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Objective To evaluate the dosimetric characteristics of the TomoDose diode and its application in detecting the couch velocity and assessing the beam Profile stability for convenient and efficient quality control of Tomotherapy.Methods Fundamental properties of the TomoDose detector,such as dose linearity,dose per pulse dependence,directional dependence and field size dependence were tested by the water-equivalent phantom and the results were statistically compared with those measured by the ion-chamber (0.057 cm3,A 1SL).Five different couch velocities with a time interval of 0.0005 s were designed to test the sensitivity of TomoDose for detecting the couch velocity,and then the clinical data of 7 patients with different couch velocities were selected to verify the test accuracy.The beam profile of three different jaws of 1.0,2.5 and 5.0 cm were measured using TomoDose with water-equivalent phantom in the x and y directions under the same conditions as water tank with an underwater depth of 15,50,100,150 and 200 mm,respectively.The Profile data obtained by water tank and TomoDose were evaluated using the Gamma (γ) evaluation method with the 2％/1 mm criterion.Results The dose linearity of the TomoDose and ion chamber was in a linear pattern within the beam-on-time ≤ 30 s.The difference between the TomoDose and ion chamber was less than 2％ for the dose per pulse dependence,and the response trends of them were consistent.TomoDose showed angular response dependence with a maximum difference of 2.53％ for the gantry angle of ±60°.For the field size dependence,the response difference between the TomoDose and ion chamber was increased with the decreasing field size when the Jaw was 5.0 cm,and the maximum deviation was 0.78％ when the field size was 5.0 cm×2.5 cm.TomoDose could detect the couch distance error of 0.5 mm,and determine the couch velocity deviation of＜ 0.6％.For the Profile stability testing:In the x direction,there was always γ＜1 at the underwater depth of 15 mm for all values of Jaw;when the underwater depth was not 15 mm,there was always γ＜ 1 in the main beam region (off-axis distance＜ 200 mm),whereas in the penumbra region (off-axis distance＞ 200 mm),the value of γ was larger and even with γ＞ l.In the y direction,all comparison results of Profile under three field width demonstrated that γ index was larger on the edge of beam,whereas γ＜1 was found in all cases.Conclusions TomoDose is suitable f or the quality control of Tomotherapy,which can accurately measure the couch velocity,precisely monitor the stability of beam Profile of Tomotherapy and complete the quality control process in a convenient and efficient manner.
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Objective To investigate the impact of injection current (IC), injection voltage (IV), and pulse forming network (PFN) on energy (depth ratio D20/D10) and profiles of helical tomotherapy, and to improve the quality control for the stability of beam characteristics.Methods The energy and profiles were measured by ion chamber and TomoDose at different values of IC, IV, and PFN, the relationship between the energy and various parameters was evaluated by Pearson correlation analysis, and the changes in profiles were evaluated by comparative analysis.Results The energy had no correlation with IV and PFN values (P>0.05), but had a strong correlation with IC value (P=0.007), which showed a downward trend with the increase in IC.For the profiles in the x direction:(1) in the main beam region (-200 to 200 mm), the shoulder area of the profiles increased regularly with the increase in IC.There were no significant changes for the profiles when the IV values ranged from 6.42 V to 6.54 V, and the shoulder area of the profiles reached the highest point with IV=6.60 V, then decreased with further increase in IV.The shoulder area of the profiles decreased regularly with the increase in PFN.(2) In the penumbral region (±200 mm outside), all the three parameters had no effect on the profiles.For the profiles in the y direction:(1) in the main beam region (-20 to 20 mm), the profiles showed an upward trend in the area with an off-axis distance less than 16 mm when IC values were 5.40 V and 5.46 V, and showed an upward trend in the area with an off-axis distance less than 16 mm.But on the whole, the shoulder area of the profiles increased with the increase in IC, and was not affected by IV and PFN.(2) In the penumbral region (±20 mm outside), the profiles decreased regularly with the increase in IV, and was not affected by IC and PFN.IC had the highest influence on the profiles in the main beam region, followed by PFN and IV.Only IV had impact on the profiles in the penumbral region.Conclusions When the energy needs to be adjusted, the IC value should be given a priority, and PFN should be taken as a supplementary factor.When the profile needs to be adjusted, the IC value should be given a priority, and IV should be used as an auxiliary factor in the main beam region.But in the penumbral region, adjustment of parameters is only related to the profiles in y direction, so the IV value should be adjusted.This study has a guiding role in the quality control of energy and profiles, which can reduce the blindness of quality control, thus saving the time.
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Objective To investigate the γ pass rate and contributing factors by summarizing the plan verification results of 260 volumetric modulated arc therapy (VMAT) plans.Methods From 2010 to 2012,two different detector arrays (MapCheck2,Sun,Nuclear,USA ; Delta4 ScandiDos,Swenden) were used for plan verification in 260 patients.The measured dose distributions were compared with the calculation results of treatment planning system using γ pass rate (Pγ ≤ 1 for 2％/2 mm,3％/3 mm and 5％/3 mm,threshold 10％).And the results were put under independent-samples t test.The impact of multi-leaf collimator (MLC) on the γ pass rate (3％/3 mm) was analyzed.Results The average γ pass rates of 2％/2 mm,3％/3 mm and 5％/3 mm of 260 VMAT plans were 91.7％,98.5％ and 99.7％,respectively.Among 260 VMAT plans,3 VMAT plans (1.2％ of the total) failed to meet the clinical acceptable pass rate and needed to be redesigned or re-optimized.The γ pass rate of 2％/2 mm was slightly different between two measurement devices (90.0％ vs 93.5％,P =0.000),while the γ pass rate of 3％/3 mm showed no significant difference between two measurement devices and two accelerators (98.5％ vs 98.5％,P =0.926 and 98.5％ vs 98.6％,P =0.670).The γ pass rate (3％/3 mm) of the treatment plan before MLC calibration was 61.1％,compared to 94.1％ after calibration.Conclusions Most dose verification results of treatment plans can meet the clinical requirement.Gantry rotation may influence the γ pass rate of VMAT dose verification under stricter pass rate standard (2％/2 mm).MLC calibration is essential for VMAT.
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Small animal models are extensively utilized in the study of biomedical sciences. Current animal experiments and analysis are largely restricted to in vitro measurements and need to sacrifice animals to perform tissue or molecular analysis. This prevents researchers from observing in vivo the natural evolution of the process under study. Imaging techniques can provide repeatedly in vivo anatomic and molecular information noninvasively. Small animal imaging systems have been developed to assess biological process in experimental animals and increasingly employed in the field of molecular imaging studies. This review outlines the current developments in nuclear medicine imaging instrumentations including fused multi-modality imaging systems for small animal imaging.
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Animals , Animal Experimentation , Biological Phenomena , Models, Animal , Molecular Imaging , Nuclear Medicine , Tomography, Emission-Computed, Single-PhotonABSTRACT
PURPOSE: In order to obtain basic data for treatment plan in radiosurgery, we measured small fields of 6 MV X-rays and compared the measured data with our Monte Carlo simulations for the small fields. MATERIALS AND METHODS: The small fields of 1.0, 2.0 and 3.0 cm in diameter were used in this study. Percentage depth dose (PDD) and beam profiles of those fields were measured and calculated. A small semiconductor detector, water phantoms, and a remote control system were used for the measurement. Monte Carlo simulations were performed using the EGS4 code with the input data prepared for the energy distribution of 6 MV X-rays, beam divergence, circular fields and the geometry of the water phantoms. RESULTS: In the case of PDD values, the calculated values were lower than the measured values for all fields and depths, with the differences being 0.3 to 5.7% at the depths of 2.0 to 20.0 cm and 0.0 to 8.9% at the surface regions. As a result of the analysis of beam profiles for all field sizes at a depth of 10cm in water phantom, the measured 90% dose widths were in good agreement with the calculated values, however, the calculated penumbra radii were 0.1 cm shorter than measured values. CONCLUSION: The measured PDDs and beam profiles agreement with the Monte Carlo calculations approximately. However, it is different when it comes to calculations in the area of phantom surface and penumbra because the Monte Carlo calculations were performed under the simplified geometries. Therefore, we have to study how to include the actual geometries and more precise data for the field area in Monte Carlo calculations. The Monte Carlo calculations will be used as a useful tool for the very complicated conditions in measurement and verification.