Dosimetric Study of Helical Tomotherapy in Patients with Cervical Cancer
Objective To evaluate the dosimetric advantage of helical tomotherapy technique in radiotherapy treatment planning for patients with cervical cancer.Methods 20 patients with cervical cancer were chosen randomly.After CT images were inputted into the Varian Eclipse13.5 treatment planning system,the same radiation therapy physician was invited to outline the tumor target volume.The prescribed dose was 50 Gy/25 fractions.Three seven-field IMRT plans(7F IMRT),volumetric mod-ulated are therapy(VMAT)plans and helical tomotherapy plans(TOMO)were designed for each patient.Under the premise that the 95%isodose curve covers the PTV,dose-volume histogram was applied to evaluate the PTV,conformal index(CI),heteroge-neity index(HI),maximum dose(Dmax),mean dose(Dmean),minimum dose(Dmin)and absorbed doses of organs at risk(OARs)in three plans.Results All plans of the three radiotherapy plan design methods meet the clinically prescribed dose limit require-ments for organs at risk.The heterogeneity index(HI)and conformity index(CI)of the target region in TOMO plan were signifi-cantly better than those of VMAT and IMRT plans,and the difference was statistically significant(P＜0.05).The TOMOplanwas significantly superior to the VMAT plan and IMRT plan in terms of the absorbed doses volume from V20 to V50 of bladder,the V30 and V40 of rectum,V30 and mean dose of bilateral femoral head,max dose of spinal cord,showing statistically significant difference(P＜0.05).However,the three plans showed no obvious differences in terms of the absorbed doses of the kidney and bowel,with-out statistical significance.Conclusion Compared with the IMRT and VMAT plan for patients with cervical cancer,TOMO tech-nology has significant dosimetric advantages.TOMO plans significantly decreased the radiation dose and radiation volume of OARs surrounding the target area(e.g.,bladder,rectum and spinal cord)while increasing the CI and HI of PTV dose greatly,thus enab-ling the decrease in the incidence rate of radiation negative reaction damage.
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