The Research For Dose Verification Of Imrt 6MV X Ray On Medical Electronic Linear Accelerator

Radiotherapy is using X rays,electron rays,proton rays,neutron rays and other heavy particle rays produced by radiographic devices such as medical accelerators,orβrays,γrays and neutron rays produced by isotopes such as⁹⁰Sr,⁶⁰Co,¹³⁷Cs,¹²⁵I,¹⁹²Ir and ²⁵²Cf.Medical electronic linear accelerator（LA）is one of the most commonly used medical accelerators.It can produce MeV electronic rays or MV X rays.From3D-CRT,it has gradually developed to S-IMRT,then developed to D-IMRT,and then to VMAT.IMRT is the main current form of radiotherapy,accounts for more than 50.0%of the radiotherapy.It mainly uses the MLC which can make the target area with high dose and the surrounding tissues or organs are irradiated very few,so as to achieve the therapeutic effect.IMRT has a complex radiotherapy plan,so the dose must be verified that the clinical dose and the radiotherapy dose for patients is same.The research was financed by Sichuan science and technology support program."Research on medical radiation hazard assessment and control technology（2012SZ0179）"and the key scientific research project of Sichuan provincial health and family planning commission."Study on the dose verification for X ray of IMRT（16PJ398）".First,QA and QC for mechanical positioning system,dose monitoring system and radiation field system of LA produced by ELEKTA were carried out.Second,the testing for clinical dose and factors for small fields were completed.Third,the verification for 2D and 3D clinical dose distribution were realized.Through above experiments,the factors that influence the performance and solutions were discussed,and getting a comprehensive verification method for dose system of medical linear accelerator.The main research contents,innovations and results are as follows:（1）QA and QC.The Iso-Align radiation field tester,PTW 3D scanning tank,Matrixx plate matrix ionization chamber,UNIDOS dosimeter and 0.60 cc finger ionization chamber were used to test the mechanical positioning system,dose monitoring system and radiation field system of the accelerator based on national standards.Then the testing and curve fitting for CF factors such asTPR²₁₀ ⁰and D20/D10of LA were measured accurately by Origin9.0.（2）The testing for clinical dose and factors for small fields.One dimensional scanning water tank,30.0 cm×30.0 cm×30.0 cm solid water model,dosimeter,finger ionization chamber and TLD were used to verify one dimension dose.Then,TPS and0.015 cc finger ionization chamber were used to measure the factors less than 5.0 cm×5.0 cm fields.The relative deviations among DTPS,DTLD and Dchamber were obtained,and the relative deviations of small fields output factors were only 0.53%¹.4%compared with the published value of international standards.（3）The 2D dose verification.15.0 cm×15.0 cm×15.0 cm teflon phantom was scanned by CT,and its images were transmited to TPS and made plan.The SSD was set to 90.0 cm,with the depth of 10.0 cm and radiation field of 5.0 cm×5.0 cm.The MUs were calculated at 6.0 Gy by 6 MV X ray.Finally,the center of the beams were aligned to the coordinate center,and the plans were implemented.Then,getting the relative deviation between DTLD and DTPS was 3.7%and the relative deviation between DFILM and DTPS was 1.5%.Finally,the 10.0 cm×10.0 cm and 5.0 cm×5.0 cm small fields,which were formed by the plate matrix ionization chamber and film,getting the results were 95.8%,96.2%and 97.1%and 97.3%.（4）The 3D dose verification.15.0 cm×15.0 cm×15.0 cm teflon phantom which contains PTV and OAR was scanned by CT,and its images were transmited to TPS and made plan by 6 MV X ray and export the whole plan.The SSD was set to 90.0 cm,with the depth of 10.0 cm and radiation field of 5.0 cm×5.0 cm.The phantom was irradiated 2 times,2.0 Gy each time,and the total dose of PTV was 4.0 Gy.The outlines and regions of PTV_ITLD,PTV_STLD,OAR_ITLD,OAR_STLD,PTV and OAR were sketched out by TPS,and calculates dose DTPS.Then the plan was used to verify the rate of 3.0 mm/3.0%through the plate matrix ionization chamber.Finally,the plan was transplanted to LA and irradiated,the dose DTLD and DFILM were obtained,the DICOMAN was used to 3D modeling,then getting the DVHs and dose DDVH.Finally,the relative deviations among DDVH,DTPS,DTLD and DFILM were calculated.