ABSTRACT
Objective To investigate the virtual wedge (VW) dosimetric parameters with the ionization chamber array Matrixxenvlution.Methods Using Matrixxenvlution and solid water to measure and calculate Siemens accelerator's VW angle and VW factors of different fields and compare the wedge field dose distribution to that of treatment planning system (TPS) by gamma analysis,summarized the measurement results of 50 times.Results The γ pass rate (3 mm/ 3％) of 15° and 30° VW in both direction were (91.47 ± 1.76)％,(92.99 ± 1.54)％ and (93.27 ± 1.24)％,(93.27 ± 1.68)％,respectively,with the increase of filed size and the VW angle,but for 20 cm ×20 cm field and VW 60°,the result was not very good.The largest angle deviation ＜ 2° except small field size and wedge angle,VW factors were approximately equal to 1,the maximum deviation was no more than 0.05,plan dose distribution and the measured dose distribution have good consistency except large field with large wedge angle.Conclusions Matrixxenvlution used in the measurement of VW dosimetric parameters which can obtain all parameters for angle calculation and dose plane analysis with only once positioning,and become more rapid,convenient,economical and practical one of quality assurance tools for VW dose verification.
ABSTRACT
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.
ABSTRACT
Objective:To inspect the dosimetry characteristic of a 2-D ionization chamber array and its response to oblique incident electron beam.And to discuss feasibility to using it to validate the electron arc therapy plan.Materials and methods:(1)The 2-D ionization chamber array was calibrated referring to a themble chamber,comparing the response to electron beams with incidence angle ranged from-50°to 50°.(2)Phantom test plans of 6 and 10MeV electron beam arc therapy were designed,with the beam rotation arcs of 30°,60°and 90° respectively,symmetric to the Central axis of 0°gantry angle.Dose distribution of each plan was verifled with the 2-D array.Results:(1)Measurement differences between the central detector of the array and the thimble chamber were less than 2%,under the planned oblique inddent 6/10MeV electron beam.(2)For the all test plans,dose error was less than 3%at dmax in the symmetric axis of the electron beam arcs.Off-axis dose error was less than 2%within the central 70%area of the profile in non-rotating direction,and smaller than 1.5%in the rotational direction.The measured dose distribution had good agreement with the TPS calculation in isodose curves between 100%and 20%.The gammapass rates(△D=5%,△d=5cm)were 99.98%、99.89%、99.74%、98.64%、99.16%and 99.44%respectively for 6 and 10 MeV plans with electron beam arcs of 30°,60°and 90°.Conclusion:it is practicable using the tested 2-D ionization chamber array to verify and validate the electron beam arc therapy plan.