Application Of Cone Beam CT Image Guidance In Breast Cancer Radiotherapy

Objective:Using cone beam CT(CBCT)image to measure the placement error of breast cancer patients,find an effective method to improve the accuracy of radiotherapy in postoperative radiotherapy,reduce the adverse effects of placement error on the target area and endangered organs,for breast cancer surgery Patient radiotherapy provides quality assurance.Methods:32 patients with breast cancer after breast-conserving surgery who underwent postoperative radiotherapy in our hospital were selected for breast position.The CT simulation simulator is used to perform chest positioning scan on the patient,and the clinician delineates the target area and the endangered organ according to the obtained CT positioning image information.The radiotherapy physicist reverse engineered the plan.After the doctor confirmed the plan,the former transmitted the plan to the linear accelerator,and the radiotherapy technician showed the open treatment position.Before radiotherapy,the patient's positional image was scanned by CBCT and compared with the localized CT image to obtain the placement error,and the on-line error correction was used to perform precise radiotherapy.The automatic gray scale registration method and the manual titanium clip registration method are used to calculate the position error data,and the difference between the two registration methods is compared.According to the CTV-PTV external formula Mptv(external release)= 2.5?+0.7? proposed by Van Herk,the range of expansion of each CTV to PTV(Mptv)is calculated.The treatment plan implemented for each breast cancer patient is assumed to be the standard plan(PlanSTD),which does not include the patient's placement error.Keep the standard plan parameters unchanged,and shift the center point of the standard plan to the X-axis,Y-axis,and Z-axis in the treatment planning system.The average value of the placement error obtained from the first three CBCT scans is the translation value.Expand the simulation plan(PlanSL),compare the standard plan and the simulation plan,and analyze the impact of the placement error on the target area and the dose distribution of the endangered organ.Result:1.After three consecutive alignment error corrections,the patient's placement error is reduced in the X-axis,Y-axis,and Z-axis directions before the correction,and the difference in the Z-axis orientation is most significant before and after the correction.Statistical significance(P <0.05).2.On the X-axis,Y-axis,and Z-axis,the placement error after automatic gray registration is(0.75±3.21)mm,(-1.02±2.58)mm,(-1.72±1.05)mm,manual titanium clip The placement error after registration is(0.55±2.55)mm,(-0.98±1.94)mm,(-1.16 ± 2.16)mm,and the placement error displayed by the manual titanium clamp registration method is smaller than the automatic grayscale registration mode display.The results of the placement error were statistically significant(P < 0.05).3.The automatic gray-scale registration method is Mptv in the X-axis,Y-axis,and Z-axis directions of 4.1mm,4.4mm,and 5.0mm respectively,and the manual titanium clip registration method is in the X-axis,Y-axis,and Z-axis directions.The results were 3.2 mm,3.8 mm,and 4.4 mm,respectively,and the correlation was statistically significant(P < 0.05).4.The positioning errors in the X-axis,Y-axis,and Z-axis directions displayed by the two registration methods are the largest in the Z-axis back side direction.5.Compared with the standard plan,the simulation plan after the treatment planning system simulated the placement error was poor in the 95% dose package of the PTV target area,and the comparison was statistically significant(P<0.05).6.The simulated V5,V10,and V20 values of the lungs were higher than the standard plan,and the difference was statistically significant(P<0.05).It can be seen that the corrected placement error can reduce the dose of the patient's affected lung.Conclusion:Using Using CBCT images to measure and correct the placement error of breast cancer patients in postoperative radiotherapy can help patients obtain more accurate radiation therapy.For patients with titanium clips after breast cancer surgery,manual titanium clip registration can effectively reduce the placement error and improve the accuracy of patient radiotherapy.The Z-axis,Y-axis,and Z-axis are most prominent in the Z-axis,which is related to the patient's respiratory motion.Compared with the standard plan,the simulated plan has a poor 95% dose package in the PTV target area.The simulated V5,V10,and V20 values of the lungs are higher than the standard plan.It can be seen that the CBCT image guides the correction of the placement error better.Protect the affected side of the lungs.