Image guided conformal small animal orthovoltage microirradiators are currently under development to perform radiobiological experiments with preclinical cancer models. An important component of these instruments is the treatment delivery image guidance system, a microelectronic portal imaging device (μEPID). Here, we present the design and implementation of a μEPID, specifically designed and constructed for small animal orthovoltage microirradiators. The μEPID can acquire images in the range of 60 kVp to 320 kVp x-ray photon energies and can endure high doses from orthovoltage beams without radiation damage. The μEPID can acquire 200 μm resolution images at a rate of 17 frames per second for online in vivo co-registration between irradiation beams and small animal anatomy. An exposure with less than 1% of a 2 Gy treatment field is required for imaging, which is an adequate ratio between imaging dose and treatment dose to avoid undesired irradiation of healthy tissue or alteration of the preclinical cancer model. The μEPID was calibrated for microdosimetry with a precision of 4.1% with respect to an ion chamber, used as a gold standard. To validate the in vivo device performance, irradiations of lung, brain, and xenograft breast cancer preclinical models were performed and analyzed.
Keywords: Preclinical radiobiology; high resolution imaging; microirradiator; orthovoltage imaging.