Comprehensive Clinical Feasibility Assessment of Biomed Flex 50A Flexible Bolus Fabricated Using the Formlabs 4BL SLA Printing Platform
Poster
aapm2026_poster.pdf Hosted by AAPM · 0.7 MBAbstract
Purpose
To perform an integrated, translational feasibility assessment of patient-specific flexible bolus fabricated using the Formlabs 4BL stereolithography (SLA) platform with BioMed Flex 50A resin. The study aimed to interrogate geometric fidelity, CT-derived radiological behavior, material heterogeneity, and water-equivalent dosimetric performance to determine suitability for clinical radiotherapy workflows.
Methods
A cohort of twelve bolus geometries was fabricated and evaluated through a multiparametric geometric characterization pipeline incorporating precision metrology, volumetric CT segmentation, and high-density surface morphometric analysis via MeshLab point-cloud deviation mapping. Extracted metrics included dimensional deviation, spatial alignment error, and both mean and RMS Hausdorff distances. A computational MATLAB framework was developed to quantify intravolume material uniformity, incorporating automated couch-structure suppression, 2-mm morphological contour erosion to mitigate partial-volume effects, voxel-wise HU interrogation, and stratification of low- and high-density subregions. Water-equivalency was evaluated through comparative analysis of measured 5-, 10-, and 20-mm bolus thicknesses against Treatment Planning System (TPS) Effective Path Length (EPL) predictions and through photon/electron PDD perturbation characterization across relevant energies. End-to-end dosimetric validation was performed using a head phantom fitted with a 1-cm flexible bolus, enabling integrated assessment of TPS dose distributions, PTV statistics, isodose morphology, and surface-dose verification using optically stimulated luminescent dosimeters (OSLDs).
Results
Geometric accuracy was consistently sub-millimetric, with mean dimensional deviation 0.06 mm and all Hausdorff values <1 mm. Density analysis demonstrated stable, soft-tissue–equivalent HU distributions (~18–32 HU), absence of low-density defects, and limited localized overdensity. Bolus thicknesses showed high concordance with TPS EPL (differences ≤0.2 mm). PDD curves confirmed water-equivalent attenuation. Phantom evaluation demonstrated a ~1.3-cm buildup shift, improved mean PTV dose (93.9%→101.3%), and strong OSLD–TPS concordance (2.6–4.3%).
Conclusion
The Formlabs 4BL BioMed Flex 50A platform produces patient-specific flexible bolus with excellent geometric precision, radiological uniformity, and dosimetric reliability, supporting its integration into advanced radiotherapy practice.