Design of a Patient-Specific Cranial Phantom (PSCP) for Evaluation Across Multiple Dosimetric Systems in Linac-Based Stereotactic Radiosurgery

INTRODUCTION: In this study, a patient-specific cranial phantom (PSCP) was fabricated using 3D printing technology and its usability in individual quality control processes instead of commercially available 2D/3D phantoms was evaluated.
METHODS: Three patient-specific phantoms (PSCP1, PSCP2 and PSCP3) were modelled using computed tomography (CT) data from three different patients and fabricated using a plant-based biopolymer (STH). RTV2 silicone or paraffin wax were used to represent brain tissue. The quality and dosimetric reliability of the phantoms were analysed using point dose measurements with metal oxide silicon field effect transistor (MOSFET) and beryllium oxide (BeO) dosimetry systems on a Trilogy® radiotherapy machine and compared with treatment planning system (TPS) data.
RESULTS: The HU value of neurocranial bones fabricated with 100% infill STH filament was 141 ± 16.7. Silicone and paraffin wax brain tissue surrogates yielded HU values of 33 ± 6.4 and −56 ± 12.8, respectively, compared with 22 ± 4.4 for real brain tissue. In MOSFET measurements, dose differences ranged from 0.25% to 7.78%, while BeO dosimetry showed differences between 2.28% and 7.81%. Across both dosimetry systems, S-VMAT plans consistently produced lower measured doses, whereas higher values were observed with M-VMAT. Point dose analysis revealed a statistically significant difference between S-VMAT and M-VMAT techniques for both brain tissue materials, regardless of lesion number (p < 0.05), indicating a systematic planning-related effect.
DISCUSSION AND CONCLUSION: The obtained data demonstrate that the PSCP can be used as a mechanically stable and dosimetrically reliable model for patient-specific quality assurance by testing different planning techniques and dosimetry systems.

Keywords: 3D Printer, Silicone, Paraffin Wax, Beryllium Oxide (BeO), Metal Oxide Silicon Field Effect Transistor (MOSFET)