Evaluación del efecto cicatrizante

Figure 8: Localising data points related to tumour using original CT scan spatial co-ordinates. 3 points extracted and plotted back in the texture map using the scan co-ordinates.

Figure 8 shows 3 points from the high density, low entropy region of the texture analysis data plot. All 3 are in the tumour. Figure 9 shows the sub-analysis of a different region, which appears to relate to the edge of the liver.

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Figure 9, Localising data points related to liver edge using original CT scan spatial co-ordinates. texture analysis data plot, with 3 points extracted and plotted back in the texture map using the scan co-ordinates.

Figure 8 and 9 suggest that this tool is helpful as it can generate hypotheses. It suggests that the high density, low entropy region of the texture analysis plot is consistent with the tumour, however unless all data points in the plot are included, it is difficult to prove this conclusively.

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5.1.6 Experiment 17: Multiple point region of interest analysis

Aim: This experiment aimed to investigate the regions of interest of the texture analysis data plot from the AVIP (Average Intensity Projection) phase of the pre-treatment radiotherapy planning CT scan of the ipsilateral lung to a primary lung tumour. The hypothesis for this experiment was that the majority of tumours contain a low entropy region, meaning the tumour is likely to be in the low entropy high density region of the texture analysis data plot. Methods: 15 patients who received SABR had the lung containing tumour segmented from the AVIP phase of the 4DCT scan. This was then analysed. The region of interest tool was then set to plot all points with a density of 900-1200 and an entropy score of 2 or less. This region was then converted into a Niftii file and overlaid with a Niftii file of the texture map of the whole lung in ITK-SNAP (Yushkevich et al., 2006).

Results and Discussion: Image c) in figure 10 shows how the sub-region of the texture plot overlaps with the low entropy region of the tumour. The original CT image and texture map can be seen in a) and b) respectively. Figure 10 also shows the region of the data plot, which was analysed and overlaid with the original texture map. Image c) shows that the sub region identified in red overlaps neatly with the original texture map.

Figure 11 shows this comparison extended to 15 primary lung tumours overlap of the sub region (density 900-1200 and entropy 2 or less, seen in red). In 13 of 15 tumours this region overlaps with the tumour. This was a pictorial, rather than numerical analysis, but shows convincingly that the tumour sub region of the entire data plot can be predicted in the majority of tumours. What is not shown in figure 29, is that in some of the data plots other structures were included in the sub-region of the data plot, which were analysed. These were consistently larger blood vessels containing IV contrast.

The results of this experiment are shown in figure 10. It shows that the central homogeneous region of the tumour consistently overlaps with the structure generated by segmenting the tip of the high density low entropy tip of the texture analysis data plot, as described in the methods of experiment 17.

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Figure 10: Overlaying the tip of the trunk in the elephant plot with the original texture map of the whole lung for 1 patient before treatment. Image a) shows the original CT image containing a primary lung tumour, image b) illustrates the texture map generated from the CT data. Image c) shows a red region representing the sub region of the texture map including data points with an entropy score of 2 or less and a density score of 900-1200 overlaid over the texture map. The data plots show the sub-region that was analysed.

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Figure 11: Overlaying the tip of the trunk in the elephant plot with the original texture map of the whole lung for 15 patients from the AVIP phase of 4DCT planning scan before SABR treatment. The tip of trunk defined as points included with a density score of 900-1200 and entropy score of 2 or less, region of texture analysis data plot with texture map for 10 primary lung tumours treated with SABR. The images were generated by overlaying 2 texture maps, one from the whole texture map in white and the second in red as the sub- region of interest. The 7th _{image did not contain data points within the sub-region os appears} much brighter than the other images.

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5.1.7 Experiment 18: Understanding use of different phases of pre-treatment analyses Aim: From previous experiments it was determined that it was possible to produce a texture analysis data plot for an entire lung. Experiment 17 showed it was possible to identify the tumour within the data plot. However, as the size of the analysed area had increased significantly since earlier experimental work, it was not clear what effect different phases of the 4DCT had on the texture analysis of an entire lung, as experiment 4 had only focused on the GTV. This was investigated to understand what effect movement had on the appearance of the pre-treatment elephant plot.

Radiotherapy planning of lung tumours uses a multi-phase 4 dimensional CT scan. When a patient is scanned, the patient completes a breathing cycle for every 2cm scanned. The patient is breathing comfortably during the scan, they are not aiming to maximally inspire and expire. The scan software generates 10 phases, CT0, CT10, CT20 etc. to CT90. CT0 is end inspiration and CT50 is end expiration. Between CT0 to CT50 the patient is breathing out and between CT50 and CT0 the patient is breathing in. Two composite volumes are generated. The AVIP (Average Intensity Projection) is the average image, the MIP (Maximum Intensity Projection) is the maximum density experienced during the breathing cycle within each voxel. Standard practice is to outline all structures on the AVIP, but take account of tumour motion on the MIP. It is important to understand how different phases affect the texture plot of the whole lung so that any confounding variables can be adjusted for. Patients undergo different scans in different breathing phases. The CT of the PET-CT is a single image series performed with the patient in free breathing, for planning the CT is performed with multiple phases and most diagnostic and post treatment scans are performed in inspiration breath hold.

Experiment 18 Methods: A single patient was used for this analysis. The radiotherapy