was decreased significantly.Delta4 and ArcCHECK detected that the positioning errors of MLC expansion,contraction and shifting were 1.0 mm,1.0 mm,2.0 mm and 1.5 mm,0.5 mm,and 2.0 mm,respectively.Conclusions The dose verification of the VMAT plan for NPC by Delta4 and ArcCHECK can detect different types and sizes of MLC positioning errors,whereas the detection sensitivity slightly differs between Delta4 and ArcCHECK.Both of them are not sensitive to detect the MLC positioning errors less than 1.0 mm.It is fairly necessary to strengthen the quality assurance of MLC in the daily work.
ABSTRACT
PURPOSE: The treatment efficiency of ⁹⁰Y and providing reliable estimates of activity are evaluated by SPECT imaging of bremsstrahlung radiation released during beta therapy. In this technique, the resulting spectrum from ⁹⁰Y is very complex and continuous, which creates difficulties on the imaging protocol. Moreover, collimator geometry has an impressive effect on the spatial resolution, system sensitivity, image contrast, and the signal-to-noise ratio (SNR), which should be optimized.METHODS: We evaluated the effect of energy window width, reconstruction algorithms, and different geometries of a medium-energy (ME) parallel-hole collimator on the image contrast and SNR of ⁹⁰Y SPECT images. The Siemens E.Cam gamma camera equipped with a ME collimator and a digital Jaszczak phantom were simulated by SIMIND Monte Carlo program to generate the ⁹⁰Y bremsstrahlung SPECT images.RESULTS: Our results showed that optimal image quality can be acquired by the reconstruction algorithm of OS-EM in the energy window width of 60 to 400 keV for ⁹⁰Y bremsstrahlung SPECT imaging. Furthermore, the optimal values of the hole diameter and hole length of a ME collimator were obtained 0.235 and 4.4 cm, respectively.CONCLUSIONS: The acquired optimal ME collimator and energy window along with using a suitable reconstruction algorithm lead to improved contrast and SNR of ⁹⁰Y bremsstrahlung images of hot spheres of the digital Jaszczak phantom. This can improve the accuracy and precision of the ⁹⁰Y activity distribution estimation after radioembolization in targeted radionuclide therapy.
Subject(s)
Gamma Cameras , Signal-To-Noise Ratio , Tomography, Emission-Computed, Single-PhotonABSTRACT
This study proposed a method to calibrate tube focus spot and the center plane of rotation in computed tomography system. In the method, the tube was rotated to 0° and 180° respectively, and then one metal jig with symmetric windows A and B was scanned at each position under the tube cool and static condition. According to the geometry of tube focus spot, aperture center of the collimator and jig, the distance between tube focus spot and the center plane of rotation were calculated with the X ray transmittance data after denoising, mean value and normalization. To verify the practicability and validity of the method, the tube focus spot in a 16 slices CT system (Brivo CT385, GE, China) was calibrated, and the result after calibration was validated by scanning a polaroid film. The validation result showed that the deviation between tube focal spot and center plane of rotation was 0.02 mm and was in the error range within ± 0.1 mm. The results of this study showed that, as a simple and low-cost design, the method could be used for fast calibration between tube focus spot and the center plane of rotation.
Subject(s)
Calibration , Rotation , Tomography, X-Ray Computed , X-RaysABSTRACT
This paper introduces the failure phenomenon, failure analysis, maintenance process and method of SIEMENS PRIMUS linear accelerator.
Subject(s)
Particle Accelerators , Radiotherapy DosageABSTRACT
Objective To evaluate the accuracy and reliability of the CyberKnife VSI system for stereotactic radiotherapy.Methods First,the mechanical accuracy of the robotic manipulator system,the repeatability of the Iris variable aperture collimator system,the couch position accuracy of the patient positioning system,the tacking precision of the target locating system and the dosimetric beam characteristics of the linac system for each subsystem of CyberKnife VSI system were tested.Finally,the total beam delivery precision of the CyberKnife VSI system was evaluated.Results The mean positioning deviations of the mechanical arm movement of the robotic manipulator system were less than 0.1 mm,and the maximum positioning deviation of single note was ≤ 0.29 mm.The repeatability of the aperture sizes for the Iris variable aperture collimator system was ≤ 0.28 mm.The couch position accuracy of the patient positioning system was＜0.2 mm and the tracking precision of the target locating system was less than 0.5°.The linac beam-laser beam axes coincidence between the Iris and fixed collimators was better than 0.4 mm.The 6-MV beam parameters,such as beam quality and profile,were found within the acceptance limits.The deviations of output reproducibility,linearity and constancy versus linac orientation were less than 1.0％.The transmission factors of two types of collimators were lower than 0.4％.End-to-end test demonstrated that the maximum deviation of the total delivery precision of CyberKnife VSI system was 0.87 mm.Conclusion The CyberKnife VSI system is accurate and reliable for stereotactic radiotherapy.
ABSTRACT
Objective To construct and investigate the multi-leaf collimator (MLC) fault prediction model of Varian NovalisTx medical linear accelerator based on BP neural network.Methods The MLC fault data applied in clinical trial for 18 months were collected and analyzed.The total use time of accelerator,the quantity of patients per month,average daily working hours of accelerator,volume of RapidArc plans and time interval between accelerator maintenance were used as the input factors and the prediction of MLC fault frequency was considered as the output result.The BP neural network model of MLC fault prediction was realized by AMORE package of R language and the simulation results were validated.Results The model contained 3 layers of network to realize the input-output switch.There were 5 nodes in the input layer,13 nodes in the hide layer and 1 node in the output layer,respectively.The transfer function from the input layer to the hide layer selected the tansig function and purelin function was used from the hide layer to the output layer.The maximum time of training was pre-set as 150 in the designed model.Actually,111 times of training were performed.The pre-set error was 3％ and the actual error was 2.7％,which indicated good convergence.The simulation results of MLC fault applied in clinical trial for 18 months were similar to the actual data.Conclusions The BP neural network model realized by R language of MLC fault prediction can describe the mapping relationship between fault factors and fault frequency,which provides references for the understanding of accelerator fault and management of spare parts inventory.
ABSTRACT
One algorithm is designed to implement longitudinal auto-tracking of the the detector on X-ray in the digital radiography system (DR) with manual collimator. In this study, when the longitudinal length of field of view (LFOV) on the detector is coincided with the longitudinal effective imaging size of the detector, the collimator half open angle ( ), the maximum centric distance ( ) between the center of X-ray field of view and the projection center of the focal spot, and the detector moving distance for auto-traking can be calculated automatically. When LFOV is smaller than the longitudinal effective imaging size of the detector by reducing , the can still be used to calculate the detector moving distance. Using this auto-tracking algorithm in DR with manual collimator, the tested results show that the X-ray projection is totally covered by the effective imaging area of the detector, although the center of the field of view is not aligned with the center of the effective imaging area of the detector. As a simple and low-cost design, the algorithm can be used for longitudinal auto-tracking of the detector on X-ray in the manual collimator DR.