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Updated: Jun 19, 2026
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Published on: February 12, 2022
MR-guided simultaneous integrated boost in preoperative radiotherapy of locally advanced rectal cancer following
Therese Seierstad1, Knut Håkon Hole, Erik Saelen
1Department of Radiation Biology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway. Therese.Seierstad@rr-research.no
Purpose:
To 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 Methods:
Ten 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: PTV(risk), PTV(pre_chemo) and PTV(post_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 PTV(post_chemo) was ignored, using dose-volume histograms (DVHs) and the generalized equivalent uniform dose (gEUD).
Results:
All patients showed tumor shrinkage following chemotherapy. For the novel SIB, population-based mean doses given to PTV(risk), PTV(pre_chemo) and PTV(post_chemo) were 46.8+/-0.3, 50.6+/-0.4 and 58.1+/-0.4 Gy, respectively. DVHs and gEUDs for PTV(risk), PTV(pre_chemo), bladder and intestine revealed minimal differences between the two SIB strategies.
Conclusions:
Tumor volume reduction for rectal cancer patients following neoadjuvant chemotherapy allows for increased tumor dose using a SIB strategy without increased OAR toxicity.
