Optimization And Improvement Of Precise Radiotherapy After Breast-conserving Surgery For Breast Carcinoma

PART 1 The exploration of the effect of free breathing movement during radiotherapy on the displacement of target volume and planning design after breast conserving surgery using special phase of four-dimensional CT(4DCT)Objective:To explore the effect of free breathing movement during radiotherapy on the displacement of target volume and planning design after breast conserving surgery using special phase of four-dimensional CT(4DCT).Methods:16 patients receiving radiotherapy after breast conserving surgery were chose,and 3DCT and 4DCT simulation images under free breath were obtained.Static intensity-modulated radiotherapy plannings including 3DCRT,IMRT and Hybrid IMRT were designed on 3DCT simulation images.Four respiratory phases(CTO%,CT25%,CT50%and CT75%)of the 4DCT,which were determined by the silver clip in the surgical cavity,were converted into the corresponding isocenter in the 3DCT image.A new treatment plan was made by reducing the original M.U.into 1/4 and copying it to four isocenters.Dosimetric differences of the target volume and organ at risk were compared between the new plan and the original plan.Results:The motion of the whole breast target area in the direction of the front and back,left and right,and head and foot were 1.44mm?0.74mm?1.97mm respectively in a calm breathing state.Vp,D2,D98 and Dmean were significantly reduced compared with conventional plan.However,the difference between HI and CI was not statistically significant.The Vp and Dmean of the BS plan in H_IMRT were significantly smaller than the conventional plan,while the difference of other parameters was not statistically significant.There is no statistically significant difference between all parameters of BS plan and regular plan in IMRT.V5,V20,V50 and Dmean of the affected lung,the maximum dose of the contralateral breast(D2)and the average dose of the heart were significantly higher in BS planning than in conventional plan.Conclusion:In the free breathing state,the displacement of the whole breast target area in the three-dimensional direction was small.This breathing movement reduced the target dose and prescription dose coverage of the CRT and H_IMRT plans,while increasing the exposure dose of the lung and heart.For the IMRT,respiratory movement had no significant effect on the dose distribution of the target area and the organs at risk.PART 2 Multileaf collimator shielding technique:reduce cardiac dose in hybrid intensity modulated radiotherapy after breast conserving surgery for left-sided breast cancerObject:To reduce the risk of radiation-induced cardiac injury in patients with left breast cancer after breast-conserving surgery by multileaf collimator(MLC)shielding technique.Methods:18 patients with left breast cancer after breast conserving surgery were selected to obtain 3DCT and 4DCT images at free breathing state.The target area was identified on the 3DCT image by registration with 4DCT images and to develop a hybrid intensity-modulated treatment plan(H_IMRT)and a Heart sparing hybrid intensity-modulated treatment plan(HSH_IMRT)to introduce MLC shielding technology to reduce the cardiac exposure dose,and to perform dosimetry verification of the treatment plan using the Compass verification system.The prescription dose was 50Gy in 25 fractions.Compare the dose parameters of the target area and the organs at risk in the plan results and the dose verification results,and match t test difference.Results:The results of the treatment plan showed that compared with H_IMRT,the dose uniformity of the target area of HSH_IMRT was better,and the difference of conformability was not statistically significant.The mean dose of the whole heart decreased by 23.67%(t=13.693,P=0.000)compared with the former.Dmax and Dmean of other substructures of the heart are lower than the former.The results of dose verification showed that there was no statistically significant difference in uniformity and conformity between the two planned target doses.The mean dose of the whole heart of HSH_IMRT was 24.88%(t=13.782,P=0.000)lower than that of H_IMRT,and except for the left ventricle and right ventricle,the Dmax of other heart substructures and Dmean of all heart substructures decreased.Both the planed and the dose verification results show that the V20 and the Dmean of the affected lung were lower in HSH_IMRT.Conclusion:Reasonable introduction of MLC shielding technology in H_IMRT can reduce the exposure dose of cardiac more while maintaining its dose characteristic advantage,and further reduce the risk of cardiac radiation damage.PART3 Application of modified fixed and dual laser lamp positioning system in the treatment delivery of precise radiotherapy after breast conserving surgeryOBJECTIVE:To investigate the application value of modified fixed and dual laser lamp positioning system in radiotherapy setup after breast-conserving surgery.MATERIALS AND METHODS:The purpose of this study was to simulate the height of the laser light of CT-SIM.A set of low-position laser lamps(90 cm from the ground)was installed under the isocenter laser lamp positioning system on both sides of the Synergy linear accelerator treatment room.Parallel to the isocenter laser light(124CM from the ground),the QA and requirements are synchronized with the linac laser system,once a week.Methods:A total of 36 patients were enrolled and divided into three groups:standard breast stent fixation(MED-TEC250)plus isocenter laser lamp setup group(group A);12 cases;standard breast bracket improved fixation plus central laser light setup group(group B);12 cases;standard breast bracket improved fixation plus low position laser light placement group(group C).12 cases;The setup error was verified by CBCT,and the verification was verified daily for the first five radiotherapy sessions,followed by weekly.The setup time is defined as the patient arrives at the treatment bed until the radiotherapist completes the setup and turns off the laser light.Compare the errors of the verification data and the difference of the setup time of A/B and B/C.RESULTS:1.Comparison of the setup error of the A/B group:108 scans in group A and 100 scans in group B,the position of CBCT scan in both groups can be seen:The linearity error:the up an/down and front/back directions of group B is better than the group A.2.Comparison of setup error between the B/C groups:102 scans in group B,105 scans in group C,the setup error of the two groups can be seen that the antero/posterior rotation error in group C is better than group B.Setup time:isocenter laser lamp placement group:76±7 seconds;low position laser lamp placement group:61 ±5 seconds.Conclusion:The dual laser lamp positioning system reduces the height of the setup during radiotherapy,which facilitates radiotherapist,ensures the positioning accuracy and saves the setup time.It is a recommended method in the radiation therapy treatment delivery.