Spatial oxygenation profiles in tumors during normo- and hyperbaric hyperoxia

Area of Science:

• Oncology
• Radiotherapy
• Biomedical Engineering

Background:

• Tumor hypoxia limits radiosensitivity, making it a target for cancer treatment.
• Inspiratory hyperoxia is used to reduce tumor hypoxia, but intratumoral oxygenation heterogeneity during this treatment is poorly understood.
• This study investigates local hypoxia presence and spatial pO2 distribution during normobaric and hyperbaric hyperoxia, with and without CO2.

Purpose of the Study:

• To determine if local tumor hypoxia persists during normobaric and hyperbaric inspiratory hyperoxia.
• To assess the impact of CO2 addition to inspiratory gas on spatial pO2 distribution within tumors.
• To analyze the heterogeneity of intratumoral oxygenation under different hyperoxia conditions.

Main Methods:

• Experimental DS-sarcomas in rats were used to assess tumor oxygenation.
• Polarographic needle electrodes measured pO2 at 1 and 2 atm environmental pressure.
• Measurements were taken during pure O2 or carbogen (95% O2 + 5% CO2) breathing, with up to 320 measurements per tumor in a grid pattern.

Main Results:

• Tumor oxygenation exhibited significant heterogeneity with adjacent hypoxic and oxygenated regions.
• Normobaric hyperoxia still showed large, confluent hypoxic regions.
• Hyperbaric hyperoxia (2 atm) revealed only small hypoxic regions, with CO2 having no significant impact at this pressure.
• CO2 addition improved tumor oxygenation at 1 atm, especially in larger tumors.

Conclusions:

• Local hypoxic regions remain detectable even under hyperbaric hyperoxia, despite a 100-fold increase in average pO2.
• Increasing environmental pressure disproportionally improves tumor oxygenation patterns.
• The spatial distribution of oxygenation within tumors is significantly affected by hyperbaric conditions.