External beam radiotherapy and bone metastases

Bone is a common site for the development of metastatic disease from solid tumors. The most common primary tumor sites that spread to bone are breast, prostate, lung, thyroid, kidney and bone marrow (multiple myeloma), though other primary tumor sites can give rise to osseous metastasis as well. Optimal management requires a collaborative approach, often with input from physicians of various disciplines. Both symptomatic and asymptomatic bone lesions can be palliated with radiation (1). Symptoms of bone metastasis can occur early in a patient’s metastatic course and include localized pain and/or pathologic fracture, functional deficits due to compression of peripheral nerves, nerve roots, or the spinal cord (2,3). Osseous metastasis cause pain directly, through local invasion, and indirectly through alteration of the remodeling activity of osteoblasts and osteoclasts. Pain can be caused by the release of chemical mediators, increased pressure due to tumor, microfractures and stretching of the periosteum (4). Bone metastasis can weaken the bone such that even minor activity such as coughing or sneezing can result in a pathologic fracture. Vertebral bodies can become so compromised that they lose height, which can cause muscle spasms as the muscles struggle to maintain spinal integrity. Nerve involvement can present as radicular or referred pain. Patients perceive pain in various terms, including “burning”, “sharp”, “aching”, and “cramping”. Systemic manifestations of osseous disease include hypercalcemia, fatigue, and anorexia. Treatment of asymptomatic metastasis can prevent pathologic fracture or neurologic compromise from impending spinal cord compression. Asymptomatic lesions of the acetabulum are frequently the targets of radiation therapy as surgical options for acetabular fractures are limited and may result in the patient being unable to bear weight for the remainder of his lifetime