Complexity score-based plan quality control of VMAT / 中华放射肿瘤学杂志

Objective:To explore the difference in the complexity of different treatment planning systems, multi-leaf collimator (MLC) types and treatment sites of volume-modulated arc therapy (VMAT), and propose a complexity score for plan quality control.Methods:Statistical analysis of 12 complexity metrics including Monaco and Eclipse, Agility, Millennium and High-definition MLC, nasopharyngeal, lung and cervical cancer was performed. Spearman correlation coefficient between complexity metrics was calculated. Principal component analysis was conducted to reduce the dimensionality of the original data set to the first two principal components and explain its physical meaning. Complexity score based on the principal components was calculated to establish warning and action thresholds for plan quality control. The correlation between complexity metrics and γ pass rate was analyzed.Results:Except cervical cancer aperture sub-regions metric, other metrics had significant differences between Monaco and Eclipse. Monaco MLC had a more regular field but higher MU, smaller leaf gap, and longer leaf travel distance. High-definition MLC with smaller leaf width significantly added MLC aperture-related metrics. The first two principal components explained over 80% of the total variance of the original dataset, complexity score was weighted average of first two principal components. The distribution of complexity score for different equipment and sites was different. The warning threshold was expressed as the average plus standard deviation, and the action threshold was expressed as the average plus 2 standard deviations. Complexity metrics and complexity scores had small correlation with γ pass rate, showing weak or irrelevant but statistically significant. Conclusions:Different planning systems, MLC types, and treatment site complexity metrics are significantly different. The complexity score is a useful tool for plan quality control.

Evaluation the combined effect of three dose reconstruction systems on VMAT dosimetry verification of lung cancer / 中华放射肿瘤学杂志

Objective:To evaluate the combined effect of an trajectory log field based(LBF)and two commercial dose reconstruction systems on volume-modulated arc therapy(VMAT)dose verification of lung cancer.Methods:An in-house program was developed to introduce errors in trajectory log of TrueBeam to the origin plan and recalculate the dose of the error plan in treatment planning system(TPS). A total of 18 lung cancer cases treated by two-arc VMAT were selected to perform on LINAC and measured by ArcCheck simultaneously. Then, the reconstructed doses were obtained by 3DVH. The mode of reconstruction was calculated by LFB and Compass. Five of the 18 cases were performed on LINAC two times in four hours and measured by ArcCheck to evaluate the stability of the TrueBeam performance. The 18 plans were recalculated and performed on LINAC with a solid water phantom with 5 cm build-up, 4 cm back scattering thickness and a FC65-G detector in the center. The measured dose by detector was compared with the reconstructed dose by three systems.Results:TheTruebeam performance was stable. For all of the 18 cases, the point dose measured by FC65-G and reconstructed by three systems had a deviation of less than 2% to the TPS calculated. For all of the organs reconstructed by LBF and most organs reconstructed by 3DVH and Compass, the γ pass rate between them and TPS all exceeded 90% under all criteria, as well as the ArcCheck measured results. For all the organ dose difference between reconstructed and TPS, LBF system had the smallest difference, followed by the Compass system except the lung, and the 3DVH had the highest difference.Conclusions:LBF, 3DVH and Compass can reflect the VMAT dose verification results of lung cancer from different perspectives. The combined application of three systems can demonstrate the verification results in an intuitive manner, which is beneficial for subsequent analysis.

The impact factors of longitudinal dose fall-off outside the target with helical tomotherapy / 中华放射医学与防护杂志

Objective:To study the changing characteristics and impact factors of helical tomotherapy (HT)for longitudinal dose fall-off outside the target, in order to guide the plan junction or pretreatment target and implementation efficiency in clinical.Methods:Eight patients with head and neck tumors admitted to the Department of Oncology Radiotherapy of the First Affiliated Hospital of Zhengzhou University in December 2019 were retrospectively selected as the research objects. The planning target area and dose drop structure were outlined in the head and neck images with a thickness of 1 mm obtained by Siemens SOMATOM Definition AS positioning computerized tomography (CT). Different field widths (FW, 5.0 cm/2.5 cm/1.0 cm) and pitches (0.430/0.287/0.215) were assembled for planning with the same modulation factor (1.8), finest does calculation grid (0.195 cm ×0.195 cm) and other planning parameters were consistent. The plans were designed by different parameters, and the result was analyzed by univariate analysis.Results:The that different pitch curves coincided under the same field width by comparative analyzing, so pitchs had no effect on dose drop. The different field width curves were independent of each other, indicating that the field width had an effect on dose drop in the head and foot direction. The relationship between the longitudinal dose drop speed outside the target and the change of the field width was inversely correlated: the larger field widths meant the slower dose fall-off and the larger penumbra, while the smaller field widths meant the faster fall-off and the smaller penumbra. When the dose fall-off to 50% of the prescribed dose, the distance from the target was approximately equal to half the field widths, and the pitchs had not affect the rate of dose-drop, while the dose at different distances from the target boundary could be calculated by the fitting formulas. The field widths and pitchs had little effect on the CI and HI index of the target, relatively, the target area was best when the field width was 2.5 cm. The total beam-on time gradually decreased with the increase of the field widths and pitches.Conclusions:When segment target therapy needs to consider planning junction, execution efficiency, and controlling longitudinal dose fall-off and considered the execution, the optimal planned parameters such as field widths and pitches could be selected or the target at the junction regions could be adducted according to the longitudinal dose drop formula, so as to achieve the ideal dose distribution.

Evaluation of multi-leaf collimator performance of TrueBeam accelerator using high-resolution trajectory log files / 中华放射肿瘤学杂志

Objective:To evaluate the multi-leaf collimator (MLC) performance of TrueBeam accelerator using trajectory log files.Methods:All tests were performed 5 times under different gantry-collimator angle combination. The 1 mm picket fences were constructed by static or dynamic MLC. The control ability for small-field accuracy of accelerator was evaluated. Repeatability was assessed by MLC repeat motion. The movement performance of difference velocities along one direction and the opposite direction were evaluated via a 1 cm picket fences which slipped from -7 cm to 7 cm with a uniform velocity and stopped or immediately back at 7 cm. The MLC performance in a complex program was evaluated by a cross movement test.Results:Both the static and the dynamic picket fences yielded high accuracy. The deviation spectrums of MLC in different gantry angle were consistent, however, an absolute difference of 0.001 1 mm was found. For uniform velocity movement tests with 0°gantry, the RMSE of MLC was increased from 0.015 0 mm to 0.059 8 mm when the speed was accelerated from 5 mm/s to 25 mm/s. Similar results were obtained in non-zero gantry angle. The "overspeed" effect caused by the direction change movement of MLC was less obvious than that caused by speed changed from zero to a uniform velocity movement state. There was no significant change in speed before and after the MLC crossing. The MLC speed fluctuated around the set value, which was independent of the gantry angle.Conclusion:A method for evaluating the performance of MLC using trajectory log files is established, which can evaluate the MLC performance of TrueBeam accelerator and be used for MLC rapid quality control in clinical practice.

A quantitative evaluation on the image-quality parameters and quality assurance thresholds setting of accelerator on-board imaging system / 中华放射肿瘤学杂志

Objective@#To achieve quantitative analysis of image quality parameters and establish warning and action thresholds for the on-board imaging (OBI) system of linear accelerator.@*Methods@#The Catphan604 phantom was repeatedly scanned in the Full-Fan and Half-Fan CBCT scanning modes on a Varian EDGE linear accelerator, and the software based on Python language development in-house was utilized to analyze image quality parameters, such as CT number linearity, geometric consistency, slice thickness, spatial resolution, uniformity and low-contrast resolution. The quantitative analysis results of each image quality parameter obtained from 16 times of scanning within 16 months were normalized to the mean and the standard deviations were recorded. A run chart analysis was created to determine the warnings and action thresholds.@*Results@#The software built in-house can quantitatively analyze the image parameters of the two scanning modes of OBI system. The low-contrast resolution of Half-Fan was better than that of Full-Fan, whereas the spatial resolution of Full-Fan was superior to that of Half-Fan. One standard deviation (1σ) was set as the warning threshold and 2 standard deviations (2σ) as the action threshold, respectively. The tolerance level of Half-Fan was smaller than that of Full-Fan.@*Conclusion@#Self-developed software enables quantitative analysis of accelerator image quality parameters, establishes warning and action tolerance of quality assurance and provides guidance for image quality assurance under image-guided radiotherapy specification.

Commissioning and testing of treatment planning system model of an Edge accelerator with a high-definition multi-leaf collimator / 中华放射肿瘤学杂志

Objective To investigate the commissioning and testing of the Eclipse model of an Edge accelerator with high-definition muhi-leaf collimator (HD-MLC).Methods The percentage depth dose (PDD),profile,output factor measured by Razor and CC13 were statistically compared with the standard data.Penumbra,transmission factor (TF),leakage,concave-convex groove,accuracy of movement and dosimetry leaf gap (DLG) were measured with EBT3,electronic portal image device (EPID) and PTW SRS1000&SRS1500.The optimal DLG/TF was acquired when the γ pass rate of test cases was the highest.The point dose of regular fields,intensity-modulated radiation therapy (IMRT) and volume-modulated radiation therapy (VMAT) was verified with FC65-G.The planar dose of these case was verified with Octavius 4D and EBT3.Results The measured PDD data were consistent with the standard data.The measured penumbra of 3 cm and 4 cm square fields was smaller,whereas that of 6 cm square field was larger than the standard values.The left and right edge,field size,center of the field were distributed within the range of-1.0-0.4 mm、0.2-1.7 mm,-0.3-1.9 mm and-0.1-0.8 mm,respectively.The mean penumbra of the left and right MLC in different positions were (2.5±0.042) mm and (2.7±0.005) mm.The leakage of MLC was 0.009-0.016.The measured DLG/TF was 0.1861 cm/0.0116 and the optimal DLG/TF was 0.015 cm/0.014.The differences of point dose of all the test cases except the one which was in the low-dose area were within ±3％.Local and global γ pass rates of all IMRT were 79.81％-100％ and 96.3％-100％ (3％/3 mm),71.3％-98.9％ and 94.3％-99.8％ for VMAT cases.Conclusions This method can accurately test and commission the Eclipse treatment planning model of Edge Linac equipped with HD-MLC.

Impact factors of dose distribution in the abutment area duing total body irradiation with helical tomotherapy / 中华放射医学与防护杂志

Objective To investigate the optimal distance between upper and lower target volumes and their correlated planning parameters by analyzing the dose distribution in the abutment regions during total body irradiation ( TBI) using helical tomotherapy. Methods A total of 10 patients with acute leukemia and with a height around 120 cm were enrolled. All patients were scanned by a Siemens simulation computerized tomography (CT) at a slice thickness of 5 mm. A lead wire was placed 10. 0 cm above the patella as a marker of the separation boundary for the upper and lower target volumes. The delineations of target volumes and organs at risk ( OARs ) were performed in the Varian Eclipse 13. 5 workstation with targets shrunk beyond the separation boundary at different distances. After contours and CT images were transferred to HT workstation, treatment plans were designed with different field width (FW, 5. 0 cm/2. 5 cm/1. 0 cm) and pitch values (0. 430/0. 287) at a modulation factor of 1. 8. All the plans were optimized with a dose calculation grid of 0. 195 cm × 0. 195 cm and identical planning parameters. The correlation between treatment planning parameters and targets shrunk distances were investigated by analyzing the dose distributions in the abutment area. Results The study demonstrated that the dose distributions in the abutment area were influenced only by the field width parameters: when the gap distance between the upper and lower targets was 5. 0 cm, the optimal FW is 5. 0 cm;Similarly when the gap distances were 2. 0 cm and 1. 0 cm, and the optimal FW 2. 5 cm and 1. 0 cm, respectively. In another words, the dose distribution of the abutment region was optimal when the target gap distance was equal to FW. Pitch values did not affect the quality of dose distribution in the abutment region and the overall treatment time ratio. Overall treatment time was inversely related to the FW. Conclusions Consistent target distance and FW is helpful to improve the dose homogeneity in the abutment area during TBI with HT. Appropriate planning parameters is critical to balance the treatment efficacy and efficiency.

Accurate speech segmentation via the improved short-time fractal dimension / 西安交通大学学报·英文版

Objective: To improve the accuracy of speech segmentation through the improved short-time fractal dimension. Methods: An equation was established for window size selection of speech analysis. Dynamic Window Step (DWS), a novel method to determine the sliding window steps adaptively in agreement with the local properties of signals, was proposed. Results: The influence of the window step on the short-time fractal dimension was discussed. Compared with fixed window steps, more accurate and efficient fractal dimension trajectories were obtained with dynamic window steps. Conclusion: The proposed method was applied to a number of speech signals. It shows promise in speech segmentation, speech recognition and other transient signal analysis.