Purpose: To design and 3D-print a phantom to perform daily QA on proton therapy machines for a low and a high energy.
Methods: A water-equivalent phantom was designed with two towers of heights corresponding to the depths of 70% dose of two proton beam energies that were determined using the depth dose data obtained during beam commissioning. For E=104MeV, the tower height=7.3cm, and for E=183MeV, the tower height=21.8cm. These towers are located on a 18x18x2cm³ base. The x- and y- axes of the base are used for flatness and symmetry measurements. The phantom was 3D-printed using PLA material and a Raise3D Pro Plus 3D Printer. For daily QA, the phantom is placed on an IBA I’mRT MatriXX multi-ionization detector. The IBA MatriXX allows charge readings for individual ion chambers at certain circular areas based on an electron dosimetry energy plate. We setup the phantom on the MatriXX such that the two towers are positioned above these areas in order to assess dose. For each energy, the ratio of the charge reading beneath the corresponding tower to the central axis (under 2.6cm of water-equivalent material) is determined. This ratio is constant and any deviation from this constant when performing daily QA shows the change in beam energy (range). Our criterion for range variation is ±1mm.
Results: A phantom was successfully 3D-printed with towers corresponding to the 70% depth dose of proton beams of 104 MeV and 183 MeV. The phantom can be used for energy verification along with flatness and symmetry measurements for daily QA.
Conclusion: A two-energy phantom can be 3D-printed for daily QA for proton beams. This method can be extended to perform QA for more energies with the addition of more towers.
3D, Phantoms, Quality Assurance
TH- External Beam- Particle/high LET therapy: Proton therapy – quality assurance