MRI volumetry for prediction of tumour response to neoadjuvant chemotherapy followed by chemoradiotherapy in locally advanced rectal cancer

Objective: To investigate if MRI-assessed tumour volumetry correlates with histological tumour response to neoadjuvant chemotherapy (NACT) and subsequent chemoradiotherapy (CRT) in locally advanced rectal cancer (LARC). Methods: Data from 69 prospectively enrolled patients with LARC receiving NACT followed by CRT and radical surgery were analysed. Whole-tumour volumes were contoured in T-2 weighted MR images obtained pretreatment (V-PRE), after NACT (V-NACT) and after the full course of NACT followed by CRT (V-CRT). V-PRE, V-NACT and tumour volume changes relative to V-PRE, Delta V-NACT and Delta V-CRT were calculated and correlated to histological tumour regression grade (TRG). Results: 61% of good histological responders (TRG 1-2) to NACT followed by CRT were correctly predicted by combining V-PRE < 10.5cm(3), Delta V-NACT > -78.2% and V-NACT< 3.3cm(3). The highest accuracy was found for V-NACT, with 55.1% sensitivity given 100% specificity. The volume regression after completed NACT and CRT (V-CRT) was not significantly different between good and poor responders (TRG 1-2 vs TRG 3-5). Conclusion: MRI-assessed small tumour volumes after NACT correlated with good histological tumour response (TRG 1-2) to the completed course of NACT and CRT. Furthermore, by combining tumour volume measurements before, during and after NACT, more good responders were identified. Advances in knowledge: MRI volumetry may be a tool for early identification of good and poor responders to NACT followed by CRT and surgery in LARC in order to aid more individualized, multimodal treatment.