Personalized 3D-Printed Cervical HDR Applicators: Algorithm-Guided Needle Optimization for Outpatient Brachytherapy
Abstract
Purpose
Develop an algorithm to personalize 3D-printed tandem&ovoid intracavitary/interstitial (hybrid) cervical HDR applicators to optimize needle placement while maintaining or improving target coverage.
Methods
HR-CTV volumes and points defining the central channel direction and left-right orientation were exported as DICOM and processed in MATLAB. A fixed ellipsoidal conical applicator with N peripheral needle channels – excluding direct anterior/posterior directions – was used as a proof of concept. Needle configurations were optimized iteratively, beginning with all straight needles. For each configuration, target points were assigned to the nearest needle, prioritizing the central channel. Two adaptive actions were alternated: (a) removing needles with assigned point sets below 3% of total or with narrow spatial support, and (b) rotating a stochastically selected needle with probability weighted by the largest target-to-needle distance. Iterations continued until all needles were removed or all angular permutations tested. The final configuration was imported into Oncentra for planning. The algorithm was retrospectively applied to structure sets from two hybrid and two interstitial perineal implants. Generated structures were used for simulated channel reconstruction. Prescription doses were 7Gy for hybrid and 5.5Gy for perineal implants. Plans were reviewed and compared against standard-of-care plans for HR-CTV (D90%,V100%) and OARs (D2cm³).
Results
Plans using personalized hybrid applicators achieved HR-CTV D90% within 0.1Gy of, and V100% up to 4% higher than standard plans, while OAR D2cm³ values were slightly increased but remained below EMBRACE-recommended cumulative EQD2 limits including 50Gy EBRT. Personalized hybrid implants required substantially fewer catheters for interstitial treatments: 6 vs. 21 and 10 vs. 25 (personalized vs. actual implant). To replace hybrid applicators with three needles each, the personalized applicators required 5–9 needles.
Conclusion
Personalized 3D-printed cervical HDR applicators with optimized needle placement can maintain dosimetric quality with fewer catheters and could facilitate outpatient interstitial HDR brachytherapy in lieu of inpatient treatments.