Cardioprotective radiotherapy: the circadian way.

Radiotherapy (RT) has been established to improve both local control as well as overall survival rates in breast cancer. However, RT especially in left-sided breast cancer also irradiates a portion of the heart. Radiation associated toxicity to the heart assumes significance because of improval in survival of breast cancer patients. A circadian pattern has been reported in the myocardial oxygen demand and myocardial ischaemia with the cardiac tissue being more susceptible to injury between 6 am and noon. Radiation damages blood vessels of all sizes causing an increase in capillary wall permeability and dilatation of vessels leading to the characteristic radiation erythema followed by an inflammatory cell infiltrate. Coronary artery spasm may be the reason behind some cases of sudden death occurring in patients after radiation therapy. Endothelial behaviour also has a circadian variation and vasodilation is significantly attenuated in the morning. Critical coronary artery disease occurs 10-15 years after radiotherapy. Radiation in the morning hours may be one of the associated risk factor. The application of chrono-therapeutics with radiation therapy in carcinoma breast and in other chest wall irradiation, could possibly decrease the radiation associated cardiac toxicity.