Applied Research On Independent Checking Calculation And Measurement Verification Of Three-dimensional Dose In Intensity Modulated Radiotherapy

Intensity-modulated radiotherapy technology（IMRT）is complicated to implement and requires strict quality assurance methods and measures.Before the treatment plan is executed,it is necessary to check the dose calculation results of the treatment planning system through the independent dose calculation to ensure the accuracy of the dose calculation of the treatment planning system.The early independent calculation checked and calculated the number of hops in the treatment plans in general.Due to the lack of information on the three-dimensional dose distribution,it was impossible to compare the dose deviation of the targets and the organ at risks（OARs）.Therefore,independent three-dimensional dose calculations had been implemented in clinic.In the verification of dose measurement,current two-dimensional dose verification of the treatment plan cannot fully reflect the execution deviation of the linear accelerator,nor can it accurately reflect the relationship between the patient’s anatomy and the dose deviation.Therefore,the development of three-dimensional dose verification of intensity-modulated plans is a trend in the development of physical technology for radiotherapy quality assurance.In this article,the application research of 3D dose verification would be based on the Electronic Portal Imaging Device（EPID）and the detector matrix.IBA three-dimensional water tank was used to collect data according to the software requirements,then the data was imported into EDose and COMPASS for physical modeling.By adjusting the modeling parameters,the modeling results were in consistent with the measurement results.The modeling results showed that in the two verification systems,the reconstructed off-axis ratio curve of the field had good consistency with the measurement results of the three-position water tank in the flat area and the penumbra area,while the measured value in the low-dose area of the field was slightly higher.The percent depth dose curve（PDD）in the built-up area had a relatively large deviation between the reconstructed result and the three-dimensional water tank measurement result,but the difference after the built-up depth was small.After modeling,AAPM TG-119 recommended tests were carried out to test the physical modeling results.In this paper,two systems were used to study the independent three-dimensional dose calculations.The results showed that the DVHs of EDose independent calculation of nasopharyngeal carcinoma had little deviation,The Gamma pass rate（3%,3mm）of targets and OARs fluctuated around 97%,Gamma pass rate（2%,2mm）was 87%.The deviation of the DVHs by independent dose calculations of lung cancer was slightly larger.The Gamma pass rate（3%,3mm）of both lungs was93.67%,and the standard Gamma pass rate（2%,2mm）was 84.74%.The remaining targets and OARs,Gamma pass rate（3%,3mm）was about96%,Gamma pass rate（2%,2mm）was about 87%.The DVH results of COMPASS nasopharyngeal carcinoma independent calculation had little deviation.The Gamma pass rate（2%,2mm）of target area and OARs fluctuated around 96%,which was quite different from the Gamma pass rate of EDose（2%,2mm）.The independent calculation results of lung cancer were more similar to the independent calculation results of COMPASS.We retrospectively selected 20 cases of nasopharyngeal cancer and lung cancer in the First Affiliated Hospital of Guangxi University of Traditional Chinese Medicine from 2019 to 2020,and each plan adopted dynamic IMRT.Two three-dimensional dose verification systems were implemented for independent three-dimensional dose calculation and dose verification.DVH analysis,Gamma pass rate analysis and comparison were made between the reconstructed dose and the calculated results of the radiotherapy planning system.Differences between dose distribution of COMPASS dose reconstruction and TPS calculation were found for 20 cases of nasopharyngeal carcinoma,especially in the D_2%and D_98%of the targets.Differences was also found between the EDose three-dimensional dose reconstruction results and the TPS calculation results,and the overall target area deviation was around 1%.The deviation of the EDose calculation result in D_2%is smaller than that of the Compass calculation result,and D_98%is similar.EDose and Compass generated similar results under（5%,3mm）Gamma pass rate.All the pass rate of nasopharyngeal cancer Gamma was above 98%,and the pass rate of lung cancer Gamma was above 97%.The gamma pass rate of each plan under the standard of（3%,3mm）was not much different from that of（5%,3mm）.The Gamma pass rate（2%,2mm）of the Compass was far behind EDose.The Gamma pass rate of nasopharyngeal cancer was 90%-95%,and the pass rate of lung cancer was around 86%.The research results showed that the results of the EDose and COMPASS three-dimensional dose verification system were accurate and reliable,and could provide sufficient dose verification data for clinical three-dimensional plan verification.