Field Shape And Dose Verification Of Intensity Modulated Radiotherapy

Radiotherapy, surgery and chemotherapy are the three main techniques for tumor treatment. The development of three-dimensional conformal radiotherapy (3D-CRT), in which the high-dose volume matches the targets volume and avoids normal tissues, has been a major theme for improving the physical basis of radiotherapy, but it conforms only two dimensionally to the target projection in the plane perpendicular to the beam orientation.Intensity-modulated radiotherapy (IMRT) is the most advanced form of3D-CRT, it can produce highly three-dimensionally conformal dose distributions to the target. The clinical application of IMRT is a historic advancement for radiation therapy. The shape of hight iso-dose surface is agree with that of target in three dimension, and the dose gradient is steeper. It has accurate target dose, small dose of the adjacent normal organ, protecting critical organ and homogeneous dose distribution. However, the complexity of the treatment may increase the probability of errors in the treatment process. And the error will seriously affect the treatment effect, that means it may reduce the tumor control rate and increase the normal tissue complication. Therefore, the QA and QC of IMRT become the urgent problems to be solved and should be pay great attention to. Therefore, ensure intensity-modulated radiation therapy accuracy is extremely important. To insure the accuracy of intensity modulated radiotherapy, the Field shape and dose of radiotherapy was verified with special hardware and device. The location of the beam validation is refers to a special marker was used and assumed as verification target. And together with the patient CT scan, design plan will mark the ball set to position the target area to verify beam position verification. Beam shape validation is refers to the use of accelerator own beam video system (EPID) and treatment planning system (TPS) DRR figure by compared the beam shape verification. Absolute dose verification and relative dose verification are two aspects of dosimetric verification. Absolute dose verification is the way to check whether the dose at one point calculated by the quality assurance plan, which is produced by loading the IMRT treatment planning into the phantom, consists with the corresponding measurement. Relative dose verification is the way to check whether the referenced dose distribution on one plane calculated by the quality assurance plan consists with the corresponding measurements. For conventional therapy or conformal radiotherapy, we call check the dose of one or a few points to verify the plan and treatment delivery by manual. But for complex radiotherapy techniques, it is not sufficient because of the heterogeneous portal fluence and steep dose gradients. The film dosimeter, thermoluminescence gosimeter, gel dosimeter are effective tools for verification, but rather time-consuming and labor-consuming for use. As the advanced two-dimensional real-time dosimetric verification systems, MatriXX and EPID can obtain the two-dimensional data quickly. Finally, through the81cases intensity-modulated radiotherapy of nasopharyngeal carcinoma of the experiments, using the above three methods to verify the strong plan, timely correcting error, ensure accurate implementation plan.From the results of the validation position analysis, after adjusting the position, treatment bed X axis move to the right5.4mm, the bed Y axis up4.4mm, The Z axis in3.5mm. From the results of the validation beam analysis,81patients from81groups of verification, beam shape of validation error ratio than3results75%, error>3overall than the offset5%, the overall migration need to computing and adjust position. The results of the validation from dose analysis,81patients total of243set of authentication piece, dose validation quartile passing rate95%for186group,76.5%.95-90%of51group,21.0%.<90%for6group,2.5%. The six groups need to change the plan. The six groups need to change the plan. Mark ball of beam position validation, from the final link to avoid the position error of the system, achieves accurately illuminate. Use EPID system verify beam shape, can test electric grating leaves in place precision, ensure the dose distribution of TPS design in patients in the human body can achieve. Use of ionization chamber dose distribution matrix of verification, good agreement showed by visible IMRT plans the dose distribution of design and test results.In the last part of the paper, we also discuss some problems which haven’t been completed. In addition, some works which will be done in the future are prospected.