Guidelines for Complications of Cancer Treatment Vol VIII Part B

Pathophysiological Aspects:The functional unit of the lung is the pulmonary lobule. It liesentirely within the lung parenchyma and consists of the terminalbronchiole and that segment of the respiratory parenchymathat it serves. Reactive oxygen species generated by radiationare toxic to parenchymal cells. The most radiosensitive subunitof the lung is the alveolar/capillary complex and injury to thiscauses diffuse alveolar damage. This initiates a cascade ofmolecular events, creating a self-sustaining cycle ofinflammation and chronic oxidative stress. The culminatingevent is replacement of normal lung parenchyma by fibrotictissue. The range of respiratory compromise can extend fromacute lethal events to varied degrees of chronic pulmonarydecompensation which manifest at years after the initial cancertherapy. When the entire lung is irradiated with a single largefraction as in total body irradiation, there is a steep dose–response relationship starting at 8.2 Gy. Conversely, treatmentwith multiple daily fractions to a whole lung dose of 17.5 Gyappears to be well tolerated.Factors influencing pulmonary toxicityPatient Related Factors Treatment Related factorsPerformance status Volume of lung irradiated, andtheHistory of smoking Dose received by the lungChronic Obstructive Percentage of total normal lungPulmonary Disease volume exceeding the dose of20GyPulmonary function tests Mean lung dose(FEV1, DCLO)Tumour siteFractionation of radiotherapyUse of chemotherapy315