| Liver tumor is one of the most common malignant tumors in the world,radiotherapy can effectively improve the local control rate of liver malignant tumor,the precise target delineation and patients’daily anatomical changes are important factors affecting the safety and efficacy of radiotherapy.At present,CT image guided radiotherapy is an important means to achieve precision radiotherapy.However,CT images have low soft tissue contrast and poor visualization of abdominal tumor and normal tissue.Compared with CT images,magnetic resonance images have higher soft tissue contrast,clear display of liver tumors,and no ionizing radiation.Therefore,magnetic resonance images guided radiotherapy is an ideal way to treat liver cancer.In order to verify the feasibility of 4DMRI guided delineation of internal target of liver cancer,and to provide a reference for individual radiotherapy plan for different liver cancer patients with MRI-guided daily adaptive radiotherapy,patients diagnosed with liver cancer by pathological or imaging examination were selected for retrospective study,and the results are as follows:(1)The 4DCT and 4DMRI of 23 liver cancer patients were collected within the same day,and the data were injected into MIM software to delineate tumor target and organs at risk.The tumor and liver volume,tumor range of motion and image artifacts displayed by4DCT and 4DMRI images were statistically analyzed.The mean GTV volume based on4DMRI was 136.42±231.27 cm~3,which was 25.04 cm~3(15.5%)less than that of 4DCT(161.46±280.29 cm~3).The average volume of ITV determined by 4DMRI was 166.12±270.43 cm~3,which was 22.44 cm~3(11.9%)less than that determined by 4DCT(188.56±307.57 cm~3).Liver volume in 4DMRI increased by 4.0%,compared with 4DCT.The difference in tumor motion by 4DMRI based on the centroid was greater than that of 4DCT in the left/right,anterior/posterior,superior/inferior directions,and the average displacement differences were 2.6,2.8,and 6.9 mm,respectively.The severe artifacts in4DCT were 47.8%(11/23)greater than in 4DMRI 17.4%(4/23).The results show that,compared with 4DCT,T2-weighted and navigator-triggered 4DMRI produces fewer artifacts and larger motion differences in hepatic intrafraction tumors,which is a feasible technique for primary liver cancer treatment planning.(2)A retrospective analysis of 10 liver cancer patients undergoing radiotherapy was performed using the Monaco treatment planning system.The patient location CT images and daily magnetic resonance imaging anatomical information were delineated in the planning system,and the dose coverage of tumor target receiving prescription was controlled by adapt to position(ATP)and adapt to shape(ATS),respectively.In MRI-guided daily adaptive radiotherapy for liver cancer,ATS improved PTV coverage(V100%)for 67.6%(48/71)of the fractions compared to ATP.The ATP that did not meet clinical requirements occurred in large tumors and the target delineation was not using 4D technology.This suggests that ATS should be used for large tumors,while 4D technology should be used for target delineation when ATP is used.(3)A total of 71 MRI-guided daily adaptive radiotherapy plans were statistically analyzed to study the dose of ATP and ATS to organs at risk.The colon constraint was violated in 8.5%(6/71)of the ATP fractions,and these violations were resolved in ATS.All the plans violating the dose limit of organs at risk occurred in the radiotherapy plans with organs at risk close to the tumor.For liver,the mean dose was reduced 1.6Gy in ATS compared with ATP(P<0.05).And ATS decreased the maximum dose for spinal cord,stomach,duodenum,colon and small bowel by mean of 1.8Gy、1.1Gy、2.2Gy、3.4Gy and0.3Gy,respectively(P<0.05).The results show that,the ATS should be used for tumor locations with stricter dose requirements,and the liver tumors with smaller and far away from OAR can use ATP which with target delineation by 4D technology to shorten the treatment time. |
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