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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.
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Objective To establish and evaluate a morning check system for linac based on electronic portal image device (EPID).Methods Delivered fluence maps of open and wedge fields at 10 cm×10 cm field size of Synergy Linac were measured by EPID.Figure features from these two images were extracted with matlab codes and analyzed to realize a quick morning check.The repeatability of dose response and mechanical setup,relationship between gray value and machine unit (MU),accuracy of output and field size test were investigated with both EPID and DailyQA3.The status of Synergy linac was monitored both by DailyQA3 and EPID for two months.Results EPID was able to test the linac consistently with a testing error of 0.50 mm,1.00 mm for field size and center,respectively.Both of the test accuracy for flatness and symmetry was 0.17％.The mechanical accuracy test and dosimetric repeatability test were also consistent.The dose response of EPID was linearly related to the linac output (R2＞0.999).EPID was highly sensitive to the change of output and radiation field size.The measurement deviations between EPID and DailyQA3 were consistent and within clinical acceptable tolerance.Conclusions EPID showed great accuracy and stability on monitoring the performance of linac.The established daily check tool based-on EPID is accurate and reliable for clinical usage.
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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.
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Objective To explore the dosimetric difference between different radiotherapy technologies in the treatment of early peripheral stage non?small ?cell lung cancer ( NSCLC ) . Methods Four?dimensional computed tomography scans and delineation of target volumes and organs at risk ( OARs) were performed in 5 patients pathologically diagnosed with stage T1/T2 peripheral NSCLC who were admitted from 2014 to 2015. Target volumes contained gross tumor volume (GTV), internal target volume (ITV), and planning target volume (PTV). ITV was contoured on the maximum intensity projection images. PTV was defined as ITV plus a 5 mm margin. OARs contained the heart, lung, esophagus, and spinal cord. The Monaco 5. 0 treatment planning system was used to design three plans. The three?dimensional conformal radiotherapy (3DCRT) plan had 11 fields in the diseased lung covering the PTV plus a 0. 2 cm margin. The sliding window intensity?modulated radiotherapy ( SW?IMRT ) plan had 9 fields in the same areas as the 3DCRT plan. The volumetric modulated arc therapy ( VMAT) plan had the gantry rotating 180° around the diseased lung. The evaluation criteria referred to the RTOG 0618 trial. Comparison was made by paired t test. Results The SW?IMRT plan had a significantly better homogeneity index than the 3DCRT plan ( 1. 03 vs. 1. 24,P= 0. 017 ) . Compared with the VMAT plan, the mean monitor units in the 3DCRT plan was significantly reduced by 24. 5%( P=0. 022) . The V30 and V40 of the 3DCRT plan were significantly reduced by 29. 4% and 28. 4%, respectively, compared with the SW?IMRT plan ( P=0. 003,0. 006) and 56. 7%and 59. 7%, respectively, compared with the VMAT plan ( P=0. 041,0. 019) . Conclusions 3DCRT may be an appropriate radiotherapy method for early stage NSCLC.