Background: Cancer is common and radiotherapy is one well-established treatment for some solid tumours. HBO may improve the ability of radiotherapy to kill hypoxic cancer cells, so the administration of radiotherapy while breathing HBO may result in a reduction in mortality and tumour recurrence.
Objectives: To assess the benefits and harms of radiotherapy while breathing HBO.
Search strategy: In November 2004 we searched The Cochrane Central Register of Controlled Trials (CENTRAL), (The Cochrane Library Issue 3), MEDLINE, EMBASE , CINAHL, DORCTHIM and reference lists of articles. Relevant journals were handsearched.
Selection criteria: Randomised and quasi-randomised studies comparing the outcome of malignant tumours following radiation therapy while breathing HBO versus air (with or without sham therapy).
Data collection and analysis: Three reviewers independently evaluated the quality of the relevant trials using the method of Schulz (Schulz 1995) and extracted the data from the included trials.
Main results: Nineteen trials contributed to this review (2286 patients: 1103 allocated to HBO and 1153 control). With HBO, there was a reduction in mortality for head and neck cancers at both one year and five years after therapy (Relative risk (RR) 0.83, P = 0.03, number needed to treat (NNT) = 11 and RR 0.82, P = 0.03, NNT = 5 respectively), as well as improved local tumour control at three months (RR with HBOT 0.58, P = 0.006, NNT = 7). The effect of HBO varied with different fractionation schemes. Local tumour recurrence was less likely with HBO at one year (head and neck, RR 0.66, P < 0.0001, NNT = 5), two years (uterine cervix RR 0.60, P = 0.04, NNT = 5) and five years (head and neck (RR 0.77, P = 0.01). Any advantage is achieved at the cost of some adverse effects. There was a significant increase in the rate of both severe radiation tissue injury (RR 2.35, P < 0.0001, (number needed to harm (NNH) = 8) and the chance of seizures during therapy (RR 6.76, P = 0.03, NNH 22) with HBO.
Authors' conclusions: There is some evidence that HBO improves local tumour control and mortality for cancers of the head and neck, and local tumour recurrence in cancers of the head and neck, and uterine cervix. These benefits may only occur with unusual fractionation schemes. HBO is associated with significant adverse effects including oxygen toxic seizures and severe tissue radiation injury. The methodological and reporting inadequacies of the primary studies included in this review demand a cautious interpretation. More research is needed for head and neck cancer, but is probably not justified for bladder cancer. There is little evidence available concerning malignancies at other anatomical sites on which to base a recommendation.