Development of a low-cost 3D-printed phantom for end-to-end testing of model-based dose calculation algorithms (MBDCAs) in high-dose-rate (HDR) brachytherapy

Model-Based Dose Calculation Algorithms (MBDCAs), such as AcurosBV, have improved dosimetric accuracy in high-dose-rate (HDR) brachytherapy by accounting for medium heterogeneities and variations in scatter conditions. However, their safe and effective clinical implementation requires thorough commissioning, of which end-to-end (E2E) validation using physical phantoms is an important component. Commercial anthropomorphic phantoms can be costly and may offer limited flexibility for customized testing configurations.

This study aims to design, fabricate, and evaluate a novel low-cost, modular, 3D-printed phantom for E2E validation of MBDCAs in HDR brachytherapy. The phantom was developed to provide a practical, measurement-based tool for commissioning and quality assurance under controlled heterogeneous conditions, particularly in resource-limited settings.

A modular phantom incorporating heterogeneity plugs (moderate-density, air cavity, and calcium carbonate) was 3D printed using Polylactic acid (PLA) on a Bambu X1 Carbon printer. EBT4 films were scanned on an Epson 10000XL flatbed scanner, calibrated and used for planar dose measurements. The phantom was scanned with a Siemens CT simulator. Treatment plans were generated using BrachyVision in Eclipse v16.1, with dose distributions calculated using both TG-43 and AcurosBV algorithms. The plan was delivered with a GammaMed Plus iX afterloader. Film measurements were compared against calculated dose maps using gamma analysis and dose profile comparisons.

The 3D-printed phantom demonstrated high dimensional fidelity (± 0.15 mm) and allowed for reproducible catheter placement and film positioning. AcurosBV calculations showed close agreement with film measurements, with gamma passing rates of 95% at 2%/2 mm criterion and 94.2% at 3%/1 mm criterion. Mean dose differences between AcurosBV and film were 1.7% ± 1.9% for the vertical profile and -0.5% ± 1.7% for the horizontal profile. Under the controlled heterogeneous configuration of the 3D-printed phantom, TG-43 predicted higher doses than film by 3.6% ± 1.2% and 8.2% ± 1.5% for the vertical and horizontal profiles, respectively. These differences reflect the combined influence of the non-water-equivalent phantom body and the incorporated heterogeneous inserts.

This low-cost, modular, 3D-printed phantom provides a practical platform for E2E validation of MBDCAs under controlled heterogeneous conditions. Its customizable design may complement existing commissioning methods, particularly in resource-limited settings.