Page 124 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

Figure 7.1A | Left) Rigid registration of the cranial-caudal position of the right diaphragm (inside the red box) in all breathing phases. Right) The difference between the most extreme translations was defined as the amplitude (A4DCT).
Figure 7.1B | Amsterdam Shroud (AS) method to manually track the CC diaphragm position in CBCT projection images. a) Region of interest (red box). b) CC gradient filter applied and sum of all pixels creates a 1D image. C) This is repeated for all projection images, creating a 2D image. d) Detection of diaphragm positions in inhale and exhale breathing phases. e) Pixel coordinates translated to CC position. The amplitude was defined as the displacement between averaged end-inspiration and end-expiration diaphragm positions (ACBCT).
Statistical analysis
In order to determine whether respiratory-induced diaphragm motion observed in a single pre- treatment 4DCT accurately predicted respiratory-induced diaphragm motion during the treatment course, we tested for each patient separately whether ACBCT over all CBCTs differed from A4DCT using a one-sample t-test (significance level p<0.05). For each patient, we calculated the absolute differences between A4DCT and each ACBCT, and determined for which fractions the difference was larger than 3 mm (4DCT slice thickness is 2.5 mm).
To investigate possible time trends for each patient, we applied a linear regression analysis on ACBCT over the course of treatment. We also calculated the interfractional variability of ACBCT per patient (i.e., the SD over ACBCT). The diaphragm position on the averaged pre-treatment 4DCT (this is the averaged scan, based on all phases of the 4DCT) was considered as a reference (i.e., baseline), for which a rigid registration on bony anatomy was taken into account. We then calculated for each patient separately shifts of the diaphragm position in CC direction (i.e., the average position of the diaphragm during one CBCT) over the course of treatment. We used a one-sample t-test to test
121