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 T2 weighted MR images obtained pre-treatment (VPRE), after NACT (VNACT) and after the full course of NACT followed by CRT (VCRT). VPRE, VNACT and tumour volume changes relative to VPRE, ΔVNACT and ΔVCRT 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 VPRE < 10.5 cm(3), ΔVNACT > -78.2% and VNACT < 3.3 cm(3). The highest accuracy was found for VNACT, with 55.1% sensitivity given 100% specificity. The volume regression after completed NACT and CRT (VCRT) 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.