Development and assessment of 3D-printed individual applicators in gynecological MRI-guided brachytherapy

Purpose: To evaluate the clinical use of 3D printing technology for the modelling of individual applicators for advanced gynecological tumors in magnetic resonance imaging (MRI)-based brachytherapy (BT). Material and methods: We tested individually designed 3D-printed applicators in nine patients with advanced gynecological cancer. Before BT was performed, all patients were treated with external beam radiotherapy (EBRT). The most common indication for individualized BT was advanced gynecological tumors where the use of standard BT applicators was not feasible. Other indications were suboptimal dose-volume histogram (DVH) parameters for high-risk clinical target volume (CTV-T-HR) at the first BT (V-100 <= 90% of CTV-T-HR volume and D-98 <= 80%, D-90 <= 100%, and D-100 <= 60% of dose aim). The EQD(2) dose aim to the target volume D-90 CTV-T-HR per one BT fraction was 20 Gy for cervical or recurrent endometrial cancer and 16 Gy for vaginal cancer patient. The first BT with the standard applicator in situ was used as the virtual plan for designing a 3D-printed applicator. The next BT was performed with a 3D-printed applicator in situ. The primary endpoint was to improve CTV-T-HR DVH parameters without exceeding the dose to the organs at risk (OARs). Results: All DVH parameters for CTV-T-HR were significantly higher with the use of an individually designed applicator. Mean D-90 CTV-T-HR improved from 14.1 +/- 5.4 Gy to 22.0 +/- 2.5 Gy and from 7.1 Gy to 16.2 Gy for cervical/recurrent endometrial and vaginal cancer, respectively (p < 0.001). The mean D-2cm3 bladder, rectum, sigmoid, and bowel dose was within institutional dose constraints, and increased from 13.0 +/- 1.5 Gy to 13.6 +/- 1.5 Gy (p = 0.045), 10.8 +/- 1.2 Gy to 11.7 +/- 1.3 Gy (p = 0.004), 8.9 +/- 3.2 Gy to 10.3 +/- 3.3 Gy (p = 0.008), and 8.7 +/- 3.8 Gy to 9.2 +/- 3.1 Gy (p = 0.2). Conclusions: With the use of individual 3D-printed applicators, all DVH parameters for CTV-T-HR significantly improved without compromising the dose constraints for the OARs.