Dose Verification Of Intensity Modulated Radiation Therapy

Objective: To discuss methods of the dosimetric verification for intensity modulated radiation therapy(IMRT), analyse affecting factor of dose verification, and insure accuracy of execution in the clinical IMRT practice. As a result a high efficient, virtual and low cost method of IMRT dose verification is provided for clinical objective.Methods: It includes three parts.(1) Ion chambert verification for absolute dose Choose 10 patient who will be treated as IMRT, design IMRT plan using Nucletron inverse three dimensional treatment planning system, and use solid flat water phantom of IBA as verifying phantom, and let patient plans of IMRT transplanted to the phantom, as a result a QA plan is created. One absolute dose point is choosed as a confirmed verifying point, according to QA plan requirement we make radiation on ELEKTA linac, then acquire absolute dose of verifying point which was measured using 0.65cc ion chamber. On the another hand three aspects were divided to research affecting factor for absolute dose verification, and analyze the result.(2) Film verification for relative dose Choose 10 patient who will be treated as IMRT, design IMRT plan using CMS Xio inverse three dimension treatment planning system, and use Cirs thorax phantom as verifying phantom, and let patient plans of IMRT transplanted to the phantom, as a result a QA plan is created, and one relative dose distribution plane is choosed to calculate for verification. According to QA plan requirement we make radiation on Primus linac, and acquire a dose plane film which was developed using self-develop film. We analyze actual measured and planned relative dose plane distribution by use of RIT113 film measurement software.(3) Plane dose distrubition measuring instrument verification for relative dose Choose 10 patient who will be treated as IMRT, design IMRT plan using Nucletron inverse three dimensional treatment planning system, and use solid flat water phantom of IBA plus mapcheck of Sunnuclear as verifying phantom, and let patient plans of IMRT transplanted to the phantom, calculate relative dose distrubition on detector layer, as a result a QA plan is created. According to QA plan requirement we make radiation on ELEKTA linac, we analyze actual measured and planned relative dose plane distribution by use of mapcheck plane dose measurement software. On the another hand three aspects were divided to research affecting factor for relative dose verification, and analyze the result.Results:(1) The ion chamber measured error absolute dose was between 3% for 8 patient, and 2 patient was between 5%, next three aspects will affect absolute dose verification results: accelerator geometry parameter, small dose MU linearity, accuracy of position .(2) 10 patient self develop film results all were very approximate on the high dose region and some different on the low region for the relative dose distribution.(3) 10 patient using mapcheck method the passing ratio was all above 90%, next three aspects will affect relative dose verification results: accelerator geometry parameter, small dose MU linearity, accuracy of position.Conclusion:(1) Through ten patients absolute dose verification, it proves that our research absolute dose verifying method is acceptable and virtual, it can be used as a absolute dose verification method for clinical IMRT.(2) Through ten patient relative verification with mapcheck, moreover it compares with film method, proves that our research method with mapcheck is a high efficient, virtual and low cost dose verification way for clinical IMRT .(3) As below three aspects affect absolute and relative dose verification of IMRT: accelerator geometry parameter, small dose MU linearity, accuracy of position .