BACKGROUND: Gaps are a common feature of clinical radiotherapy. Only little information is available about the influence of the position of a gap on tumor response. MATERIAL AND METHODS: In a rodent tumor model (rhabdomyosarcoma R1H of the rat) three split-course schedules were carried out by inserting a 2-week gap either after the 1st, the 3rd, or the 5th week into a standard schedule of 30 fractions in 6 weeks. For comparison a standard and an accelerated treatment were carried out. RESULT AND CONCLUSION: The position of the gap was found to have a significant influence on the tumor response (p = 0.018).
