Room: Exhibit Hall
Purpose: Advanced radiotherapy techniques require the use of complex immobilization devices that need to be accurately accounted for in the treatment plan and commissioned and evaluated for dosimetric impact. The purpose of this work was to develop methodologies to characterize radiological properties of various materials used in immobilization for radiation therapy over various photon energies.
Methods: A narrow beam geometry setup was used in conjunction with a mini-phantom in order to measure transmission fluence for various photon energies (6, 10, 15 & 18 MV) generated from a Varian TrueBeamÂ® linac. Care was taken to minimize scatter generated from the material and from the room itself. Several different types of materials were evaluated: Solid waterÂ® (Gammex), carbon fiber (Klarity) and a new support material K-Liteâ„¢ (Klarity). Given the variable densities between and within each material, the linear attenuation values were normalized based on density. All materials were also CT scanned to determine HU values.
Results: Attenuation coefficients (Âµ/Ï?) values were determined and compared between materials. Compared to solid waterÂ® across the energies measured, K-Liteâ„¢ has Âµ/Ï? values between 106.2 and 106.9% of solid water, while the carbon fiber had Âµ/Ï? values between 92.1-93.7% of solid water.
Conclusion: Attenuation measurements provide a reasonable and systematic method to compare immobilization device materials for their usefulness in radiation therapy.