The ability of hyperbaric
oxygen (HBO) treatment to modulate the response of a rodent
fibrosarcoma to interstitial
photodynamic therapy (
PDT) using 630 nm light and intravenous
polyhaematoporphyrin (PHP) was examined. Application of HBO for 30 min immediately prior to
PDT resulted in a light dose-dependent increase in tumour growth retardation, maximum effect (+227%) being observed with 100J light, and no enhancement being seen at or above 400J. Application of HBO during or immediately after
PDT had no effect on response. Reducing the interval between giving PHP and administering light from the usual 48 h to just 1 h increased the efficacy of
PDT even in the absence of HBO pre-treatment. Under these circumstances, application of HBO did not realise any further increase in tumour response at any light dose. Our findings suggest that manipulation of tumour oxygenation may be able to improve the outcome of
PDT under some circumstances, but that careful consideration of other treatment variables, such as light dose and
drug-to-light interval, may provide similar, more easily achievable, improvements in efficacy.