TUMOR RADIOSENSITIZATION BY HIGH-OXYGEN-CONTENT GASES - INFLUENCE OF THE CARBON-DIOXIDE CONTENT OF THE INSPIRED GAS ON PO2, MICROCIRCULATORY FUNCTION AND RADIOSENSITIVITY
Sa. Hill et al., TUMOR RADIOSENSITIZATION BY HIGH-OXYGEN-CONTENT GASES - INFLUENCE OF THE CARBON-DIOXIDE CONTENT OF THE INSPIRED GAS ON PO2, MICROCIRCULATORY FUNCTION AND RADIOSENSITIVITY, International journal of radiation oncology, biology, physics, 40(4), 1998, pp. 943-951
Citations number
54
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: To measure the effects of breathing high-oxygen-content gases
, with a CO2 fraction of between 0 and 10%, on tumor radiosensitivity,
blood flow and oxygenation. Methods and Materials: The murine sarcoma
F was used, implanted subcutaneously (s.c.) in syngeneic CBA mice. We
assessed the induced changes in tumour microregional blood flow and o
xygenation using laser Doppler flowmetry, and pO(2) histography, respe
ctively. Radiation response was determined using an in vivo-in vitro c
lonogenic assay 18-20 h post treatment. Results: The results show that
the level of radiosensitization achieved is dependent on both the CO2
content of the inspired gas and the duration of gas breathing. No rad
iosensitization was evident following inhalation of 90% O-2 + 10% CO2.
All other gases elicited radiosensitization; however, that achieved w
ith 100% O-2 disappeared at the extended preirradiation breathing time
of 45 min. At this time, radiosensitization was maintained for gases
containing 1%, 2.5%, or 5% CO2. Changes in oxygenation, as measured by
pO(2) electrodes, did indicate improved oxygenation status during inh
alation of the gases. However, the time-course and extent of the chang
es did not mirror accurately the changes in radiosensitization. All th
e gases with a CO2 content of 2.5% or greater induced a 10-20% reducti
on in microregional blood flow, with no change evident following inhal
ation of 100% O-2 or 99% O-2 + 1% CO2. Conclusions: The data imply tha
t the decreased radiosensitization seen at extended breathing times of
oxygen is unrelated to blood flow changes. The fact that radiosensiti
zation is seen with extended breathing times of gases containing 2.5%
and 5% CO2, despite blood flow decreases, is indicative of other overr
iding physiological changes, perhaps related to oxygen utilisation. Th
e studies overall indicate that, at least in the tumour investigated,
radiosensitization is not affected if the CO2 content of the inspired
gas is reduced from 5% to 2.5%. or even 1%. Further evaluation of the
radiosensitizing effects of such gas mixtures is now warranted. In add
ition, comparison with recent studies of other tumour types, where car
bogen has been shown to improve tumour blood flow, suggests that this
may be a tumour-specific phenomenon. Based on these data, further effo
rt is required to elucidate the physiological mechanisms that determin
e these blood flow changes. (C) 1998 Elsevier Science Inc.