SU‐E‐T‐452: Dynamic Intensity Modulator

Purpose: To reduce the radiotherapy treatment time per freaction in order to decrease the possibility of patient movement during treatment and increase patient comfort. Methods: A prototype of a Dynamic Intensity Modulator (DIM) was created which changes fluence profiles dynamically and autonomously between treatment grantry angles. Radiation Absorbing Material (RAM) is dynamically displaced in and out of the radiation beam path by radio‐translucent columns. A reservoir regulates the amount of RAM in the beam path. Between gantry angles columns shift to create new fluence profiles. Measurements of beam fluence were acquired using portal images for various RAM thicknesses. Results: Imaging varying RAM thicknesses shows definite changes in image intensity. Initially the columns were at the zero position, so a constant height layer of RAM was achieved. By comparing a constant height layer of RAM against a thicker constant height layer of RAM, an increase in attenuation was observed. Different columns height configurations were also tested. Again, areas with a thicker layer of RAM had a higher level of attenuation than areas with a thinner layer of RAM. In all tests the prototype columns used to set the height of RAM were visible. This will be resolved by creating columns, which are more radio‐translucent. Also, a significant amount of noise was visible in the attenuation profiles. This was most likely due to the material choice of RAM, a homogenous mixture of 2 different diameter lead BB's. Conclusions: Despite the non‐uniformity within intensity profiles, this study demonstrates the fundamental concept of the DIM. The prototype was able to displace deformable RAM in different locations to create distinct fluence profiles.