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Determination of the optimum dose per fraction in fractionated radiotherapy when there is delayed onset of tumour repopulation during treatment

¹ Radiation Physics and Radiobiology, Hammersmith Hospitals NHS Trust/Imperial College Faculty of Medicine, Charing Cross Hospital, London W6 8RF and ² Clinical Oncology, Imperial College Faculty of Medicine, Hammersmith Hospital, London W12 0HS, UK

View larger version (17K): [in a new window]   Figure 1. The relationship between optimum dose per fraction and K factor (biological dose per day required to compensate for ongoing tumour cell repopulation). The cases for which the time after the start of treatment at which proliferation begins (Tdelay)=0 may be derived via Equation (8). Cases for which Tdelay is non-zero muct be derived using the re-iterative method discussed in this article.

View larger version (17K): [in a new window]   Figure 2. The relationship between tumour biologically effective dose (BED) and K factor (biological dose per day required to compensate for ongoing tumour cell repopulation).

View larger version (10K): [in a new window]   Figure 3. Schematic showing how the dose required for a given tumour cell kill increases with prolongation of treatment time. The rise in the curves is a direct result of the repopulation that occurs during treatment. The "dog-leg" pattern of change is assumed for the purpose of the calculations in this article. The more plausible "continuous" pattern of change is shown for comparison. Tdelay, the time after the start of treatment at which proliferation begins.