Variation Of Organ Position And Dose For Cervical Cancer Patients Treated With Helical Tomotherapy

Objective: By observing interfractional tumor and organs variation,comparing the difference between actual dose and planning dose of targets andorgans at risk for cervical cancer patients treated with helical tomotherapy, tofind out the feature of variation, then guide clinical application.Methods: This study consisted of twelve cervical patients treated withhelical tomotherapy from August2013to February2014. Five patientsreceived radical radiotherapy while seven received adjuant radiotherapy afteroperation. Patients underwent CT simulation in the supine position withcustom immobilization. The planning kVCT images were sent to a Pinnacle9.2system, and contours for GTV, CTV, PTV and OARs were drawn. The CTimages and contours were sent to a helical tomotherapy planning system andthe treatment plans were optimized then. After the plans passed the validationof Delta4system, the patients began receiving treatment. Prior to eachtreatment fraction, patients were immobilized in the treatment position usingthe same immobilization devices as during the planning CT scan. An MVCTscan was performed in the treatment region. The MVCT images wereautomatically registered with the planning kVCT images before the manualregistration was taken by the radiation therapists, to correct the patients’position. The kVCT images and the MVCT images of the first and third day ofeach week since the start of treatment were chosen, and dose distributionswere recalculated on the MVCT images, which were the actual dose of eachfraction. Each single dose distribution and the corresponding CT image weretransferred to commercial software (MIM6.0), and targets and OARs werecontoured on MVCT images according to the same principles. Comparing thedifferences between the actual radiation and planning. Data analysis was performed using an SPSS statistical package.Results:1Variation of target volume and position1.1Magnitude of cervix regression and movementThe mean decline in cervix volume and the maximum diameter is68.90%(P=0.006)、26.91%(P=0.001). The median LR, AP, CC shifts were-1.43mm (range-6.21to3.92),-7.72mm (range-18.07to-0.13),0.02mm(range-10.63to3.03). Cervix movement in AP shifts was larger.1.2Uterus movementThe median LR, AP, CC shifts were-0.40mm (range-6.66to3.30),-1.24mm (range-14.18to12.44),-6.51mm (range-48.23to1.34). Uterusmovement was greatest in CC shifts, less along the AP shifts, and least in LRshifts.1.3CTV volume and movement1.3.1The CTV volume in the start and the end of treatment was776.55±138.87cm3and763.62±136.19cm3in five patients received radicalradiotherapy. There was no significant change between them. The median LR,AP, CC shifts were-0.43mm (range-4.18to3.50),-1.68mm (range-5.19to1.90),-0.22mm (range-5.00to3.62). CTV movement in AP shifts was larger..1.3.2The CTV volume in the start and the end of treatment was582.81±67.68cm3,576.17±77.88cm3in seven patients received adjuantradiotherapy after operation. The median LR, AP, CC shifts were-0.45mm(range-3.84to1.78),-0.81mm (range-5.18to2.04),-0.09mm (range-5.03to2.77). CTV movement in AP shifts of postoperative radiotherapy patients wassmaller than that in radical ones.2Dose changes of targets during radiotherapy2.1In the five patients received radical radiotherapy, all the GTV dose was≥95%of the prescribed dose in all interfractions. The CTV dose was＜95%of the prescribed dose in78%interfractions, the median V95%was99.40%,and the median missing volume was6.94cm3(0.00~32.30cm3). The uterus dosewas＜95%of the prescribed dose in46%interfractions, the median V95% was100%, and the median missing volume was0.00cm3(0.00~6.69cm3).2.2In the seven patients received postoperative radiotherapy, the CTV dosewas＜95%of the prescribed dose in52.94%interfractions, the median V95%was99.99%, and the median missing volume was0.06cm3(0.00~13.70cm3).The missing volume was smaller compared to the radical radiotherapypatients.3OARs volume and movement3.1Bladder volume and movement3.1.1In the five patients received radical radiotherapy, the bladder volumechanged from (149.77±111.22)cm3to (234.93±100.97)cm3. The median LR, AP,CC shifts were-1.37mm (range-13.15to1.50),2.39mm (range-6.38to13.78),-12.01mm (range-43.00to5.64). Badder movement was greatest inCC shifts, less along the AP shifts, and least in LR shifts.3.1.2In the seven patients received postoperative radiotherapy, the bladdervolume changed from (103.22±35.06)cm3to (298.82±205.39)cm3. The medianLR, AP, CC shifts were-1.48mm (range-8.64to5.57),4.66mm (range-5.72to14.57),-3.67mm (range-39.67to38.86). Badder movement was larger CCshifts.3.2Rectum volume and movement3.2.1In the five patients received radical radiotherapy, the rectum volumechanged from (42.55±3.58)cm3to (77.22±15.06)cm3. The median LR, AP, CCshifts were-2.25mm (range-6.43to3.49),-2.54mm (range-9.44to3.62),-1.05mm (range-9.42to8.73).3.2.2In the seven patients received postoperative radiotherapy, the rectumvolume changed from (65.00±19.72)cm3to (163.40±25.78)cm3. The medianLR, AP, CC shifts were-2.63mm (range-12.50to3.36),-1.26mm (range-7.41to5.58),-1.60mm (range-7.05to5.25).4Dose changes of OARs during radiotherapy4.1Dose changes of bladderThe radical and postoperative patients’ V45of bladder smaller than thatin the planning was34%fractions and99%fractions, respectively. The V45of bladder was≥50%in16%and7%fractions, respectively.4.2Dose changes of rectumThe radical and postoperative patients’ V45of rectum smaller than that inthe planning was68%fractions and81%fractions, respectively. The V45ofrectum was≥50%in54%and62%fractions, respectively.5Correlation analyses5.1Radical patients5.1.1In one of five patients, bladder volume and V45of the bladder hadsignificant positive correlation, one had significant negative correlation.5.1.2The percent of increase bladder volume has positive correlation with theposterior shift of GTV, negative correlation with the AP shift of uterus,positive correlation with the CC shift of uterus, negative correlation with theAP shift of CTV. There was positive correlation between the reduction ofbladder volume and the reduction of CTV V95%.5.1.3In three of five patients, rectum volume and V45of the rectum hadsignificant positive correlation.5.1.4There was positive correlation between the percent of increase rectumvolume and the anterior shift of GTV.5.2Postoperative patients5.2.1In one of five patients, bladder volume and V45of the bladder hadsignificant positive correlation, two had significant negative correlation.5.2.2The percent of increase bladder volume has positive correlation with theAP and CC shift of CTV. There was positive correlation between the reductionof bladder volume and the reduction of CTV V95%.5.2.3In five of seven patients, rectum volume and V45of the rectum hadsignificant positive correlation.5.2.4There was no correlation between the percent of increase rectum volumeand the shift of CTV, CTV V95%.Conclusion:1During radiotherapy for cervical cancer patients, the volume, position anddoses were different between initial plan and actual radiation. 2Based on IGRT, the expansions for CTV which were10mm AP,5mmradial margin had partial targets missing but limited. This kind of radiationwhether meet the need of clinicals should be tested by survival analysis.3The volume of bladder and rectum affects the doses of targets and OARs.Advising to void rectum, moderately fill bladder before treatment. Try tokeep the consistency of the volume degree of bladder and rectum betweeninterfractions.