Tumour size: a factor influencing the isoeffect analysis of tumour response to combined modalities.

Isoeffect analysis of complete dose response curves can be used to study the interaction of agents in combined modality protocols. When such an analysis is applied to data from in vivo tumour model systems, the effects of the agents on factors such as tumour vasculature, growth or reoxygenation pattern also need to be considered. In this study the change in tumour size, which can occur during a long time-interval between agents, was used as an example of a factor which may influence the position of data points on an isoeffect plot.

The effect of chronic reductions in the arterial partial pressure of oxygen on the radiation response of an experimental tumour.

A previous study by the same authors has reported the effect of acute reductions in the arterial partial pressure of oxygen (PaO2) on tumour response to radiation. The results have been extended in the present paper to investigate tumour response to radiation in animals in which the PaO2 is chronically reduced. The purpose of these experiments was to simulate the condition of cancer patients undergoing radiotherapy in the presence of chronically low PaO2 values as might be expected in patients with chronic respiratory disease.

The relationship between mouse arterial partial pressure of oxygen (PaO2) and the effectiveness of localized tumour irradiation.

The effectiveness of localized X-irradiation on the transplantable KHT sarcoma was investigated while the host mice breathed gas mixtures ranging from 5% O2 : 95% N2 to 100% O2. Subcutaneous tumours in the flank of C3H mice anaesthetized with Nembutal (sodium pentobarbitol), Valium (diazepam), or urethane, were irradiated with doses of 1,500 or 2,500 rads and the delay in days for the tumours to grow from 4 to 10 mm in diameter was determined. Measurements of the arterial partial pressure of oxygen (PaO2) were made under conditions identical to the irradiation experiments.