Synergistic Combination of Hyperoxygenation and Radiotherapy by Repeated Assessments of Tumor pO[sub.2] with EPR Oximetry

• Published in: Journal of radiation research Vol. 52; no. 5; p. 568
• Main Authors: Hou, Huagang, Dong, Ruhong, Lariviere, Jean P, Mupparaju, Sriram P, Swartz, Harold M, Khan, Nadeem
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01-09-2011
• Subjects: Analysis; Radiotherapy; Tumors
• ISSN: 0449-3060
• DOI: 10.1269/jrr.11028

The effect of hyperoxygenation with carbogen (95% O[sub.2] + 5% CO[sub.2]) inhalation on RIF-1 tumor pO[sub.2]and its consequence on growth inhibition with fractionated radiotherapy is reported. The temporal changes in the tumor pO[sub.2] were assessed by in vivo Electron Paramagnetic Resonance (EPR) oximetry in mice breathing 30% O[sub.2] or carbogen and the tumors were irradiated with 4 Gy/day for 5 consecutive days; a protocol that emulates the clinical application of carbogen. The RIF-1 tumors were hypoxic with a tissue pO[sub.2] of 5-9 mmHg. Carbogen (CB) breathing significantly increased tumor pO[sub.2], with a maximum increase at 22.9-31.2 min on days 1-5, however, the magnitude of increase in pO[sub.2] declined on day 5. Radiotherapy during carbogen inhalation (CB/RT) resulted in a significant tumor growth inhibition from day 3 to day 6 as compared to 30%O[sub.2]/RT and carbogen (CB/Sham RT) groups. The results provide unambiguous quantitative information on the effect of carbogen inhalation on tumor pO[sub.2] over the course of 5 days. Tumor growth inhibition in the CB/RT group confirms that the tumor oxygenation with carbogen was radiobiologically significant. Repeated tumor pO[sub.2] measurements by EPR oximetry can provide temporal information that could be used to improve therapeutic outcomes by scheduling doses at times of improved tumor oxygenation. Keywords: Carbogen, EPR oximetry, Irradiation, Tumor oxygenation