We were approached by an oncologist and molecular biologist to participate in a small startup, funded by Siemens, to explore a new approach to treating cancer. The basic idea was to inject contrast agent directly into tumors and then irradiate the tumor with x-rays. Contrast agent is an iodine- or barium-based substance that strongly absorbs x-rays; it is conventionally injected systemically when doing CT imaging to enhance the visibility of certain anatomical structures. The idea behind CERT is to use this preferential x-ray absorption to increase the x-ray dosage delivered to a tumor. It also allows lower-energy x-rays to be used (since those are the ones absorbed by the contrast agent) compared to conventional radiotherapy; this should drastically reduce treatment cost since expensive LINACs are not required. Since the team was small, our role in the project encompassed many different areas, including assisting with the treatment of both people and animals. However, our principal function was to develop, from scratch, a software suite that analyzed CT images before and after the injection of contrast, and determined a treatment profile (x-ray source location and intensity) in real time based on an analysis of the images. The CT images were converted to Hounsfield units and segmented into tissue types, from which a spatial distribution of x-ray absorption could be determined. This was critical in providing both an effective treatment (delivering enough x-rays to the right areas) and making it safe (not delivering too much dose). Our software platform as a PC running Linux and the user interface was written in GTK+.