Small animal irradiation using the MARS Spectral CT
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This thesis reports on a novel use of the Medipix All Resolution System (MARS) Spectral CT scanner as a platform of small animal irradiation. Irradiation from the x-ray source in the scanner was used to inhibit the growth and recovery of neurons in rats. The goal is to extrapolate the relationship between stem cells and memory and functional behaviours. Specific developments were carried out prior to the irradiation of live rats. A live rat holder was designed and built to provide a setup stable enough for fixing the position of the rats head. This was achieved by integrating a three piece bar system into the holder to hold the head from both ears and nose. To quantify the absorbed dose, x-ray exposures were measured using a calibrated ion chamber and were used to generate a depth dose curve with sheets of Perspex layers and radiochromic films. This curve is presumed to simulate the dose inside the rat‘s head.
To target a sub region of interest within the rat‘s brain, specific anatomical landmarks were investigated for the design of the lead collimators. The position of the sub volume, the hippocampus, was located through a combination of anatomical landmarks and x-ray transmission images of the rat‘s head. Bregma and the interaural line were used to numerically plot out the co-ordinates of the dorsal and ventral hippocampus which was then translated onto the lead collimators.
The x-ray transmission images of euthanized rats were used as a guide to locate the dorsal and ventral hippocampuses. Bregma and the interaural line were the main anatomical landmarks which were used for the design of the lead collimators to be placed around the head. Three pilot rats were irradiated with the designed holder and collimators. The point dose to the hippocampus was calculated using the simulated depth dose curve. Post irradiation status of the neurogenesis was assessed three weeks after the treatment. However only one of the three rats showed a significant reduction in the number of neurons in the hippocampus emphasizing the room for more improvement in the physical setup of the irradiation.