Late effects are the result of damage to the vascular supply of tissues and perhaps of damage to the stem cells that maintain the tissues. Whereas each of these factors may have a different impact on early and late effects, each must be considered in the treatment plan. Simulation of the radiation treatment is carried out on so-called phantoms to maximize the delivery of radiation to the tumor volume and to minimize delivery to normal overlying or adjacent tissues. Raising or lowering the energy of radiation changes the distribution of radiation effects within the treatment volume. Advances in imaging, especially CT scanning, have improved treatment planning by permitting the radiation oncologist to visualize tumors in areas of anatomic complexity.
Radiation therapy is associated with unique benefits as well as important toxicities.
Radiation treatment exploits the fact that radiation damage is not uniform between malignant and normal tissues. In the treatment of lymphomas and seminomas, for example, the tumor tissue is more sensitive to radiation damage than are normal tissues. On the other hand, such differences in radiation sensitivity do not extend to most carcinomas. In certain anatomic areas, such as the mediastinum, radiation may be the only feasible local method of treatment because surgery in these regions may be associated with unacceptable morbidity. Radiation may also be the only feasible local modality if tumor involvement is extensive, as may be the case in chest wall recurrences of breast cancer, because no other local modality can encompass the involved area.