Purpose: Dosimetry with the GammaPod® breast radiosurgery device (Xcision Medical Systems, Inc, Columbia, MD) uses Poly(methyl methacrylate) (PMMA) material for reference dosimetry while using a water equivalent media with breast tissue density (~0.94 g/cm3) for clinical dosimetry. Direct measurements with the breast tissue equivalent material is desirable to reduce the error from converting the dose from a material to another. In this study we designed a 3D-printed breast-equivalent phantom and tested its dosimetry characteristics.
Methods: Based on previous publications, Acrylonitrile Butadiene Styrene (ABS) 3D printed phantoms with a 90% infill creates a material with a radiological effective density of 0.94 g/cm3. We a designed a phantom printed with ABS to fit within a typical stereotactic breast cups used for patient immobilization. A replaceable insert allows the placement of an A1SL ionization chamber in multiple positions within the phantom. In addition, a square block of material with the same infill was created to test the density of the material. GammaPod end-to-end tests were performed with the breast phantom by placing the phantom in the cup immobilization system and performing CT simulation and treatment planning as per a clinical patient. These plans were then delivered and the calculated doses compared to the radiation absorbed doses measured following the IAEA TRS 483 dosimetry protocol.
Results: The TPS doses agreed with the measured doses within 1%. These results have on the order of a 2-3% uncertainly due to the inherent uncertainties of the dosimetry protocol and the uncertainties of the 3D printing method in achieving the desired density.
Conclusion: This work has resulted in the creation of 3D printed breast density phantom that is capable verifying the TPS calculated dose of the GammaPod and serving as an end-to-end tool with the potential to greatly simplify the commissioning process.
Absolute Dosimetry, Breast, Phantoms
TH- Radiation Dose Measurement Devices: Phantoms for dosimetric measurement