Choosing between the best, the easiest and the most usual: Three different dose prescription methods for HDR vaginal-cuff brachytherapy planning in postoperative endometrial cancer.

Purpose: To evaluate and compare dosimetry parameters of three planning methods in high-dose-rate vaginal cuff brachytherapy (VCB) using cylinders for postoperative endometrial cancer (PEC).

Material and methods: Two hundred seventeen patients were treated with 3D-based VCB for PEC, with the dose prescribed at 5 mm from the applicator surface. Three planning methods were retrospectively compared: T1-arm: point-based optimization at 5 mm from the applicator surface; T2-arm: volume-based optimization; T3-arm: graphical optimization. We evaluated the coverage index (CI), conformity index (COIN), D90 to clinical target volume (CTV) and dose to the organs at risk (OAR).

Statistics: Descriptive analysis, Chi-square test, Student`s t-test, GEE model, linear regression model.

Results: The mean CI was greater than 0.9 in all treatment arms. The T2-arm provided the highest COIN value while T1-arm provided the highest CI value. The T3-arm delivered the lowest doses to the vaginal CTV, rectum and bladder. The linear regression model suggested that in the T3-arm, COIN showed improvement at the expense of CI and achieving a balance between CI and COIN may be more feasible when administering the T2-arm.

Conclusion: The T2-arm may be considered a general optimization method since it provides a better COIN within an acceptable D90 to the CTV. However, the T3-arm is easier in daily practice and could be more beneficial for patients who are more likely to develop late complications in OAR. More studies are needed to clarify the correlation of late complications with planning methods and dosimetry variables.