Radiobiological basis and clinical results of the simultaneous integrated boost (SIB) in intensity modulated radiotherapy (IMRT) for head and neck cancer: A review.

The simultaneous integrated boost (SIB)-IMRT technique allows the simultaneous delivery of different dose levels to different target volumes within a single treatment fraction. The most significant aspect associated with SIB-IMRT is related to the fractionation strategy, concerning two time-dose parameters: (1) the shortening of the overall treatment time (OTT); (2) the increase of fraction size (FS) to the boost volume. The SIB-IMRT technique represents, therefore, a new way to investigate the accelerated fractionation in definitive treatment of head and neck (H&N) cancers. The aims of this paper are the following: (1) to briefly review the influence of OTT and FS on H&N tumors and on acutely and late responding normal tissues; (2) to review the results of clinical studies of accelerated radiotherapy not employing IMRT in H&N cancer; (3) to review the clinical experiences of the SIB-IMRT technique and to compare the different SIB regimes in terms of radiobiological efficacy.