The Study On The Planning Of Radiotherapy Quality Assurance

At present, the rate of cancer disease seems to be higher and higher, but the tumor can be effectively prevented from local recurrence by radiotherapy, surgery and Chemotherapy, and reduce the rate of distant metastasis. Among these methods, radiotherapy play more and more important role for the cancer treatment in clinical. With the fast development of computer technology and industry of machinery manufacturing, the function of linear Accelerator has continually been improved; the model of accelerators has been kept on upgrading. Meanwhile, the new technology of radiotherapy in recent years is also growing up,3D-CRT and IMRT have been widely utilized, combined with the technology of3D-CT image reconstruction, achieve at precise location、precise planning、precise Irradiation, however,3D-CRT can only fit on the shape of the tumor target, IMRT can make the distribution of dosage fit on the shape of target through modulating the intensity of X ray in a big field. Based on the development of3D-CRT technology, the execution time and Complexity of IMRT are largely increased, but the ultimate goal achieve at the "three precision" demand for the tumor radiotherapy.To achieve at the "three precision" demand of tumor radiotherapy, it is essential to do some of the radiation therapy quality assurance (QA). In general, we could divide the QA work into two facets:the examination of Mechanical precision and dosage precision. Examination of Mechanical precision is to verify and test the performance parameters, which include many Contents:precision of the iso-center location, the precision of Multi-leaf collimator, the precision of indication angle for component movement, the precision of indication calibration for the light ruler, the coincidence of location laser lights and the coincidence of light field and the treatment field. The examination of dosage is mainly to compare the dosage distribution result form the TPS calculation with the dosage distribution from measuring in reality by model, but we should test and verify the absorbed dosage for the reference point. The QA work of machinery precision should be prepared for dosage examination, it is necessary to make the machinery precision meet the required standards, so do this can we do the work of dosage examination. In this situation, dose Verification seems to be much important, which include many big fields and sub-fields, and different sub-field include different MU, so if we do not test and verify dosage distribution strictly, it is possible to generate high dosage error, which can lead to serious radiotherapy incident.The author of this article is working now in the First Affiliated Hospital of Guangzhou Medical College, which equipped with medical electron linear accelerator with Varian23EX and Siemens PRIMUS. The author firstly made an investigation about the actual situation of QA work from the first class hospitals, analyzing the advantages and disadvantages of various QA methods. Then, a series of QA programmers with the requirements of our hospital are developed considering the above advantages with a combination of our actual situation. Through the strict implementation of these programmers, we ultimately ensure the incidence of radiotherapy accidents to zero. The implementation tool of Intensity Modulated plan for dose Verification QA programmer is Mapcheck flat dose detector. The author first selected16patients’ Intensity Modulated plans, and the irradiation angle in each plan was divided into7beams. With the same target organ limit condition, direct machine parameter optimization (DMPO) and Intensity Modulated (IM) based optimization were used to generate different sub beam sequences. Then Mapcheck flat dose detector is utilized to respectively validate the pass rate of the above two optimizations. Results indicate that,16Intensity Modulated plans have the total16*7=112irradiation angles, and the pass rate of DMPO is higher than IM optimization in88irradiation angles, the DMPO and IM optimization having the same pass rate in2irradiation angles, and the pass rate of IM optimization is higher than DMPO in22irradiation angles.In the end, we summarized the ideas on how to design and carry out the QA program; meanwhile we look ahead the new QA program on new radiotherapy technology in future.