Scientific and clinical aspects of radiotherapy in the relief of bone pain.

Radiotherapy is highly effective in relieving metastatic bone pain. The mechanism of action remains unclear, and tumour shrinkage may be relatively unimportant in producing analgesia. Various techniques of localized external beam therapy are in use with no consistent advantage seen for either high doses or multiple fractions. For scattered painful metastases, wide-field hemibody irradiation or the systemic administration of radioisotopes are effective but may be associated with greater toxicity than localized irradiation.