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Objective:To analyze the attenuation of immobilization baseplate of carbon fiber for ray and the change of dose verification results for enhanced radiation field of MatriXX. And to primarily research the influence of this immobilization baseplate for the dose distribution of radiation field of radiotherapy.Methods: 20 patients with cervical cancer were enrolled in the research. The angle of gantry was 180°in the enhanced plan of immobilization field, and the corresponding verification plans were designed. When the verification plan was implemented on the Varian Clinac iX of accelerator, the two-dimensional ionization chamber array (MatriXX) was used to measure dose distributions of the plan. The immobilization baseplate of carbon fiber (ORFIT AIO) was used in the research. The situations of no baseplate (A group), one baseplate (B group), two baseplates (C group)and three baseplates (D group)between the handpiece of accelerator and Matri XX were researched, respectively. The data of the 4 groups were obtained by using software (OminiPro I'mRT), and the largest dose point and passing rate of Gamma in plane of radiation field were counted and analyzed.Results: Compared with A group, the average attenuation factors for ray on the largest dose point of B, C and D group in the plane of radiation field were (1.73±0.11)％, (3.44±0.36)％, and (5.48±0.44)％, respectively. The passing rates of Gamma in the 4 groups were (94.87±2.31)％, (99.18±0.61)％, (99.79±0.27)％ and (96.24±1.99)％, respectively. And the differences of passing rate between each group and A group were statistical significance (t=9.788,t=9.261,t=2.256,P<0.05).Conclusion:The immobilization baseplate of carbon fiber has influence for the attenuation of high-energy X-rays and it can affect the dose distribution of radiation field which has passed baseplate in some degrees. And when physicists calculates the dose, they should consider the effect of immobilization baseplate of carbon fiber for dose distribution of radiation field.
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Objective To compare the dosimetric verification results of Varian Portal Dosimetry and Matrixx,and to assess the reliability of the clinical application of electronic portal imaging device (EPID) verification.Methods Varian TrueBeam linear accelerator,which was equipped with a 120-leaf multileaf collimator and an amorphous silicon EPID,as well as portal dose prediction software.IBA I′mRT Matrixx ion chamber array was used.EPID algorithm configuration,dose calibration,and testing before use were performed.The sliding-window protocol was used.There were 77 patients with tumors involving the head and neck (mainly nasopharyngeal carcinoma),mediastinum,abdomen,and pelvic cavity were selected.The verification plan of the portal dose was created with a source-detector distance of 100 cm,and the gantry angle was kept the same as the treatment plan.The verification plan was carried out in the TrueBeam machine,and the data were collected at the same time by EPID.Comparison between the measured and calculated dose images was performed,and the evaluation standard was gamma index (3%/3 mm).The paired t-test was used for difference analysis.Results For the 77 patients,the Gamma passing rates of both methods were above 97%.Except for head and neck carcinoma were a significant difference between the results of dosimetric results using EPID and Matrixx in intensity-modulated radiotherapy (P=0.018) other remaining all P> 0.05.Conclusions The dosimetric verification results of EPID are consistent with those of Matrixx.EPID can be used for dosimetric verification,and Matrixx ion chamber array can be used only in case of a low Gamma passing rate.
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Objective To compare IMSure QA and MatriXX for intensity modulated radiotherapy plans,and to investigate the credibility of IMSure QA software.Methods Ten patients receiving intensity modulated radiotherapy were randomly chosen for the quality assurance plans with IMSure QA and MatriXX.Results The overall average of percentage pass points in 3％ and 3 mm were (98.1 ± 0.8) ％ with IMSure QA,and (97.9 ±0.6)％ with MatriXX(t =0.86,P ＞0.05).Conclusion IMSure QA can be a reliable verification tool for IMRT QA.
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Objective To explore the MatriXX measurements the dose distributions for each beam in intensity-modulated radiotherapy (IMRT) plans were measured with 0 degree gantry angle and actual gantry position respectively.To discuss whether the two multi-angle synthetic pass rate from the two methods has statistics differences.Methods The dose distributions for each beam in IMRT plans were measured with 0 degree gantry angle and actual gantry position for twelve patients with head and neck tumor respectively.The γ pass rates (according to 3％/3 mm) for each beam under each angle condition was obtained by the comparison between the measured and the calculated dose distributions from the treatment planning system which was treated as the reference distribution.Use the t-test to analyse the actual gantry angle method and use the one factor analysis of variance to analyze the two multi-angle synthetic pass rate from the two methods.Results The γ pass rates of actual gantry angle was found generally declined seemingly compared with 0 degree gantry angle,but differentγ pass rates showed only in 80 °,120°and 240° with98.71％,93.59％(t=2.10,P=0.000),98.15％,93.17％ (t=2.10,P=0.000) and 98.94％,92.85％ (t =2.10,P =0.000) respectively.The γpass rate of multi-angle synthetic was seemingly between methods (98.27％,94.63 ％,F =0.50,P =0.134).Conclusions Two kinds of IMRT verification mode are from two position to validated the IMRT plans dose accuracy,comparatively analysing the conclusions drawn from the two methods can protect accuracy of IMRT plans more comprehensively.
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Objective To characterize angular dependency of MatfiXX and develop a method for its calibration in order to verify treatment plan with original gantry angles.Methods Absolute dose calibration was carried with thimble ionization chamber on the linear accelerator.so as to make sure 1 MU=1 cGy at the depth of maximum dose(dmax).A MatriXX was put into a Mutlicube phantom,and the ionization chamber matrix was calibrated with absolute dose.In order to determine a correction factor CF as a function of gantry angle θ.open beam fields of 10 cm×10 cm size were irradiated for gantry angles θ=0°-180°(every 5°)and every 1°for lateral angles θ in the range of 85°-95°.CF was defined as the ratio of the dose measured with ionization chamber and the dose from MatriXX.Results Relatively large discrepancies in response to posterior VS.anterior fields for MatriXX detectors(up to 10%)were found during the experiment and relatively large variability of response as a function of gantry angle.The pass rate of treatment plan in lateral beams was lower than that of other beams.The isodose distribution of corrected MatriXX matched well with the outcome from the treatment planning system. Conclusions The angular dose dependency of MatriXX must be considered when it is used to verify the treatment plan with original gantry angles.
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Objective To investigate the features of 2-D air vented ionization chamber array MatriXX system to use the QA procedures of radiotherapy. Methods Some important QA procedure of clinical radiotherapy practice were investigated by using a MatriXX system and a phantom made in house, mainly including the calibration of MatriXX, the off-axis rate (OAR) of virtual wedge fields, the connection between two half-fields or two asymmetry-fields, the skillful adjustment of the clinac flat filter, the 2-D dose distribution verification of radiotherapy planning, the influence of scatter screen to a large area electron beam field, the effect and best thickness and shielding position of block for a large area electron beam fields with scatter screen. Results The OAR of any virtual wedge field can be measured by a MatriXX system in a single irradiation. The conjunction accuracy of two half-fields or two asymmetry-fields may be less than 1 ram. The difference between the calculated and measured dose of any point or any isodose or any OAR of a field can be determined by using a MatriXX system. After the adjustment of the elinae flat filter with the help of MatriXX system, the flatness and symmetry of the field are 1. 85 % and 0.98 %, respectively. The dose characteristic of a large area electron beam field may be distinctively influenced by a scatter screen, and under this condition, the block faraway from the shielded target can hardly protect the organ at risk, and directe block which is put on or near the organ at risk is perfect. Conclusion Compared with conventional ionization chamber (Farmer type) or film dose measuring, the MatriXX combined with the OmniPre I'mRT software is much more convenient and effective in QA practice of clinical radiotherapy, and it's a perfect tool for the QA procedure of radiation therapy.
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PURPOSE: To compare the accuracy and efficacy of EDR2 film, a 2D ionization chamber array (MatriXX) and an amorphous silicon electronic portal imaging device (EPID) in the pre-treatment QA of IMRT. MATERIALS AND METHODS: Fluence patterns, shaped as a wedge with 10 steps (segments) by a multi-leaf collimator (MLC), of reference and test IMRT fields were measured using EDR2 film, the MatriXX, and EPID. Test fields were designed to simulate leaf positioning errors. The absolute dose at a point in each step of the reference fields was measured in a water phantom with an ionization chamber and was compared to the dose obtained with the use of EDR2 film, the MatriXX and EPID. For qualitative analysis, all measured fluence patterns of both reference and test fields were compared with calculated dose maps from a radiation treatment planning system (Pinnacle, Philips, USA) using profiles and gamma evaluation with 3%/3 mm and 2%/2 mm criteria. By measurement of the time to perform QA, we compared the workload of EDR2 film, the MatriXX and EPID. RESULTS: The percent absolute dose difference between the measured and ionization chamber dose was within 1% for the EPID, 2% for the MatriXX and 3% for EDR2 film. The percentage of pixels with gamma%>1 for the 3%/3 mm and 2%/2 mm criteria was within 2% for use of both EDR2 film and the EPID. However, differences for the use of the MatriXX were seen with a maximum difference as great as 5.94% with the 2%/2 mm criteria. For the test fields, EDR2 film and EPID could detect leaf-positioning errors on the order of -3 mm and -2 mm, respectively. However it was difficult to differentiate leaf-positioning errors with the MatriXX due to its poor resolution. The approximate time to perform QA was 110 minutes for the use of EDR2 film, 80 minutes for the use of the MatriXX and approximately 55 minutes for the use of the EPID. CONCLUSION: This study has evaluated the accuracy and efficacy of EDR2 film, the MatriXX and EPID in the pre-treatment verification of IMRT. EDR2 film and the EPID showed better performance for accuracy, while the use of the MatriXX significantly reduced measurement and analysis times. We propose practical and useful methods to establish an effective QA system in a clinical environment.