Effect of carbogen on tumour oxygenation and 32P-colloid interstitial irradiation response

Background: Interstitial irradiation therapy using radionuclides is a slow and continual process in which the effect is exerted gradually, thus improvement of the hypoxic status of the tumor will also take a long time. It has been known that carbogen delivery of 5-15 min increases tumor oxygenation. However, the long-term effect of carbogen breathing on hypoxic cells has not yet been determined, and little is know about the effect of carbogen breathing for sensitization to interstitial irradiation therapy. Material/Methods: ^99mTc-HL91(^99mTc 4,9-diaza-3,3,10,10-tetramethyldodecan-2, 1-dione dioxime) hypoxic imaging was performed in 10 mice bearing sarcoma 180 (S180) before and after 2 h carbogen breathing. Radioactivity ratios of tumor to contralateral limbs (T/L) of the 2 images were calculated and compared. Mice bearing S180 were subjected to long-term carbogen breathing (2 h/day for 24 days), and were treated with or without ³²P-colloid. Tumor growth rate was observed in the S180-bearing mice. Results: T/L of ^99mTc- HL91 uptake before and after carbogen breathing was 1.872±0.391 and 1.354±0.189, respectively (t=4.476, P<0.01). In mice in the ³²P-treated air breathing group and ³²P-treated carbogen breathing group, tumor growth rate did not differ on day 12 after ³²P-colloid treatment, and on day 24 the tumor volume was 2.728±0.469 and 2.237±0.603 cm³ (t=2.128, P<0.05), respectively, with tumor mass being 2.437±0.447 and 1.965±0.538 g (t=2.134, P<0.05), respectively. Conclusions: Long-term carbogen breathing can increase tumor oxygenation and continual carbogen breathing is necessary for enhancing the therapeutic effect of ³²P-colloid interstitial irradiation.