Partial irradiation of the lung

Many factors like fractionation, overall treatment time, and patient specific aspects are important when studying and quantifying the effects of partial lung irradiation. The local reactions of lung tissue to irradiation are described with regard to the dose-volume effect. Different models that are used to predict the incidence of radiation pneumonitis and the influence of irradiation on the overall lung function are discussed. The easy-to-calculate mean lung dose (MLD) and the volume irradiated to 20 Gy (V20) can both be used to predict the incidence of radiation pneumonitis. These parameters represent 2 extremes in underlying local dose-effect relations for radiation pneumonitis. However, clinically applied treatment plans show a high correlation between the V20 and the MLD, so that the decision for the "best" underlying local dose-effect relation should be based on the analysis of additional patient data. Dose-escalation studies and multi-center co-operation will create more possibilities to investigate all confounding factors concerning lung irradiation.