Bm. Fenton et al., SHOULD DIRECT MEASUREMENTS OF TUMOR OXYGENATION RELATE TO THE RADIOBIOLOGICAL HYPOXIC FRACTION OF A TUMOR, International journal of radiation oncology, biology, physics, 33(2), 1995, pp. 365-373
Citations number
41
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: Numerous previous studies have attempted to relate the radiob
iological hypoxic fraction (HF) to direct measures of tumor oxygenatio
n such as HbO(2) saturations, tumor pO(2) levels, or hypoxic cell labe
ling, Although correlations have been found within tumor lines, no ove
rall relationships were seen across tumor lines. The current objective
was to examine the effect on HF of changes in the fractions of the ox
ygenated and anoxic tumor cells that remain clonogenic. Methods and Ma
terials: A mathematical model was developed that relates the HF to dir
ect measures of tumor oxygenation, The primary assumptions were that:
(a) the tumor is divided into distinct compartments of either fully ox
ygenated or fully anoxic cells, and (b) the survival of the oxygenated
cells is negligible compared to that of the anoxic cells, Based on th
ese assumptions, the HF is plotted as a function of the fractions of c
lonogenic or nonclonogenic, and oxygenated or anoxic cells. Results: I
f all cells are clonogenic, then the HF equals the fraction of anoxic
cells, If a higher fraction of anoxic than oxygenated cells are nonclo
nogenic, then the HF will be overestimated by the fraction of the tumo
r measured to be anoxic using direct measuring techniques, If a higher
fraction of the oxygenated than anoxic cells are nonclonogenic, the H
F will be underestimated by the fraction of anoxic cells. Conclusion:
Correlations between the HF and direct measures of tumor oxygenation h
ave been described within tumor lines evaluated under different physio
logical condition, However, such relationships can be totally unpredic
table between different tumors if the fraction of the anoxic cells tha
t is clonogenic varies substantially, Clearly, if tumor anoxia cannot
be detected using direct measures, this is an accurate indication that
the tumor is well oxygenated, When tumor anoxia is present, however,
the conclusions are ambiguous, Even when a small fraction of the tumor
is measured as anoxic, direct measures of tumor oxygenation may not b
e representative of the HF if a substantial proportion of nonclonogeni
c cells is present.