ObjectiveTo study of the impact on dose distribution by electron width of energy spectrum and angular distribution using Monte Carlo simulation.MethodsThe simulated electron energy spectrum and angular distributions was as the input parameters and percentage depth dose (PDD) and offaxis curves were simulated by a modified PENELOPE code package. Results PDD and off-axis dose distribution curves are almost the same and are not sensitive to energy spectrum width and angular distribution with the exception of energy spectrum width of 2.5 MeV with obviously different curves.ConclusionsIn the situation of clinical treatment,spectrum and angular distributions can be ignored when their width are not very large.It is helpful to save about 9％ time by using monoenergy beams in treatment planning system development.

Objective To study the impacts of different applicators on dose distribution in 192 Ir brachytherapy. Methods The inner tubes of two cylinder applicators from Nucletron,#101?001 and#084?350, were made of plastic and stainless steel, respectively. The cylinder parts of them were made of plastic, and had four different radiuses:1?00 cm, 1?25 cm, 1?50 cm, and 1?75 cm. EGSnrc program was used to simulate dose distribution when applicators were present in a phantom, and the results calculated by the treatment planning system were compared with the results of EGSnrc. The impacts of applicators on dose distribution were analyzed with different materials, thickness, and numbers of resident source. Results There was no significant relationship between dose deviation and the radius for the two applicators. When an applicator was present, the actual dose delivered to a patient was smaller than the planned dose. The dose deviation of the applicator#101?001 was no more than 1%, while the dose deviation of the applicator#084?350 was close to 3%. The dose deviation remained the same when the number of resident source changed. Conclusions The plastic applicator, if possible, is the best choice for brachytherapy right now. In a long term, in order to promote the accuracy of brachytherapy, current dosimetry algorithm should be improved, and the impacts of the applicator made of metal, such as stainless steel, on dose distribution should be taken into account.

Objective To investigate the feasibility of the virtual source model in Monte Carlo dose calculation for clinical radiotherapy.Methods The Monte Carlo simulation was used to obtain the phase space files which recorded the physical properties of the particles emitted by a medical linear accelerator, and the information on the type, energy spectrum, and distribution of particles were extracted from these files and analyzed to establish the semi-empirical model of virtual two-photon source.The GMC dose calculation engine was used to obtain the 3 cm×3 cm, 5 cm×5 cm, 10 cm×10 cm, 20 cm×20 cm, and 30 cm×30 cm fields of radiotherapy and the results of Monte Carlo simulation of dose distribution in three-dimensional water phantom in 2 intensity-modulated radiotherapy ( IMRT) plans.These results were compared with the results of water phantom measurement or the results of Elekta Monaco planning system to verify the accuracy of Monte Carlo dose calculation based on a virtual source.Results As for the percentage depth-dose distribution curves of the central axis of the water phantom and the off-axis dose curves at different depths in the five fields for radiotherapy, the difference between the results of Monte Carlo simulation and the results of measurement was within 1%.As for the two IMRT plans, the three-dimensional passing rates of Monaco calculation results and Monte Carlo simulation results were 98.9%and 99.4%, respectively, for 3%/3 mm, and 95.1%and 95.4%, respectively, for 2%/2 mm.Conclusions Monte Carlo simulation based on the virtual source model can obtain accurate results of radiotherapy dose calculation.

Objective To investigate influence on dose distribution due to cavity and inhomogeneous structures using thermoluminescence dosimeters (TLD) and Chengdu phantoms.Methods A cavity 4 cm × 4 cm × 3 cm was made by a head and neck phantom and a lung phantom was cut into slices which were got a CT scanning and setup in a digital simulator.The TLD were pasted on edge and in the center of cavity structure and inhomogeneous structures.Treatment plans of different radiotherapy technologies were made generated and delivered on a linear accelerator.Then the TLD were read and analyzed.Results There were remarkable cavity effects of conventional single field,opposite fields and IMRT plans with 7 fields for head and neck phantom.There is similar effect in lung phantom.The more complexity the radiotherapy technology was the less cavity effect.Conclusions It is necessary to consider using more advanced radiotherapy technology or applying more fields to make treatment plans in order to decrease the cavity effect or similar effect when there are inhomogeneous structures.

Objective:To evaluate the application value of robost optimization of brachytherapy for cervical cancer.Methods:Twenty patients who completed radical treatment were recruited in this study. The dose volume histogram (DVH) parameters were statistically compared between the conventional and robust optimization plans, and the robustness between the conventional and robust optimization plans was evaluated using DVH and DVH bands. The robust optimization method utilized the worst dose distribution to consider the dose in the presence of uncertainties. In each optimization iteration, the dose distributin when the radioactive source shifted along the X, Y, and Z directions (±2 mm), and the dose distribution when the radioactive source was not shifted were calculated. The worst dose distribution for each voxel was the lowest dose in the target and the highest dose outside the target under all circumstances. The iterative objective function was calculated by the worst dose distribution.Results:In the scenario of no shifting of radioactive source position, the mean value of robust optimization was significantly lower and that of V 150% was significantly higher than those of conventional optimization (both P<0.05). When considering the shifting of radioactive source position, the worst dosimetric parameters of multiple dose distributions were statistically compared. The mean HR-CTV D 100% values did not significantly differ between the robust and conventional optimization plans, whereas the mean D 90% value (range: 0.02-0.03 Gy) of robust optimization was significantly higher than that of conventional optimization ( P<0.05). Robust optimization increased the D 2cm 3 of the bladder and small intestine, and the rectum dose was increased with the shifting of the radioactive source position in the robust optimization. The DVH bands did not significantly differ between the conventional and robust optimization plans for all patients. Conclusions:Robust optimization based on the worst dose distribution fails to significantly improve the robustness of brachytherapy for cervical cancer. Alternative methods are required to minimize the dosimetric effect of uncertainties in brachytherapy.

Objective To investigate the dosimetric influence of dwell weight standard deviation (DWSD) and applicator displacement in cervical cancer patients treated with three-dimensional brachytherapy.Methods A total of 20 cervical cancer patients who had completed radical treatment were selected in this study.The Fletcher applicator (Nucletron#189.730) was used for these patients.A new plan,based on the former CT images and structures,was designed for each patient.In former and new plans,dwell weight was recorded,and DWSD was calculated.Two groups,low-DWSD (LDWSD,0.141-0.299) and high-DWSD (HDWSD,0.211-0.337),were set according to the DWSD size for the two plans.Dosimetric effects from ± 1 mm displacement of tandem applicator or ovoid applicator were simulated with Oncentra (R) Brachy V4.3 treatment planning system.D100,D90,and V150 for clinical target volume (CTV)and D0.1cc,D1cc,and D2cc for the bladder,rectum,and sigmoid were evaluated.Dosimetric comparisons were made between the LDWSD group and HDWSD group to study the dosimetric effects of DWSD and applicator displacement in cervical cancer patients.Results The dosimetric effects from applicator displacement increased with increasing DWSD.If there was a 1 mm displacement of tandem applicator or ovoid applicator,D100,D90,and V150 of CTV were 3.0％,23.8％,and 4.8％ higher or 0.5％,1.2％,and 5.2％ higher in the HDWSD group than in the LDWSD group;D0.1cc,D1cc,and D2cc of the bladder and rectum were significantly higher in the HDWSD group than in the LDWSD group,particularly for the sigmoid (up 44.0％,22.8％,and 16.8％) and (up 10.3％,14.4％,and 12.4％).Conclusions DWSD should be considered in plan evaluation for cervical cancer patients treated with three-dimensional brachytherapy.The dosimetric influence from applicator displacement can be decreased by reducing DWSD properly.

Objective To explore the elementary properties of LiF (Mg,Cu,and P) thermoluminescent dosimeter (TLD) in dosimetry for tumor radiotherapy,and to provide a reliable basis for thermoluminescent dosimetry in clinical radiotherapy.Methods 60Coγ-ray and 6 MV X-ray were used for evaluation of the dispersion,repeatability,and dose response of LiF TLD.To meet the requirement of clinical radiotherapy,the effects of energy,dose (50-600 cGy),radiation dose rate (50-600 MU/min),and the angle of incidence for accelerator gantry (0°-± 90°) on TLD were determined and the respective correction factors were calculated.Results The errors of repeatability and dispersion of TLD were less than ±3％.There was a linear relationship between readout and irradiation dose within a certain range of irradiation dose.The minimal relative deviation of 0.3％ was obtained when 6 MV X-ray was used with a dose rate of 300 MU/min and an angle of incidence of 0°.Conclusions LiF TLD shows excellent repeatability,low dispersion,high stability,and strong linear correlation.It meets the international criteria and can be used for dose measurement in tumor radiotherapy.

Objective To study the impact of setup error caused by computed tomography ( CT) images with different resolutions in the Sentinel system on clinical treatment. Methods A phantom was scanned by large?aperture positioning CT with two different resolutions ( CT1:0. 5 mm × 0. 5 mm × 1. 0 mm, FOV 256 mm, Matrix 512, thickness 1 mm;CT3:1. 0 mm×1. 0 mm×3. 0 mm, FOV 500 mm, Matrix 512, thickness 3 mm) . The CT images were transferred to the planning system. The radiation fields were designed and transferred to MOSAIQ and Sentinel systems. Ten fixed setup errors were applied to a six degree of freedom couch. The Sentinel system was used to position the two groups of CT images and generate the setup errors. The comparison of two datasets was made by paired t?test. Cone?beam CT was used for independent verification. Results The setup errors in x?, y?, and z?directions were significantly smaller on CT1 than on CT3(0.19±0. 11 vs. 0.33±0. 16 mm, P=0. 061;0.59±0. 79 vs. 1.07±1. 09 mm, P=0. 008;0.67±0. 75 vs. 1.16±1. 30 mm, P=0. 043). There were no significant differences in rotational errors in x?, y?, or z?directions between the two datasets ( P=0. 494;P=0. 182;P=0. 298) . Conclusions The Sentinel system has a higher setup accuracy in the 0. 5 mm×0. 5 mm×1. 0 mm mode than in the 1. 0 mm×1. 0 mm×3. 0 mm mode. However, the later mode is still an acceptable choice in clinical treatment.

Objective To understand the status of the radiation therapy in sichuan province, analysis the development level of radiotherapy in the past five years in sichuan province,provide reference for the rational allocation of radiotherapy resources in the province, promote the healthy development of radiotherapy. Methods With reference to the surveys carried out by other provinces and the survey of sichuan province in 2009,to determine the survey schemes,survey projects. The survey covers all medical units of radiation therapy in the province, adopt the way of combination of questionnaire and on?the?spot visiting. Results There is a big progress in basic condition, treatment equipment, auxiliary equipment, verification equipment,personnel and application of new technologies. Compared with 2009 survey,multiple projects achieve a 50% or even more than 100% growth. Conclusions The rapid development of radiation oncology in sichuan province will ultimately benefit a large number of tumor patients in sichuan province. Patients will be treated with better environment,treatment technology and quality. At the same time,higher requirement of quality control for the entire province is put forward to us.