The role of MRI after preoperative treatment of rectal cancer is unclear. This thesis investigates its diagnostic relevance in patient management.
Matching pathology with MR images aimed to characterise post treatment rectal cancer appearances on T2 weighted MRI and verify the proposed MRI tumour regression grading system(mrTRG). Correlation of post-chemoradiation mrTRG, T stage(ymrT), N stage(ymrN) and Circumferential Resection Margin(ymrCRM) with histopathological T stage(ypT), N stage (ypN), and pathological CRM(pCRM) was investigated. These parameters were also compared against survival outcomes.
The alternative response assessment methods of tumour volume and length change/RECIST as well as mrTRG and ymrT were evaluated against pathology. The accuracy and reproducibility of MRI parameters in assessing rectal cancer response to neoadjuvant chemotherapy was also investigated.
Patients with good response to chemoradiation(assessed by mrTRG) were enrolled into a deferral of surgery trial. Serial MRI-based monitoring enabled evaluation of quantitative imaging methods such as Apparent Diffusion Co-efficient (ADC) measurements in distinguishing tumour vs. complete response.
Pathological fibrosis correlated with low signal on MRI, tumour was intermediate signal. mrTRG showed good diagnostic accuracy against ypT&pTRG, ymrT’s diagnostic accuracy was fair but improved when grouped into favourable and unfavourable categories. MRI Length&volume assessment were less consistently related. Negative ymrN and potentially clear ymrCRM correlated well with their respective pathological endpoints. Importantly, mrTRG and ymrCRM involvement predicted survival outcomes.
mrTRG showed good diagnostic accuracy against pTRG when assessing neoadjuvant chemotherapy response, ymrT correlated less well. Overall mrTRG and ymrT were the most reproducible parameters. ADC values were significantly lower in patients with tumour vs. complete response with ADC measurement of <1.3X10-3/mm2/sec associated with tumour regrowth in 86% of cases.
mrTRG and MRI CRM assessment appear the most important post treatment imaging parameters. Grouped ymrT may also be useful. These parameters could be used by the multidisciplinary team to tailor treatment pre-operatively.