# Incorporating Clinical Imaging into the Delivery of Microbeam Radiation Therapy
## 3 Results and Discussion  
### CT Scans and Associated Dosimetry  
Balancing scan time, iodine clearance and image resolution, scans on the Inveon Multimodality System were found to be optimal with 142 projections, each 200 ms at 80 kVp. Total imaging time is 10 min. The resulting image provides 97 um \(\times\) 97 um \(\times\) 97 um voxel resolution of a 9 cm \(\times\) 9 cm \(\times\) 9 cm volume. The 10 cm bore of the scanner limits suitability for imaging larger animals. The Siemens SOMATOM go.Up scanner was found to be optimal operating at 42 mA at 80 to 110 kVp, using the minimum available 0.6 mm slice thickness. Imaging time is drastically shorter with a volume of 51 cm \(\times\) 51 cm \(\times\) 20 cm imaged in 15 s. The reconstructed image provides a 300 um \(\times\) 300 um \(\times\) 300 um voxel resolution. The large 70 cm bore makes this scanner suitable for imaging larger animals or humans. The greatly reduced time per scan and maximum patient size of the Siemens SOMATOM go.Up come at the cost of decreased spatial resolution compared with the Inveon Multimodality System as highlighted in Figure 4. Despite the decreased resolution, as the tumour volume and skeletal landmarks are easily identifiable, the Siemens SOMATOM go.Up was the scanner chosen for image-guided MRT in this work. After imaging the simple bone and water small animal phantom, partially filled with 1 ml of 2 mg/mL iodine in water solution. Scans were reconstructed using all available reconstruction kernels. Peak X-ray energy was not a major contributor to image quality, with average standard deviation of pixel values in a uniform \(20\,\mathrm{mm}\times 20\,\mathrm{mm}\times 20\,\mathrm{mm}\) region (noise) of Solid Water(r) at the centre of the phantom showing little difference from 9.6% for the lower energy 80 kVP scans and a standard deviation of 11.7% for the higher energy 110 kVp scans. Selecting the reconstruction kernel is one of the few ways a user may influence the image reconstruction process of a clinical CT scanner. The selection of reconstruction kernel is a trade-off, with smoother filters lowering noise at the cost of reduced resolution. In our scans, we found the choice of reconstruction kernel greatly affected image noise, resolution and material contrast. The available reconstructions are ranked in Figure 5, with equal importance on minimising noise and maximising the contrast between regions of Solid Water(r) and iodine solution. With the assumption that high contrast and low noise image would make manual tumour identification easiest. From this, the optimal reconstruction kernels are deemed to be BV40 and HV40, with both kernels producing almost identical reconstructions. Radiographic imaging increases the radiation dose to the patient, in ways other than the intended treatment. To minimise the potential for negative effects due to imaging, this dose must be reduced as much as possible. Figure 4: Sagittal reconstruction of rat comparing CT scan image quality. Inveon Multimodality System with \(97\,\mathrm{\SIUnitSymbolMicro m}\times 97\,\mathrm{\SIUnitSymbolMicro m}\times 97\, \mathrm{\SIUnitSymbolMicro m}\) voxel resolution (**left**) and Siemens SOMATOM go.Up with \(300\,\mathrm{\SIUnitSymbolMicro m}\times 300\,\mathrm{\SIUnitSymbolMicro m}\times 300\, \mathrm{\SIUnitSymbolMicro m}\) voxel resolution (**right**). The CT scanning process as outlined for the Inveon Multimodality System resulted in a skin dose of \((8.63\pm 0.43)\) cGy as measured with the MOSkin(tm) detector and a dose of \((7.24\pm 0.29)\) cGy at \(12.5\,\mathrm{mm}\) depth within a \(25\,\mathrm{mm}\times 25\,\mathrm{mm}\times 55\,\mathrm{mm}\) phantom as measured with the PTW PinPoint(tm) ion chamber. The CT scanning process as outlined for the SOMATOM go.Up resulted in a skin dose of \((1.39\pm 0.08)\) cGy as measured with the MOSkin(tm) detector and a dose of \((1.30\pm 0.05)\) cGy at \(12.5\,\mathrm{mm}\) depth within a \(25\,\mathrm{mm}\times 25\,\mathrm{mm}\times 55\,\mathrm{mm}\) phantom as measured with the PTW PinPoint(tm) ion chamber.