Purpose: In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in cervical cancer,area of segment fields was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT). Methods: 12 cases of cervical cancer were confirmed in pathology and treated with step and shoot IMRT. Dose of PTV was 50Gy/25fractions. Every patient was designed 9 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator. All plans were optimized with the direct machine parameter optimization(DMPO) algorithm using the same set of optimization objectives. Number of maximum segment field was defined at 80 and minimum MU in each segment was 5MU,and minimal segment area was 2*1cm2,2*2cm2,3*3cm2,4*4cm2,5*5cm2,6*6cm2,7*7cm2,8*8cm2and 9*9cm2,respectively.Coverage,homogeneity and conformity of PTV,sparing of OAR, MU and number of segment were compared. Results: In this group, mean volume of PTV was 916.8±228.7 cm3. Compared with the area of minimal segment field increased from 2*1cm2 to 9*9 cm2,the number of mean MU was decreased from 1405±170 to 490±47 and the number of segment field was reduced from 76±4 to 39±7 respectively(p<0.05). When the limit of minimal segment area was increased from 2*1cm2 to 7*7 cm2,dose distribution of PTV,OAR,CI,HI and V2 3 were not different (p>0.05),but when the minimal segment area was 8*8 cm2 and 9*9 cm2,they were changed compared with 7*7 cm2 and below(p<0.05). Conclusion: The minimal segment field of IMRT plan designed by Pinnacle 8.0m planning system in cervical carcinoma should be enlarge reasonably and minimal segment area of 7*7 cm2 was recommend.

Purpose: To investigate the variability of the global gamma index analysis for IMRT and VMAT plans in Rectal Carcinoma, assess the impact of criterion by 3mm/3% or 4mm/4% gamma index and DTA method. Methods: In ten patients, five‐field IMRT plans with fixed gantry positions were compared to two dual arcs VMAT plans, each of them was optimized with Oncentra4.3 planning system, and designed by experienced planners using appropriate similar optimization parameters and dose constraints with a number of iterations to meet the clinical acceptance criteria. Plans were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Measurements of the plan dose distribution were performed and analyzed with Delta4 detector array by 3mm/3% or 4mm/4% gamma index and DTA methods. Results: All plans passed in the dose verification, for gamma criterion, an average of 93.13% of the detector points passed the 3 mm/3% for VMAT plans while in IMRT verification it was 96% (p=0.017), the lowest pass‐rate were 90.2% for VMAT and 91.2% for IMRT; For 4 mm/4% gamma criterion, an average of 97.15% of the detector points passed of VMAT plans compared to 99.36% of IMRT plans (p=0.052), the lowest pass‐rate were 91.5% for VMAT and 97.8% for IMRT. For DTA criterion, an average of 88.35% of the detector points passed of VMAT plans compared to 93.53% of IMRT plans(p=0.002). Conclusion: For the gamma criterion, VMAT and IMRT techniques can both achieve good dose verification with Delta4 detector array. However for the DTA criterion, it showed significant difference. Different criterions resulted in different pass‐rate, further studies are needed to evaluate the methods to verify the dose distribution for VMAT/IMRT plans, so appropriate method can be chosen in clinic in the future.

Purpose: To compare and analyze the characteristics of static intensity‐modulated radiotherapy (IMRT) plans designed on Elekta and Varian Linac in different esophageal cancer(EC), exploring advantages and disadvantages of different vendor Linac, thus can be better serve for clinical. Methods: Twenty‐four patients with EC were selected, including 6 cases located in the cervical, upper, middle and the lower thorax, respectively. Two IMRT plans were generated with the Oncentra planning system: in Elekta and Varian Linac, prescription dose of 60Gy in 30 fractions to the PTV. We examined the dose‐volume histogram parameters of PTV and the organs at risk (OAR) such as lungs, spinal cord and heart, and additional Monitor units(MU), treatment time, Homogeneity index(HI), Conformity index(CI) and Gamma index comparisons were performed. Results: All plans resulted in abundant dose coverage of PTV for EC of different locations. The doses to PTV, HI and OAR in Elekta plans were not statistically different in comparison with Varian plans, with the following exceptions: in cervical, upper and lower thoracic EC the PTV's CI, and in middle thorax EC PTV's D2, D50, V105 and PTV‐average were better in Elekta plans than in Varian plans. In the cervical, upper and the middle thorax EC, treatment time were significantly decreased in Varian plans as against Elekta plans, while in the lower thoracic EC treatment time were no striking difference. MUs and gamma index were similar between the two Linac plans. Conclusion: For the the middle thorax EC Varian plans is better than Elekta plans, not only in treatment time but in the PTV dose; while for the lower thorax EC Elekta plans is the first choice for better CI; for the other part of the EC usually Elekta plans can increase the CI, while Varian plans can reduce treatment time, can be selected according to the actual situation of the patient treatment.

Purpose: quantification and modelling of the dosimetric impact of the treatment couch in Monaco Treatment Planning System. Methods: The attenuation characteristics of couchtop EP was evaluated for two different photon acceleration potentials (6MV and 10MV) for a field size of (10×10) cm2. Phantom positions in A‐B direction: on the left half, in the center and on the right half of the couch. Dose measurements of couch attenuation were performed at gantry angles from 180° to 122°, using a 0.125cc semiflex ionization chamber isocentrically placed in the center of a homogeneous cylindric sliced RW3 phantom. Each experimental setup was first measured on the LINAC and then reproduced in the TPS. By adjusting the relative‐to‐water electron density (ED) values of the couch, the measured attenuation was replicated. The simulated results were evaluated by comparing the measurements and simulations. Results: Without the couch model included the maximum difference between measured and calculated dose was 5.5% (5.1%) and 6.6% (6.1%) for 2 mm and 5 mm voxel size, when the phantom was positioned on the left (center). The couch model was included in the TPS with a uniform ED of 0.18 or a 2 component model with a fiber ED= 0.6 and foam core ED= 0.1. After including the treatment couch, the mean dose attenuation was reduced from 2.8% without couch included to (0.0, 0.8, −0.2, 0.6)%. The 4 different values represent the 1 and 2 components model and 2 and 5 mm voxel grid size. Conclusion: For a uniform relative‐to‐water couch electron density of 0.18 a good agreement between measured and calculated dose distributions was obtained for all different energies, voxel grid spacings and gantry angles. Therefore, we conclude that the Monaco couch model accurately describes the dose perturbations due to the presence of the patient couch and should therefore be used during treatment planning. This project is supported by Technology Foundation for Selected Overseas Chinese Scholar, Ministry of Hebei Personnel of China