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By extrapolation to zero time, the initial and final slopes of data sets which probably demonstrate the existence of accelerated repopulation during radiotherapy can be used to estimate the lower limits of the initial tumour hypoxic fraction. The slow repopulation phase (initial slope) is assumed to reflect treatment in mixed oxic and hypoxic conditions and the later fast repopulation (final slope) phase that of a well-oxygenated cell population. The method assumes that accelerated repopulation in tumours results from an improvement in oxygen status during radiotherapy, but quantitative knowledge of repopulation factors is not required in the calculations. Using the data of (a) Withers et al. (for head and neck squamous cell cancer) and (b) Maciejewski and Majewski (for bladder cancer), the lower (limits of initial hypoxic fraction appear to be between 10 and 52%, the exact values depending on the value assumed for the oxygen-enhancement ratio (OER) of the hypoxic compartment. The analysis also suggests that the half-life of effective tumour reoxygenation is probably less than 5 days.

Original publication

DOI

10.1080/028418698429568

Type

Journal article

Journal

Acta Oncologica

Publication Date

15/07/1998

Volume

37

Pages

263 - 268