Utrecht Interstitial Applicator Shifts and DVH Parameter Changes in 3D CT-based HDR Brachytherapy of Cervical Cancer

Background: For brachytherapy of cervical cancer, applicator shifts can not be avoided. The presentinvestigation concerned Utrecht interstitial applicator shifts and their effects on organ movement and DVHparameters during 3D CT-based HDR brachytherapy of cervical cancer. Materials and
Methods: After theapplicator being implanted, CT imaging was achieved for oncologist contouring CTVhr, CTVir, and OAR,including bladder, rectum, sigmoid colon and small intestines. After the treatment, CT imaging was repeated todetermine applicator shifts and OARs movements. Two CT images were matched by pelvic structures. In bothimaging results, we defined the tandem by the tip and the base as the marker point, and evaluated applicatorshift, including X, Y and Z. Based on the repeated CT imaging, oncologist contoured the target volume andOARs again. We combined the treatment plan with the repeated CT imaging and evaluated the change rangefor the doses of CTVhr D90, D2cc of OARs.
Results: The average applicator shift was -0.16 mm to 0.10 mm forX, 1.49 mm to 2.14 mm for Y, and 1.9 mm to 2.3 mm for Z. The change of average physical doses and EQD2values in Gyα/β range for CTVhr D90 decreased by 2.55 % and 3.5 %, bladder D2cc decreased by 5.94 % and8.77 %, rectum D2cc decreased by 2.94 % and 4 %, sigmoid colon D2cc decreased by 3.38 % and 3.72 %, andsmall intestines D2cc increased by 3.72 % and 10.94 %.
Conclusions: Applicator shifts and DVH parameterchanges induced the total dose inaccurately and could not be ignored. The doses of target volume and OARsvaried inevitably.