Dosimetric Study On Needle Path Optimization And Applicator Improvement In 3D Brachytherapy For Cervical Cancer

Purpose:1.To compare the dosimetric differences between free-hand method and virtual optimized method for implanting needles in intracavitary and interstitial combined brachytherapy（IC/IS BT）of cervical cancer,and to explore the improvement space of the existing interstitial brahcytherapy plan.2.To explore the dosimetric differences between 3D printing individualized applicator and standard three-tube applicator in intracavitary brachytherapy,and to provide some guidance for the clinical treatment of cervical cancer and vaginal cancer.Methods:1.74 high-dose-rate cervical cancer IC/IS BT plans（short for Treatment-Plan）for 22 patients,had been already treated,were randomly chosen.For each treatment plan,Nucletron Oncentra 3D brachytherapy planning system was used to redesign virtual optimized insertion method IC/IS BT plan（short for Optimized-Plan）.Dose volume histogram was used to evaluate dose distribution in clinical target areas and exposure dose to organ at risk（OAR）.2.29 patients who received high-dose rate IC BT were divided into 16 patients in the standard three-tube applicator group and 13 patients in the 3D-printed individualized applicator group.Nucletron Oncentra 3D brachytherapy planning system was used to design 3D IC BT plan.Dose volume histogram was used to evaluate dose distribution in clinical target areas and exposure dose to OARs.Results:1.In the case where HR-CTV D₉₀ and IR-CTV D₉₀ were similar,compared with Treatment-Plan,Optimized-Plan’s D₁₀₀ and V₁₀₀increased by 20.07 cGy（P=0.002）and 0.36%（P=0.003）respectively,V₁₅₀（P=0.001）and V₂₀₀（P<0.001）decreased by 2.01%and 3.19%respectively.Optimized-Plan’s conformal index and dose homogeneity index of target dose distribution were superior to Treatment-Plan,and differences were statistically significant（P<0.001,P=0.001）.The differences of D0.01cc,D1cc,D2cc,and D5cc in bladder,rectum,sigmoid,and small bowel were all statistically significant（P<0.001）.Optimized-Plan could better reduce the dose of OAR than Treatment-Plan.2.In the case where the HR-CTV D₉₀ was approximated to 7Gy,there were no significant differences in D₁₀₀（P=0.907）,V₁₀₀（P=0.758）,V₁₅₀（P=0.399）and V₂₀₀（P=0.118）between the two groups.The IR-CTV D₉₀for the 3D-printed individualized applicator group and standard three-tube applicator group were（423.35±56.45）cGy and（393.48±36.31）cGy respectively,difference was significant（P=0.005）.The D0.01cc,D1cc,D2cc and D5cc of the bladder,sigmoid and small bowel of the 3D printing individualized applicator group were lower than the standard three-tube applicator group,but the D0.01cc,D1cc,D2cc and D5cc of the rectum increased.The differences were statistically significant（P<0.05）.Conclusions:1.Compared with the free-hand method,virtual optimized method had a dosimetric advantage,which could increase the dose of the target area,and the conformality and uniformity of the target dose distribution were better.At the same time,the doses of OARs were reduced to different degrees.These illustrated that there still have improvement space for the interstitial brahcytherapy plan.2.Compared with the standard three-tube applicator group,the 3D printing individualized applicator can achieve the prescription dose requirement in the target area,and the radiation doses in the bladder,sigmoid and small bowel are reduced,and the rectum exposure dose is increased,but within the range of dose limits.The individualized vaginal mold made by 3D printing technology is suitable for brachytherapy treatment of cervical cancer and vaginal cancer,and its clinical effect and adverse effects await further investigation.