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 study the dosimetry for copper compensator in IMRT.Methods 10 patients (3 nasopharyngeal carcinoma,4 esophageal cancer,3 colorectal cancer) from IMRT plans made in Oncentra Planning System enrolled in this study.The fluence matrices of each plan were converted into compensator thickness matrices based on attenuation coefficient of copper under 6 MV radiation ray which was measured with ion chamber.While irradiating the homogenous phantom with the intensity modulated plans performed by copper compensator,film was used to measure the planar dose.In the end,γanalysis was carried out between the measured and calculated planar doses with the criteria of 3％ DD/3 mm DTA.Paired t test to MU differences of MLC plans and copper compensator plans.Results The γanalysis results showed the planar dose pass rates of 10 plans lie between 90.2％ and 98.2％,which means the IMRf technique based on copper compensator can meet the clinical needs.The MU for copper compensator IMRT plans is less than the MLC IMRT plans (873.9 vs.975.1,P =0.005).Conclusions Compared to conventional IMRT based on MLC,copper compensator has the advantage of lower requirement of hardware and lower scattering dose in patient.Copper compensator can meet the needs of clinical practice.

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 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.

Objective To investigate the dose and mechanical properties of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province,China via sampling and inspection.Methods A total of eight radiotherapy units in Sichuan Province were selected by sampling,and the tests were performed for the dose and mechanical properties of the medical electron linear accelerators in use.Among these accelerators,there were 5 imported accelerators and 3 domestic accelerators.The test items and methods were determined according to the requirements in GB15213-94.Results Among the 14 test items,the items related to the flatness,symmetry,and overlap of radiation field.The other tests of dose accuracy and mechanical precision achieved good results.Conclusions There is a need to strengthen the daily quality control work for dose and mechanical accuracy of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province and perfect the allocation of professional equipment and personnel and training of related personnel.With the support of Sichuan Radiotherapy Quality Control Center,quality control supervision and guidance should cover the whole province.