In general, the larger the daily dose of radiation, the lower the total dose that can be administered because of limits to normal tissue tolerance. Proportionately more tumor cells are killed when the daily radiation dose is larger. A balance is required between the killing of tumor cells and the adverse radiation effects on normal tissues, which are largely a function of the daily dose. A number of different schedules have been developed that take into account specific tumor characteristics and the tolerance of normal tissues. The literature is divided regarding the optimal radiation schedule to achieve tumor regression (Hall, 1993; Thames, Withers, Peters, et al., 1982) and disease palliation (Price, Hoskin, Easton, et al., 1986) at either primary or metastatic sites. Generally, however, radiation treatment is planned in relation to clinical status.
The toxicity of radiation is determined by the structures included within the radiation portal, the dose per fraction, the total dose, and the radiation sensitivity of the tissues involved. The desired dosage of radiation should be administered in the fewest fractions possible to promote patient comfort during and after treatment. Radiation side effects are restricted to the radiation portal and can be classified as either acute, occurring during or immediately after the course of radiation therapy, or late, occurring months to years later. Acute radiation effects are more prominent with radiation schedules that deliver high total doses of radiation with small daily fractions; they generally begin at the end of the second week of therapy (Hall, 1993). Acute radiation effects, occurring primarily at skin and mucosal surfaces, usually consist of an inflammatory response such as skin erythema or pigmentation, or as mucositis. Acute reactions, however, are generally mild during palliative therapy schedules, which deliver high daily radiation doses over 1 to 2 weeks. Late radiation effects may arise without any preceding acute reactions. Fibrosis is the most common type of late radiation injury and can be observed in many types of tissue, including skin. Late effects are most prominent in tissues with limited regenerative capacity such as brain, peripheral nerves, and lungs. Because of the limited duration of patient survival, however, late effects are seldom seen after palliative radiotherapy.
NONPHARMACOLOGIC INTERVENTIONS: INVASIVE THERAPIES
Introduction (Invasive nonpharmacologic interventions)
Pain Relief with Localized Radiation Therapy
Wide-Field Radiation Therapy
Plexopathy
Other Therapeutic Applications
Nerve Blocks
Catheter Placement for Drug Delivery
Index