Application of SWO technique in IMRT plan of post-operative cervical cancer / 中华放射医学与防护杂志

ABSTRACT

Objective To investigate the impact of segment weight optimization(SWO) technique on the intensity modulated radiation therapy(IMRT) plan for post-operative cervical cancer regarding the number of segments,monitor units (MU),the target homogeneity index (HI),conformal index (CI) and dose distribution of target volume and normal tissues.Methods Ten patients with stage Ⅰ and Ⅱ cervical cancer after radical resection were randomly selected for this study.The initial IMRT treatment plans were generated using ELEKTA XIO 4.62 system based on the step and shoot method (S-IMRT plan).With the same directions of fields and optimization parameters,the SWO tool was introduced to optimize the IMRT plans further (SWO-IMRT plan).Then the number of segments and MU were compared between the S-IMRT plan and SWO-IMRT plan.By using the dose-volume histogram (DVH),the target homogeneity index (HI),conformal index (CI) and dose distribution in the volumes of target and normal tissues were also analyzed.Results Compared with S-IMRT plan,the average number of segments in SWO-IMRT plan was decreased from 96 ± 4 to 87 ± 4 (t =10.049,P ＜ 0.05),and MU was increased from(638.79±35.02)) cGy to (672.03 ±39.07) cGy (t =3.5952,P ＜0.05).The maximum and mean doses of the planning target volume (PTV) decreased (t =2.262,2.323,P ＜ 0.05).A reduction of the maximum dose in the spinal cord was also observed [from (3856.00 ± 112.14) cGy to (3750.00 ± 141.38) cGy,t =3.976,P ＜ 0.05].The values of V30,V40,V50 in bladders,rectal V30 and L-femoral V50 were reduced in the SWO-IMRTplan (t=4.223,5.801,7.534,2.451,2.269,3.976,P ＜0.05).However,there was no significant difference in target homogeneity index(HI),conformal index (CI),rectal V40,V50,L-femoral V30,V40,V50,R-femoral V40 and V50.Conclusions The application of SWO technique in the IMRT planning for cervical post-operative cancer could reduce the total number of segments,doses in the spinal cord and bladder,but increase the total number of MU.As a result,the spinal cord and bladder toxicity can be reduced which enables an opportunity for dose escalation of gross tumor volume (GTV).SWO technique provides clinicians with an optional optimization solution in IMRT plan for post-operative cervical cancer patients.