Simultaneous Versus Sequential IMRT Boost in the Era of Treatment De-Escalation of Head and Neck Cancers

Radiation therapy is a central component of the definitive and postoperative management for head and neck cancers (HNC), with intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) now standard. Within these techniques, two principal boost strategies are used: simultaneous integrated boost (SIB) and sequential boost (SEQ). Although both are guideline-supported, they differ in planning logistics, treatment delivery, potential radiobiologic effects, adaptability to anatomic change, and potential toxicity profiles. In this narrative review, we summarize the key technical, dosimetric, and radiobiologic differences between SIB and SEQ and synthesize the available comparative clinical data, with a focus on their roles in contemporary dose de-escalation strategies. SIB allows for differential dosing within a single plan and potentially shorter overall treatment time but typically delivers higher biologically effective doses (BED) to elective nodal regions. SEQ requires two plans but offers greater flexibility for adaptive replanning, facilitates a lower BED to elective nodal volumes, and may allow for partial normal tissue recovery during the boost phase. Comparative studies, including retrospective series, randomized trials, and a meta-analysis, have not demonstrated consistent differences between SIB and SEQ in survival or local control, with mixed findings regarding toxicity. In the context of de-escalation, multiple prospective studies have successfully used SEQ to reduce elective nodal dose with low rates of elective nodal failure, while recent data suggest that SIB-based elective dose reduction may also be feasible in select settings. Overall, both SIB and SEQ are effective boost strategies in HNC radiotherapy. While practice is often driven by institutional workflow and clinician preference, emerging evidence suggests potential advantages of SEQ for elective nodal dose de-escalation. Further prospective studies are needed to better define the relative impacts of SIB and SEQ on toxicity and tumor control.