Introduction: Rectal tumors are divided into three subgroups according to the location or height of their origin: the lower, middle and upper third of the rectum. In patients with rectal cancer and in patients with other pelvic malignancies, daily variations in rectal and bladder volume often result in large deformations of target volumes that cannot be corrected by adjusting the radiation couch. Purpose: The aim of the Master's thesis was to obtain a comprehensive insight into the movement of the rectum in the upper, middle and lower third during neoadjuvant irradiation in patients with rectal carcinoma. Methods: Fifty preoperatively irradiated patients were included in the study. The implementation of the research was divided into four main parts: database review, drawing of anatomical structures on CBCT images, data collection of deviations and data output, where alignment to bone structures – the sacrum and alignment to the posterior rectal wall were performed separately. The final stage included statistical analysis and data processing. Results: The analysis revealed that there are statistically significant differences in the posterior, left and right directions when aligning to the bone structures – sacrum, while when aligning to the posterior rectal wall there are statistically significant differences in the left and right directions. When determining the difference between the alignments to the bone structures – sacrum/posterior rectal wall, we noticed that there were statistically significant differences in the left direction and in the bone structures. Deviations were mutually different in the upper, middle and lower third of the rectum. The greatest deviation was expressed in the upper, followed by the middle and then the lower third of the rectum. The analysis of the diameter of the rectum along the X and Y axes showed that the daily value of the rectum can be greater or less than the reference value, which indicates a daily variation in the rectal filling. The results of the analysis of the variations between the daily and reference volumes of the rectum and urinary bladder showed that the daily rectal volume is, on average, smaller than the reference volume by 2 cm3, while the bladder volume, on average, is smaller than the reference bladder volume by 10 cm3. Discussion and conclusion: The position of the rectum in the upper, middle and lower thirds changes daily in alignment with the bone structures – sacrum, as well as in alignment with the posterior rectal wall.
|