Room: Karl Dean Ballroom A1
Purpose: Contrast enhanced radiotherapy (CERT) could improve outcomes in high grade gliomas, but current research into CERT is either prohibitively expensive, restricted to small field sizes, or without photoelectric enhancement. This work establishes the first reported development of kilovoltage intensity modulated radiotherapy (kIMR), which we theorize could be safely utilized in large brain tumors for conformal CERT despite the presence of the skull.
Methods: A miniaturized MLC was designed and constructed with tungsten carbide rods, 3D printed gear rack, and a low friction design. The MLC is controlled by an in-house GUI written in Qt to drive stepper motors using custom circuitry through an Arduino Uno microcontroller. An Indico 100 x-ray tube was filtered by 0.1mm tungsten and a 3D printed flattening filter. The MLC is mounted between this x-ray tube and isocenter, which was marked by a laser system. Phantoms were loaded with EBT3 radiochromic film, placed on a treatment couch, and rotated about isocenter to simulate gantry rotation. Treatment plans were created in Eclipse and delivered on the Lucy and Rando phantoms using 3D conformal, IMRT, and noncoplanar techniques.
Results: After commissioning the MLC and calibrating the radiochromic film with a time scaled relative index, surface dose was compared to the maximum dose measured on each film. These measurements are, predictably, worse than those in a megavoltage beam, but are still reasonable (about 0.37-0.54). IMRT and noncoplanar falloffs are more sparing than 3D conformal falloff. More promising, dose at depth in the Rando head was found to be reasonable despite having to penetrate a skull.
Conclusion: Measured dose falloff is acceptable and, while not as steep as conventional megavoltage treatments, can deliver a clinically acceptable distribution even through a heterogeneous, anatomically accurate phantom. It is reasonable to pursue this modality further to complement CERT in large brain tumors.
Low Energy X-rays, MLC, Radiation Therapy