The simultaneous integrated boost with proton beams in head and neck patients.

The potential benefit of the simultaneous integrated boost (SIB) concept in proton therapy was investigated in a planning study. The proposed fractionation strategy consisted of a SIB treatment following a first phase of conventional fractionation to the elective volume (named SEQ/SIB). The novel method was compared to a conventional sequential fractionation and to a full SIB approach. Treatment plans were designed for five patients on the proton planning system developed for spot scanning at the Paul Scherrer Institute of Villigen (CH). Three to five beams were applied for all plans and fractionations. All effective dose distributions were corrected using biological models to take into account repopulation and time at repopulation onset. Corrected and uncorrected plans were compared on the basis of dosimetry criteria and dose-volume histograms. The results showed a dosimetric advantage for the SEQ/SIB approach in terms of target coverage, without significant disadvantages for risk structures and healthy tissue. Considering the high logistic impact and the limited availability of radiation facilities, the clinical exploitation of accelerated SIB treatment with protons appears promising.