A Novel 3D-Printing Process for a Tissue-Equivalent Phantom for Single-Isocenter Multi-Target Stereotactic Radiosurgery
Abstract
Purpose
The aims of this project were to (1) develop and apply a process to optimize 3D-printing processes specifically for tissue-equivalent small-field dosimetry phantoms and, (2) design and test a 3D-printed phantom for single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) dose verification.
Methods
The phantom was constructed with 3D-printed Polylactic Acid (PLA). Tissue equivalence was optimized for small field dosimetry by varying infill density, matching depth-dose and output factor measurements in PLA to Plastic Water (PW) for photon energies 6X, 6FFF and 10FFF and field sizes 4x4, 2x2 and 1x1 cm2. The phantom was custom designed as a 20 cm diameter sphere, comprising multiple 3D-printed components, with an interchangeable detector insert (ion chamber or Gafchromic film). Four spherical air cavities (4 mm diameter) were built into the phantom to facilitate image-based phantom setup. Phantom validation involved static-gantry, dynamic-conformal-arc (DCAT) and nine SIMT SRS volumetric modulated arc therapy (VMAT) plans using a small-volume ionization chamber and film. Doses were compared to measurements in PW and treatment planning system (TPS) calculations.
Results
Static-gantry measurements in the 3D-printed phantom agreed with PW to within ±1%, while DCAT measurements agreed with TPS doses to within ±2.5% for all energies and field sizes. The SIMT SRS VMAT film-measured dose planes compared to TPS dose planes yielded a mean gamma pass rate (5%/1.5mm) of 98.5% (range: 92.4%-100%) and a mean point dose difference of 1.9% (standard deviation: 2.8%).
Conclusion
This study demonstrates that the novel 3D-printed phantom provides a cost-effective, tissue-equivalent solution for SIMT SRS dose verification. The design allows customisation for a range of detector types and measurement configurations and can be readily manufactured at centres with access to standard 3D-printing facilities. As such, the phantom represents a practical and accessible tool for commissioning and patient-specific quality assurance of SIMT SRS treatment plans.