| OBJECTIVE:To measure the setup errors in breast cancer after breast conserving surgery treated withsimultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT) usingkilo-voltage cone-beam CT (KV-CBCT), and to evaluate the impact of the setup errors onthe dose distributions in tumor target volume and the peripheral normal tissues．What’s more,based on the built FBCT-CBCT deformable registration method, we aimed to establish thedeformation errors on the dose distributions in tumor target volume and the peripheral normaltissues．Adaptive radiation therapy was developed to compensate for setup error and organmotion was necessary.METHODS:1. Thirteen patients with breast cancer after breast conserving surgery undergoing imageguided IMRT (IG-IMRT) were included in this study．The patients who received dailykV-CBCT before simultaneous integrated boost intensity-modulated radiation therapy hadrecorded shift values in the medial-lateral, superior-inferior, and anterior-posteriordimensions.364CBCT scans were acquired at28fractions during the entire course ofradiotherapy.1092setup errors of these patients were acquired before treatment． By shifting the isocenter, these setup errors were introduced in the treatment planning system and thecorresponding impact of the dose distribution in tumor target volume and peripheral organswere evaluated．2. Eight patients with breast cancer after breast conserving surgery treated withsimultaneous integrated boost intensity-modulated radiation therapy (SIB-IMRT) wereinclude. CBCT images of these patients were acquired before each treatment. Then usingFBCT-CBCT deformable registration method, FBCT and CBCT to obtain mCBCT (modifiedCBCT), then the initial plan were mapped to mCBCT get actual dose. These deformableerrors were imported into the treatment planning system and the corresponding impact of thedose distribution in tumor target volume and peripheral organs were evaluated．RESULTS:1. Total of364sets of CBCT images were analyzed for13breast cancer patients. Thetranslational deviations of medial-lateral, anterior-posterior, and superior-inferior directionswere （2.2±2.3）mm,（2.7±2.3）mm,（3.0±2.6）mm respectively and the absolute maximumwere16mm,13mm and14mm. Within5mm of which accounted for93.9％,71.4％,81.9％respectively． More than10mm of which accounted for1.6％,0.9％,4.2％respectively．However comparing with the standard plan without setup error, the setup errorsin the simulated plan reduced the dose of95％planning target volume (PTV) by3.40Gy and1.71Gy of whole breast and tumour bed respectively．The dose to PTV Dminand Dmeanwerealso reduced by5.62Gy,6.99Gy and1.53Gy,0.87Gy of whole breast and tumour bedrespectively．The correction of setup errors improved the conformity index (CI) and thehomogeneity index (HI) for PTV．Statistically significance was observed in the CI and HI(t=-2.02and-3.02,7.91and2.63respectively, P<0.05)．No statistical significant wasobserved in the mean dose of lungs, heart, and contralateral breast between the two plans (P＞0.05)．Statistical significant was observed in the volume of lung, heart, and contralateralbreast accept5Gy,10Gy,20Gy between the two plans (P<0.05)．2. Total of224sets of CBCT and mCBCT images were analyzed for8breast cancerpatients. Significant difference was observed in the dose of5％,95％,98％, and mean doseof planning target volume (PTV). The CI and HI for the standard plan were (0.88±0.03), (0.83±0.03) and (1.09±0.02),(1.19±0.02)．Statistically significance was observed in thesedifferences (t=-2.02,-2.02and-2.11,-2.11respectively, P<0.05)．No statistical significantwas observed in the maximun dose of planning target volume (PTV) between the two plans(P＞0.05)． Statistical significant was observed in the volume of lung, heart, andcontralateral breast accept5Gy,10Gy,20Gy,30Gy,40Gy,50Gy between the two plans(P<0.05)．CONCLUSIONS:Set up error and deformation error affect the accuracy of radiotherapy. The necessity ofcorrect set up error and deformable error based KV-CBCT in the process of radiotherapy... |
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