Desley van Zoggel

Chapter 8 144 irradiation followed by resection with curative intent was analysed. A total of 124 patients were selected. There was a moderate level of agreement (k = 0.52; 95 percent CI 0.36-0.68) when comparing good (mrTRG 1-2, Mandard 1-2) and intermediate/poor responders (mrTRG3-5,Mandard3-5). Interval between lastMRI andsurgery influenced the accuracy of the assessment. Agreement between pathologic response and mrTRG in patients with a long interval betweenMRI and surgery (i.e. >7weeks, n= 61) resulted in a fair agreement (k = 0.34, 95 percent CI 0.12-0.56), whereas the agreement was good in patients with a short interval (≤7 weeks; n = 63; k = 0.69, 95 percent CI 0.49-0.90). Overall, the mrTRG had a positive predictive value for good pathologic response of 95 percent when assessed by the lead radiologist; underestimation of the presence of residual tumour occurred in only one patient. This suggest that the mrTRG score has the potential to safely predict good responders, and perhaps offers an opportunity for a wait-and-see strategy in LRRC. After surgery for the primary tumour and repeated neoadjuvant treatment, remaining vital tumour can be difficult to select on MRI. PET/CT might be used to monitor the metabolic changes that occur following these neoadjuvant treatment strategies and might predict histopathological response. In chapter 7 a study is presented that aimed to analyse the correlation between PET/CT response and final histopathological outcomes in LRRC patients following treatment with induction chemotherapy. A total of 106 patients were included. All patients were monitored with pre-treatment and post-treatment PET/CT and went on to undergo surgery. On visual qualitative analysis, 24 (23 percent) of patients had a complete metabolic response, 54 (51 percent) had a partial metabolic response, and 28 (26 percent) had no response. A very important finding was that PET/CT response was a significant predictor of clear resection margins. Clear resection margins rates were 96 percent for complete metabolic responders, 69 percent for partial metabolic responders, and 50 percent for patients with no response. The sensitivity to detect major histopathological responsewas 42 percent, and the positive predictive valuewas 63 percent. A longer interval between post-treatment PET/CT and surgery negatively influenced the predictive value. The association between visual PET/CT response evaluation and the histopathological response is not strong enough to make definitive clinical decisions, but it proves to be an alternative for the direct visualisation of rectal cancer and is a complementary technique to aid in decision-making inmultidisciplinary tumour board meetings.