Custom Cervical Brachytherapy Applicator Compared to Commercial Applicators: A Treatment Planning Study.
Abstract
Purpose
We aim to compare cervical cancer brachytherapy treatment plans created using custom 3D-printed patient-specific cylindrical templates (PSCTs) to commercially available hybrid interstitial applicators (Geneva/Venezia, Elekta).
Methods
High-dose rate (HDR) brachytherapy plans from ten previously treated cervical patients were included in this comparison. Five had been treated using tandem and PSCTs. The remaining were treated with commercial tandem and ovoids (Geneva). Treatment plans for each applicator type (Geneva, Venezia, PSCT) were generated using the original CT images and contours. Applicator models (Oncentra, Elekta) were used to simulate the implant and generate commercial applicator plans. The model tandem was aligned to the implanted tandem. Ovoid size and PSCT diameter were selected to best match the implanted applicator dimension abutting the cervix. Interstitial needles were digitized along all Geneva and Venezia applicator channels. The PSCT needle positions/orientations were designed to cover the high-risk CTV (HRCTV) extent. All treatment plans targeted the HRCTV with a 28Gy/4 prescription dose. Standard 2Gy equivalent dose evaluation metrics combined HDR treatment with 45Gy/25 external beam radiotherapy. The median difference between commercial applicators and PSCTs plans was determined, reporting HRCTV D90% and organs-at-risk D2cc.
Results
All treatment plans achieved clinically acceptable HRCTV coverage, with most treatment plans meeting the organs-at-risk constraints. Relative to Geneva, the PSCT plans had lower bladder, rectum, and sigmoid D2cc (median difference -3.2Gy, -2.6Gy and -2.8Gy). When compared to Venezia, PSCT plans had lower bladder, rectum, and sigmoid D2cc (median difference -2.8Gy, -1.5Gy, and -1.5Gy). Organ-at-risk D2cc constraints were statistically significant, while all other parameters were equivalent. Reported values are cumulative differences over four brachytherapy fractions. PSCT plans made more efficient use of interstitial needles, activating 76% of available needles.
Conclusion
Custom 3D-printed PSCTs can be used to treat cervical cancers with clinically equivalent HRCTV D90%, reduced organs-at-risk D2cc, and improved interstitial needle placement.