Combination of HBO with radiotherapy is considered to be useful for the following reasons:
- It allows a more uniform kill by improving the oxygenation, and therefore the radiosensitivity, at the cellular level.
- It is useful as an adjunct to surgical repair after radiation.
HBO is considered to be the most effective method for counteracting tumor hypoxia for enhancing the effect of radiotherapy on cancer). The advantages of HBO combined with radiotherapy are:
- HBO is also a useful therapy for radiation-induced necrosis of normal tissues.
- In a controlled study of patients with or without HBO, the survival has shown to be higher in the HBO control group. The greatest advantage was seen in the less advanced tumors).
- In experimental bladder tumor, tissue oxygen tension has been shown to be higher in the bladder trigone region (Nakada 1988). HBO was shown to enhance the effect of combined chemotherapy and radiotherapy in this model (Akiya et al 1988).
Cancer Therapy Committee (CTC)
Machin et al (1997) have reviewed the survival outcome from the randomized Phase III trials in solid tumors published on behalf of, or in collaboration with, the
of the British Medical Research Council over a 30-year period to 31 December 1995. In all, 32 trials, involving over 5000 deaths in more than 8000 patients, have been published. Tumor types have included bladder, bone, brain, cervix, colon and rectum, head and neck, kidney, lung, ovary, prostate and skin. The MRC trials have made an impact on both clinical practice and research activities. Trials of HBO have defined the biological activity of this approach, and the appropriate dose of radiotherapy in patients with brain tumors has been found.
There is considerable evidence for the presence of hypoxia in human tumors.
Vascular insufficiency has been demonstrated on histopathology of the tumors, direct oxygen measurements, and mapping of hypoxic areas by imaging techniques. It appears that hypoxia is probably responsible for failure to cure some tumors such as squamous cell carcinoma, but even within tumors of the same stage and type, hypoxia does not occur to the same extent. Response to modifying agents also depends upon whether hypoxia is acute or chronic. New methods to detect hypoxic tumor cells (hypoxic cell stains) are being developed. The future prospects for the control of these tumors where hypoxia is a problem appear to be good.
Of the various adjuvants to radiotherapy, HBO appears to be the best (Henk 1981). It can be combined with other radiation enhancers. The effect of HBO in enhancing radiosensitivity is most pronounced in head and neck tumors.