Mesorectum volumetry in males with rectal cancer: Variabilities observed in pre- and post-neoadjuvant radiotherapy imaging

This study utilised magnetic resonance imaging (MRI) to describe the within population variations and the variability observed in the volumetry of the mesorectum pre- and post-neoadjuvant radiotherapy, prior to surgical intervention, in a South-African sample of males with rectal cancer. Nineteen pelvic MRI scans of males diagnosed with rectal cancer, who underwent neoadjuvant l ong course radiotherapy (LCRT) or short course radiotherapy (SCRT) prior to undergoing a total mesorectal excision (TME), were retrospectively reviewed and analysed. Mesorectal volume was calculated after contouring individual axial slices and creating a three-dimensional compounded structure on both pre- and post-radiotherapy scans, which were subsequently described and compared. Both pre- and post-neoadjuvant radiotherapy mesorectal volumetry displayed great variability. Mean calculated pre-radiotherapy mesorectal volume was 272.94 ± 80.30 cm 3 . Post-radiotherapy volume equated to 239.19 ± 81.30 cm 3 , presenting an overall percentage decrease of 12,60%, resulting in a statistically significant difference (p=0.001). In sub-group analysis, both patient groups who underwent LCRT and SCRT showed a general decrease and statistically significant difference in mesorectal volume post-radiotherapy when compared to pre-radiotherapy imaging. Significant variation in the volumetry of the mesorectum pre- and post-neoadjuvant radiotherapy observable on MRI can have important clinical implications for the TME. A change in mesorectal morphometry may require modification of the planned surgical strategy. Therefore, the information obtained from a post-radiotherapy MRI prior to surgical intervention, can be a worthwhile addition to the available armamentarium for surgeons to guide surgical decision-making, encouraging the adoption of optimal individualized and novel treatment strategies to improve patient outcomes. • The mesorectum holds significant clinical implications in rectal cancer patients. • Mesorectal volumetry displayed great within population variation pre-radiotherapy. • Significant variation between pre- and-post radiotherapy volumes was also seen. • MRI can detect these variations pre-operatively and guide surgical planning. • Thus, acknowledgement of variations can aid in promoting optimal patient outcomes.