| Background: Abdominal tumor is a common tumor disease among tumor diseases.In the treatment of patients with abdominal tumors,it was found that the intestinal tract of some patients caused a large area of the cavity in the intestine due to flatulence.If not treated,it will cause a large difference between the radiation dose and the actual.If the target area of the patient with flatulence is delineated and then the radiotherapy plan is designed,it will cause the value of the target area to be different from the actual dose received by the patient,and it will also cause a difference in the amount of organ-endangered,which will lead to the dose.The assessment was inaccurate.If the CT cavity area of intestinal patients is set to 1 in the planning system,the quality of the plan will be improved,and the radiotherapy for large-intestinal cavity patients will have potential.Purpose: To investigate the influence of intestinal air cavity and its volume change on the radiation dose of retroperitoneal lymphatic drainage area.Methods: The first planning computed tomography(CT)scan of patients was named CT1,and the air cavity was named air1.After 5-8 fractions of radiotherapy,a second CT scan was performed and named CT2,and the air cavity was named air2.In the conventional plan design mode,radiotherapy plan A was developed in CT1.After assigning the relative electron density of the air cavity as 1,only the dose calculation was revised for plan A;this was recorded as plan A1.Plan A was applied to CT2 to directly calculate the dose to obtain plan A2.In the improved plan design mode,the relative electron density of the air cavity was assigned as 1 in CT1 and plan B was generated by reoptimization.The dose recalculation was carried out for plan B to obtain plan B1 when the relative electron density of air1 had no value assignment.The Plan B was applied to CT2 to calculate the dose,obtaining plan B2.A dose analysis was performed to compare the following volumetric modulated arc therapy(VMAT)plans: plan A was compared with plan A1 and plan A2,and plan B was compared with plan B1 and plan B2.The above plans are all VMAT plans.When using the Monaco treatment planning system to design a full arc VMAT plan,the calculation grid is 0.3cm,6MV X-rays are used,the maximum control point is 200,and the calculation uncertainty is 1%.With a minimum subfield width of 1.0 cm.Results: When plan A1 was compared with the initial plan A,the dose indices of the target region,such as V50,Dmean,D98,D10,D5,and D2(P = 0.005 a,P = 0.000,P = 0.000,P = 0.003,P = 0.005,and P = 0.006,respectively)showed a significant decrease.For organs at risk(OARs),the Dmean of the right and left kidneys and the V30 and V40 of the small intestine were slightly increased,and the Dmax of the spinal cord was decreased.When plan A2 was compared with plan A,the V50 and D98 of the target region were decreased,while Dmean,D10,D5 and D2 were increased.The left kidney Dmean was decreased,while the right kidney Dmean,spinal cord Dmax,and small intestine V30 and V40 were increased.When plan B1 was compared with plan B,the doses of V50,Dmean,D98,D10,D5 and D2 in the target region were increased.For the OARs,the left kidney Dmean was decreased,while the right kidney Dmean,spinal cord Dmax,and small intestine V30 and V40 were increased,but all of these values met the dose requirements specified in the clinical requirements.When plan B2 was compared with plan B,the dose of D98 in the target region was decreased,while the doses of Dmean,D10,D5 and D2 were increased.For OARs,the Dmean of the left kidney was decreased,and the other dose indices were increased,but they still met the clinically specified values.Conclusion: For patients with Abdominal tumors with intestinal air cavity,it is feasible to optimally design the radiotherapy plan by assigning value to the relative electron density of the air cavity,which can further guarantee the radiation dose in the target region and decrease recurrence rate of tumor. |
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