ABSTRACT
Objective To investigate the effect of respiratory movement of different amplitude,period and direction on the dose distribution of target area in dynamic intensity modulated radiation therapy.Methods A total of 30 cases of lung cancer were selected and divided into three groups according to the volume size of the target area,including groups A (72.0-200.2 cm3),B (271.7-380.0 cm3) and C (498.9-684.9 cm3).The average volume was 151.5,327.1 and 583.3 cm3,respectively.Breathing motion simulation platform was used to drive the mode body with two-dimensional ionization chamber matrix along the Gun-Target direction,then turn the collimator to 0° and 90°,respectively.The doses were collected at the central level in different amplitudes of 0,4,8,12 and 15 mm,periodic respiratory movement at the intervals of 3,4 and 5 s and respiratory motion measurement with a cycle of 4 s 5 times.The difference of dose distribution between the collected dose and TPS output was analyzed by taking the absolute dose and γ-passing rate (3 mm/3％) as indicators.Results In the two-sided upward,respiratory movement reduced the dose at the medial edge of the target area and increased the dose at the lateral edge of the target area.The difference of γ-passing rate between respiration cycle was up to 3.54％ (t=2.301,P＜0.05),and when the respiration movement was more than 8 mm,the γ-passing rate was less than 90％ and decreased with the increase of amplitude.The difference of γ-passing rate between static and respiratory motion was negatively correlated with the volume of target area,and the average γ-passing rate of A,B and C three groups increased gradually.The γ-passing rate of 5 composited dose was higher than that of single dose,and the difference was statistically sigificant(t=-9.36--5.95,P＜0.05).Conclusions The dose distribution of dynamic IMRT target area is mainly influenced by respiration range and its own volume,and the respiration cycle has an effect on dose distribution under partial amplitude.After implementing the multiple doses,some single dose implementation errors can be eliminated.Physicians need to expand the target area reasonably according to the range of respiratory movement,and optimize the amount of marginal tissue in the target area in the direction of respiratory movement.For patients with small target volume and large respiratory movement,respiratory management technology should be adopted to improve the accuracy of target dose implementation.
ABSTRACT
Objective To investigate the feasibility of detector array in Monaco modeling for MLC parameters adjustment.Methods One parameter was fixed, and then the other parameter was changed.The γ pass rates of the test beams, namely 3ABUT, 7SegA, and FOUR L, were assessed to determine the values of leaf transmission and leaf offset.A total of 12 tumor cases from different anatomical sites were randomly selected.Two-dimensional dose verification (rack angle zero) of Step& Shot and dMLC plans as well as three-dimensional dose validation of VMAT plan were performed using Octavius 4D system.The γ pass rates were analyzed at a standard of 3%/3 mm.Meanwhile, the point dose verification for these three plans was analyzed to obtain the dose deviations.Results The values of leaf transmission and leaf offset were 0.0105 and-0.08 mm, respectively.The average γ pass rates (%) of Step& Shot, dMLC, and VMAT plans were 88.59±2.94, 87.81±3.28, and 87.45±2.24 before adjustment and 98.45±1.23, 98.9±1.01, and 96.03±1.66 after adjustment.In addition, the average dose deviations (%) according to the point dose verification were 0.85±0.75, 0.95±0.39, and 0.98±0.40 before adjustment and 0.97±0.57, 1.08±0.76, and 0.86±0.45 after adjustment.Conclusions Octavius detector 729 ionization chamber array is a feasible and reliable device in Monaco modeling for MLC parameters adjustment.
ABSTRACT
Objective To investigate the gamma (γ) passing rates for volumetric-modulated arc therapy (VMAT) dosimetric verification with different techniques.Methods A total of 12 VMAT plans for the treatment of different anatomical sites in cancer patients were chosen.The Octavius 4D system was used to measure the dose distributions in two different settings:the gantry was rotating (three-dimensional (3D) and 2D γ-analysis) and the gantry was fixed at 0°(2D γ-analysis).The γ passing rates were analyzed with 3%/3 mm and 2%/2 mm criteria, using the paired t test or Wilcoxon signed-rank test.The 2D γ passing rates for different irradiation methods were calculated.Results For the 3D and 2D dose distributions obtained at a rotating gantry angle as well as the 2D dose distribution obtained at zero gantry angle, the average γ passing rates were 96.03%, 96.98%, and 98.90% for 3%/3 mm (P=0.227, P=0.000, P=0.003);82.08%, 84.04%, and 90.90% for 2%/2 mm (P=0.379, P=0.000, P=0.000).For the 2D dose distributions obtained with different irradiation methods, the average γ passing rate was 98.99% for 3%/3 mm and 93.68% for 2%/2 mm.Conclusions The VMAT dosimetric verification based on a 3D volumetric dosimeter at a rotating gantry position can be clinically useful for delivery quality assurance (QA), and can achieve the most reliable dose calculation for VMAT, which has more referential values.
ABSTRACT
Objective To evaluate the effects of respiratory on dose distributions in threedimensional conformal radiotherapy (3 DCRT) and intensity-modulated radiotherapy (IMRT).Methods The dose distributions were measured with a PTW 2D-ARRAY seven29 placed on a home-made moving platform to simulate the respirator.Dosimetric comparisions for 3DCRT and IMRT plans were performed by means of Gamma analysis with 3％ and 3 mm,respectively.Dose distribution measured for static treatment plans.Results The respiratory could reduce the target does and conformal index.The r pass rate (3％3 mm in 3 DCRT was greater than it in IMRT ((53.58 ± 0.74) ％,(30.71 ± 1.00) ％,t =57.91,P ＜ 0.01).The failed points were mainly near the field edge,but located in the whole target volumes for IMRT plans.Conclusions It is undesirable to use IMRT techniques for tumors with large motion amplitude.3DCRT can give a reliable dose distribution by reasonably selecting the PTV margin.