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【Objective】 To analyze the influence of different Inc parameters in the Monaco planning system on the left breast cancer volumetric modulated arc therapy (VMAT) planning, in the hope of providing some reference for plan design. 【Methods】 Seventeen left-breast cancer patients who were receiving radical radiotherapy were selected. The plans were enrolled in the design of VMAT with the same optimization conditions but different Inc parameters in the Monaco planning system. All plans used different Inc parameters like 10°, 20°, 30°, and 40°. The results of the plan were compared. The dosimetric parameters of the PTV and the organs at risk inquired by the plan were analyzed. The SPSS software was used for calculating the differences between the VMAT plans and evaluating the quality of the plans. 【Results】 The different Inc parameters affected the dosimetric parameters D98%, D2%, D50%, V55 Gy of PTV and CI, HI (F=10.528, F=15.154, F=15.513, F=16.979, F=4.632, F=14.277, all P<0.05). The MU of the four groups significantly differed (F=4.632, P<0.05), and the difference of V10 on the ipsilateral lung was significant (F= 3.324, P<0.05), the remaining parameters in the four groups had no statistically significant difference. 【Conclusion】 For the left-breast cancer volumetric modulated arc therapy, the smaller of Inc parameter on the plan had better dose distribution and conformity index while the monitor units increased. 40° was not suitable for the breast cancer VMAT plan, and the high amount beyond the range would increase the toxic and side effects on the skin.
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Objective To investigate the impact of actual gantry angle on the accuracy of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods A total of 27 patients with NPC were enrolled in this study. IMRT plans were designed with Pinnacle treatment planning system (TPS),and 8 beams with an interval of 30°(within 0°-360°) were selected for each plan. These plans were divided into plan A and plan B according to the beam parameters. In plan A,the minimum sub-field area was 5 cm2 ,the minimum number of sub-field monitor unit ( MU) was 5,and the maximum sub-field number was 80;in plan B,the minimum sub-field area was 8 cm2 ,the minimum number of sub-field MUs was 8,and the maximum sub-field number was 60.The gamma passing rate using the criteria of 3%/3 mm and 2%/2 mm at actual and zero degree gantry angles were calculated using Mapcheck 2 device for dose verification,and were compared with the paired t-test. The relationship between the above differences (Δ value) and the beam angle or the beam parameters was also analyzed. Results In plan A with the criteria of 3%/3 mm, the beams were significantly different (P=0000-0007) except for at angles of 270°,300°,and 300°,and the mean Δ value was 090%;under the criteria of 2%/2 mm,all beams were significantly different ( P=0000-0019) except for at an angle of 300°,and the meanΔvalue was 272%.In plan B with the criteria of 3%/3 mm,the beams showed no significant difference ( P=0052-0639) except for at an angle of 300 ° ,and the mean Δ value was 040%;under the criteria of 2%/2 mm,all beams showed no significant difference ( P>005) except for at angles of 210°,240°,270°,and 300°,and the meanΔvalue was 152%.When the plan B parameters were used, the Δ value was reduced;the results of two verification methods were more consistent,so the accuracy was also improved. Conclusions Compared with the validation method at zero degree gantry angle,the validation method at an actual gantry angle is associated with reduced gamma passing rate because of some factors such as gravity,which is not significantly related to the beam angle,but the beam parameters. In the design of IMRT plans for NPC,the total number of sub-fields should be decreased as far as possible,and the minimum sub-field area and the minimum number of MU should be increased, so as to improve the accuracy of treatment plans.
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Objective To investigate the impact of actual gantry angle on the accuracy of intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods A total of 27 patients with NPC were enrolled in this study. IMRT plans were designed with Pinnacle treatment planning system (TPS),and 8 beams with an interval of 30°(within 0°-360°) were selected for each plan. These plans were divided into plan A and plan B according to the beam parameters. In plan A,the minimum sub-field area was 5 cm2 ,the minimum number of sub-field monitor unit ( MU) was 5,and the maximum sub-field number was 80;in plan B,the minimum sub-field area was 8 cm2 ,the minimum number of sub-field MUs was 8,and the maximum sub-field number was 60.The gamma passing rate using the criteria of 3%/3 mm and 2%/2 mm at actual and zero degree gantry angles were calculated using Mapcheck 2 device for dose verification,and were compared with the paired t-test. The relationship between the above differences (Δ value) and the beam angle or the beam parameters was also analyzed. Results In plan A with the criteria of 3%/3 mm, the beams were significantly different (P=0000-0007) except for at angles of 270°,300°,and 300°,and the mean Δ value was 090%;under the criteria of 2%/2 mm,all beams were significantly different ( P=0000-0019) except for at an angle of 300°,and the meanΔvalue was 272%.In plan B with the criteria of 3%/3 mm,the beams showed no significant difference ( P=0052-0639) except for at an angle of 300 ° ,and the mean Δ value was 040%;under the criteria of 2%/2 mm,all beams showed no significant difference ( P>005) except for at angles of 210°,240°,270°,and 300°,and the meanΔvalue was 152%.When the plan B parameters were used, the Δ value was reduced;the results of two verification methods were more consistent,so the accuracy was also improved. Conclusions Compared with the validation method at zero degree gantry angle,the validation method at an actual gantry angle is associated with reduced gamma passing rate because of some factors such as gravity,which is not significantly related to the beam angle,but the beam parameters. In the design of IMRT plans for NPC,the total number of sub-fields should be decreased as far as possible,and the minimum sub-field area and the minimum number of MU should be increased, so as to improve the accuracy of treatment plans.
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PURPOSE: In order to keep the acceptable level of the radiation oncology linear accelerators, it is necessary to apply a reliable quality assurance (QA) program. MATERIALS AND METHODS: The QA protocols, published by authoritative organizations, such as the American Association of Physicists in Medicine (AAPM), determine the quality control (QC) tests which should be performed on the medical linear accelerators and the threshold levels for each test. The purpose of this study is to increase the accuracy and precision of the selected QC tests in order to increase the quality of treatment and also increase the speed of the tests to convince the crowded centers to start a reliable QA program. A new method has been developed for two of the QC tests; optical distance indicator (ODI) QC test as a daily test and gantry angle QC test as a monthly test. This method uses an image processing approach utilizing the snapshots taken by the CCD camera to measure the source to surface distance (SSD) and gantry angle. RESULTS: The new method of ODI QC test has an accuracy of 99.95% with a standard deviation of 0.061 cm and the new method for gantry angle QC has a precision of 0.43degrees. The automated proposed method which is used for both ODI and gantry angle QC tests, contains highly accurate and precise results which are objective and the human-caused errors have no effect on the results. CONCLUSION: The results show that they are in the acceptable range for both of the QC tests, according to AAPM task group 142.
Subject(s)
Particle Accelerators , Quality Control , Radiation OncologyABSTRACT
Objective To study corrective method for displacement in the procedure of electronic portal imaging device (EPID)-based intensity-modulated radiotherapy dose valuation by studying the relative mechanical displacement of different vendor EPID (aS1000,Varian; aS500,Varian; iViewGT,Elekta).Methods A 5 cm × 5 cm field was set up to acquire portal images for three kinds of EPID,then a in house software was used to analysis the portal images.The relative displacement was acquired via analyzing a series of comparation between center positions of gantry angle ranging from 0° to 360° and gantry angle at 0°.Results In the lateral direction,the maximum relative displacement of EPID with aS1000,S500 and iViewGT were (-0.23 ±0.17) mm,(2.94±0.17) mm and (0.35 ±0.09) mm,respectively.In the longitude direction,the displacements were (-4.16 ± 0.20) mm,(-4.15 ± 0.25) mm and (-1.66 ±0.11) mm,respectively.As to longitude direction,the displacements could be well fitted with the usage of quadruplicate empiric function.Conclusions There is a significant difference at the aspect of relative displacement between different vendors EPID at different gantry angles.And the displacement in the longitude direction is obviously larger than in the lateral direction.The relative displacement should be corrected when applying EPID to the intensity-modulated radiotherapy dose verification at different gantry angles.
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Objective To investigate the impact of accelerator′s multi-leaf collimator (MLC) on the radiotherapy dose with different gantry angles.Methods Measured with Mapcheck 2D diode array and 30 cm×30 cm×3 cm solid water, Pre-selecting the 30 appropriate single fields and 0°,45°,90°,270°,315° gantry angles of static and dynamic intensity modulated radiation therapy (IMRT), quantification analysis of the passing rate with MapCheck γ(3%/3 mm) and (5%/3 mm) analysis methods, and the same method to 30 examples static and dynamic IMRT plans.Results When the accelerator collimator angle is 0°,the 30 appropriate single fields′ passing rate of between 0°gantry angle and 45°,90°,270°,315°gantry angles of static and dynamic IMRT accordingly is 97.71% and 96.25%(t=1.70, P=0.389), 96.34% and 93.72%(t=2.95, P=0.002), 96.65% and 92.98%(t=2.87, P=0.005), 95.87% and 93.15%(t=2.71, P=0.006), 96.09% and 93.51%(t=2.89, P=0.004) with MapCheck γ(3%/3 mm) analysis methods, however, the passing rate also does not have the difference, respectively is 99.31%-99.73% and 98.89-99.68%(t=0.57-1.90, P=0.913-0.725) with MapCheck γ(5%/3 mm) analysis methods;the passing rate of 30 examples static and dynamic IMRT plans accordingly is 96.11%-96.76% and 94.88%-95.78%(t=1.02-1.61, P=0.317-0.235).Conclusions When the accelerator collimator angle is 0°, at different gantry angles, MLC leaves due to gravity, friction, inertia, etc caused by errors in place, the physical penumbra and leakage radiation will indeed affect the IMRT dose, however, the deviation of dose distribution is within acceptable 5%.
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Objective To study the impact of accelerator's gantry angle on MLC position accuracy. Methods Kodak X-omat-V Films were used, appropriate multi-leaf collimator positions and gantry angles were chosen, precise setup was needed , and the exposal films were analyzed by RIT113 software. Results At all conditions, most of the leaf position errors were less than 0. 5 mm. There were 2 pairs of leaf position errors larger than 1 mm when the gantry angle was 270° and the leaves moved from left to right. Conclu-sions Gantry angle can affect the accuracy of multi-leaf collimator position. Gravity and inertia increase the uncertainty of leaf position accuracy. Prieise setup is critical for the dose measurement.
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For evaluating the lumbar disc space, the fact that the postmyelography computed tomography was more accurate than computed tomography or myelography is well-known. But the technical difficulty is limitation of gantry angle. The prone position scanning may help to lessen this trouble. A prospective computed tomographic scanning was performed in both the prone and supine position on 43 patients, who had low back pain. The angle between the vertebral end plate and vertical line was measured in both position at L3-4, L4-5 and L5-S1 interspaces. The advantages of prone scanning in spinal aligment was noted at L5-S1 disc space(79.1%) and also more desirable if computed tomography was performed with metrizamide. With above advantages, the evaluation of bulging annulus was became more easier.