Combining radiation therapy with other treatment modalities.

Combining treatment modalities is indicated when single modality treatment does not result in adequate tumor control, or if the cosmetic or functional outcome of single modality treatment is less than desirable. The combination of surgery and radiation has proven useful in the treatment of both human and veterinary patients. Surgery can be used to remove large, bulky tumors whereas radiation therapy eliminates the subclinical disease adjacent to the tumor mass that invades important normal tissue structures. If properly combined, the result should be better tumor control combined with a better functional and cosmetic outcome. Radiation therapy can be administered preoperatively, postoperatively, and intraoperatively, depending on a variety of factors. Radiation therapy combined with hyperthermia has a strong scientific rationale. Hyperthermia is particularly effective against some cells, such as those in late S-phase, that are resistant to radiation therapy. Nutrient-deprived cells and cells with low pH are also very sensitive to hyperthermia, and these may reflect areas in a tumor where hypoxia may be present. Therapeutic gain has been shown in randomized clinical trials combining radiation therapy and hyperthermia in tumor bearing dogs. However, the disadvantage of hyperthermia for both human and veterinary tumors remains the inability to adequately maintain uniform temperatures to the tumors. Chemotherapy is an important adjuvant to radiation therapy for the control of distant tumor spread. The scientific rationale for combining chemotherapy with radiation therapy for local control is less clear, and is complex because of a variety of factors.