MR-guided simultaneous integrated boost in preoperative radiotherapy of locally advanced rectal cancer following neoadjuvant chemotherapy

PurposeTo evaluate a simultaneous integrated boost (SIB) strategy in preoperative radiotherapy of rectal cancer patients following neoadjuvant chemotherapy using pre- and post-chemotherapy tumor volumes assessed by MRI.Materials and methodsTen patients with locally advanced rectal cancer, receiving chemotherapy prior to radiotherapy, were included in this study. Pre- and post-chemotherapy MR tumor images were co-registered with CT images for IMRT planning. Three planning target volumes were defined: PTVrisk, PTVpre_chemo and PTVpost_chemo. For SIB, prescribed mean doses to the PTVs were 46, 50 and 58 Gy, respectively, given in 25 fractions. Organs at risk (OARs) were bladder and intestine. The novel three-volume SIB strategy was compared to a conventional two-volume SIB plan, in which PTVpost_chemo was ignored, using dose–volume histograms (DVHs) and the generalized equivalent uniform dose (gEUD).ResultsAll patients showed tumor shrinkage following chemotherapy. For the novel SIB, population-based mean doses given to PTVrisk, PTVpre_chemo and PTVpost_chemo were 46.8 ± 0.3, 50.6 ± 0.4 and 58.1 ± 0.4 Gy, respectively. DVHs and gEUDs for PTVrisk, PTVpre_chemo, bladder and intestine revealed minimal differences between the two SIB strategies.ConclusionsTumor volume reduction for rectal cancer patients following neoadjuvant chemotherapy allows for increased tumor dose using a SIB strategy without increased OAR toxicity.