| Objective: By comparing the difference between actual dose andplanning dose of targets and organs at risk for head and neck cancer patientstreated with helical TomoTherapy, to find out the feature of dose variation.Methods:12head and neck patients definitively treated with helicalTomoTherapy form August2012to December2012were included in thisstudy. All of the patients were confirmed by pathological diagnosis and havebody weight measured weekly. Patients were immobilized by mask andscanned under the CT simulator. The planning kVCT images were transferredto a Pinnacle9.2system, and contours for GTV, CTV1, CTV2, PTV andorgans at risk were drawn. The CT images and contours were sent to a helicalTomoTherapy planning system and the treatment plans were optimized then.After the plans passed the validation of Delta4system, the patients beganreceiving treatment. Prior to each treatment fraction, patients wereimmobilized on the treatment table using the same immobilization devices asduring the planning CT scan. An MVCT scan was performed in the treatmentregion. The MVCT images were automatically registered with the planningkVCT images before the manual registration was taken by the radiationtherapists, to correct the patients’ position. The kVCT images and the MVCTimages of the first day of each week since the second week during treatmentwere chosen, and dose distributions were recalculated on the MVCT images,which were the actual dose of each fraction. Each single dose distribution andthe corresponding CT image were sent to commercial software (MIM5.5), anddeformable image registration was performed to the CT images, and then thesum of actual dose was acquired by accumulating the single dose together. Thetargets and organs at risk were contoured on the MVCT images of the first day of the last week of treatment, according to the initial treatment plans. The plancontained the MVCT images of the first day of the last week of treatment, thetargets and organs at risk, and the sum of actual dose was called Plan2, theinitial plan was called Plan1. The dose distribution of targets and organs at riskof Plan1and Plan2were compared on DVH. Data analysis was performedusing an SPSS statistical package.Results:1Weight change during radiotherapy: All patients presented withdifferent degrees of decline in body weight after radiotherapy, from63.71±7.50kg before radiotherapy to58.98±6.42kg at the end of radiotherapy,or7.29%reduction in average.2Dose change of targets during radiotherapy: There were no significantdifferences between Plan1and plan2for D2, D50of GTV and D2of PTV.D95, D98, D100of GTV in Plan2is lower than in Plan1, and the percentagereduction was2.09%,2.74%,5.60%,(P=0.02, P=0.02, P=0.02) respectively.D50, D95, D98, D100of PTV in Plan2is lower than in Plan1, and thepercentage reduction was0.81%,1.9%,3.9%,13.5%,(P=0.02, P=0.02,P=0.02) respectively.3Dose change of organs at risk during radiotherapy: There were nosignificant difference between Plan1and plan2for dose distributions ofmandible and Body. Dose of spinal cord was higher in Plan2than in Plan1,increasing by an average of1.16%(P=0.04). Average dose and V26for doubleparotids were higher in Plan2than in Plan1, increasing by an average of37.74%,25.08%(P=0.00and P=0.00) for left parotid and30.45%,19.33%(P=0.00and P=0.01) for right parotid, respectively.4Homogeneity and conformity indices of PTV in Plan1and Plan2:Compared with Plan1, homogeneity and conformity indices of PTV in Plan2were significantly lower than in Plan1, and the percentage reduction was1.33%and3.52%, respectively (P=0.00, P=0.02).5Change of the volume of PTV: The volume of PTV significantlyreduced from795.44±173.39cm3in Plan1to762.26±152.55cm3in Plan2, and the percentage reduction was3.76%(P=0.009).6Change of the volume of parotids: The volume of parotids in Plan2wassignificantly lower than in Plan1, and the percentage reduction was29.06%and30.40%for left and right parotids, respectively (P=0.00and P=0.02).7Distance between the center of mass (COM) of parotids and the midlineof body: Distance between the COM of parotids and the midline of body wassignificantly smaller in Plan2than in Plan1, and the percentage reduction was6.72%and6.19%(both P=0.00) for left and right side, respectively.8The skin contour area in C2level: The skin contour area in C2levelwas significantly smaller in Plan2than in Plan1, and the percentage reductionwas5.0%(P=0.00).9Correlation analysis: There was no correlation between the percent ofreduction of weight and the percentage reduction of parotids’ volume, thepercentage increase of parotids’ V26, the percentage increase of parotids’mean dose, the percentage decrease of distance between the COM of parotidsand the midline of body. There was a linear correlation between the percentagedecrease of distance between the COM of parotids and the midline of bodyand the percentage increase of parotids’ V26, the percentage increase ofparotids’ mean dose. There was no correlation between the percentagereduction of parotids’ volume and dose to parotids in the initial plan, dose toparotids in Plan2. There was no correlation between the skin contour area inC2level and loss of weight, volume reduction of left parotids, decrease ofdistance between the COM of parotids and the midline of body, the doseincrease of parotids, but there is a linear correlation between the skin contourarea in C2level and volume reduction of left parotids.Conclusion: During radiotherapy for head and neck cancer patients,there was a difference between dose in initial plan and actual irradiation dose,owing to setup errors or weight change. D95, D98, D100of GTV and PTVwere found to be significantly decreased. Compared with Plan1, homogeneityand conformity indices of PTV in Plan2were significantly lower than in Plan1.Max dose of spinal cord and mean dose and V26of parotids were found to be significantly increased in Plan2. The shift of parotids to midline of bodyassociated with the dose increase of parotids. For patients who have asignificant anatomic change, in order to achieve the best therapeutic effect,modification of treatment plan at the appropriate time or applying of adaptiveradiotherapy is essential. |
PDF Full Text Request