SU-E-T-101: An Arc Based Treatment Technique for Proton PBS Beam Utilizing Overlaid Bragg Peak Spots




When Bragg peaks from proton PBS beams are overlaid from a large number of directions, it creates a localized dose distribution with rapid falloff. By positioning these overlaid Bragg peak (OBP) spots strategically throughout the targeted volume, a uniform and conformal dose distribution can be achieved. When PBS spots from all the directions are delivered in an arc fashion, it becomes the Volume Modulated Proton Therapy (VMPT) technique which corresponds to the VMAT technique in photon therapy.


PBS beam from an IBA machine and a 20cm radius cylindrical phantom were simulated with GATE/GEANT4. To position the OBP spot at the center of the phantom, single energy PBS beam from 10/36/360 equally-spaced directions around the phantom was used. To position the OBP spot at an off-center position, PBS beams with various energies were used. To form a uniform dose distribution in 1D/2D, OBP spots are positioned in arrays with spot intervals and weight optimized.


Dose profile for single energy OBP spot improved when the number of beam angles increased from 10 to 36, but remained same from 36 to 360 angles. Multi-energy OBP spot had a slightly non-symmetrical profile due to the different energy proton beams used. By optimizing each OBP spot's weight, 11 OBP spots with 10mm interval size created a uniform dose distribution covering a length of 10cm. Similarly, 11×11 OBP spots in an array of 10mm interval size created a uniform dose distribution covering an area of 10×10cm2.


We demonstrated the technique of using OBP spots to deliver uniform dose in 1D/2D. This technique can be easily extended through the optimization of position and weight of OBP spots in 3D and becomes the arc based VMPT technique. Further studies are needed to explore the optimization methods and full potential of the VMPT technique.