Deviation of the upper, middle and lower thirds of the rectum during irradiation of rectum cancer

Abstract

Background. In patients with rectal cancer, daily variations in rectal volume often lead to large deformations of the target volume that cannot be corrected by adjusting the radiation couch. The main purpose of the study was to determine the deviation of all three thirds of the rectum from the reference position and to determine whether these deviations were influenced by the alignments to the bony structures (the sacrum) and the posterior rectal wall.

Materials and methods. The conduct of the study was divided into the review of the database, contouring of the anatomical structures on the CBCT images, data acquisition of the deviations and data output, with the alignment to the bony structures (the sacrum) - and the alignment to the posterior rectal wall performed separately.

Results. Fifty preoperatively irradiated patients were included in the study. The analysis revealed statistically significant differences in terms of alignment with the bone structures for different variations of the rectal thirds in the directions anterior +, posterior +, posterior –, left –, right + and right –. Regarding the alignment to the posterior rectal wall, the analysis showed statistically significant differences for different variations of the rectal thirds in anterior +, posterior +, posterior –, left –, right +, right – and bones +.

Conclusions. The position of the rectal thirds changes daily in alignment with the bony structures (the sacrum), as well as in alignment with the posterior rectal wall.