The response of a rodent fibrosarcoma to photodynamic therapy (PDT), radiotherapy (RT) or combined PDT and RT was examined. PDT used intravenous polyhaematoporphyrin (PHP) and interstitial illumination with 630 nm light (300 or 400J). RT was given as an external beam of gamma-rays (15, 20 or 25 Gy). Both PDT and RT induced a significant delay in tumour growth when applied alone. PHP given alone, without subsequent illumination, did not alter the response of the tumour to RT. The effect of combining PDT and RT was dependent on the dose of light administered, but not, in most cases, on either the radiation dose or the sequence in which the two treatments were given. Using 300J of light, all combined treatments produced additive tumour growth delays. In contrast, sub-additive tumour responses were observed following most combined treatments using 400J of light.

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