Results: As previously reported (ESTRO 2015) we unexpectedly observed late grade (G)3 and 4 mucosal ulcers in 1/7 and 3/7 DPBN-patients in DPP1, respectively, that healed spontaneously (n = 1), after surgical intervention (n = 2) and is still persisting (n = 1) at 42 months. In order to avoid G4 mucosal late toxicity (LT) the DPBN-DPP has been adapted in 2 steps (Fig. 1 ): DPP1 used a median dose prescription that can result in increased doses in a GTV with > 50% voxels of low-uptake. This

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... n dose prescription was abandoned in DPP2. In DPP3 the very-high dose region is limited to an absolute volume of 1.75 cc. In DPP2, 1/2 had G3 mucosal LT that healed spontaneously. In DPP3, 2/11 and