When using conventional irradiation, the patient is exposed to excess radiation to the healthy tissues. This poses a risk of late and very late toxicity. This means that consequences of unwanted irradiation of healthy tissues and organs are often manifested in the future, long after the treatment is over, including heart or lung damage or secondary tumors.
Other frequent side effects are esophageal damage leading to swallowing difficulties, and heart damage possibly impairing cardiac function.
Not even modern conventional photon therapy allows for further significant reductions in doses to risk organs. It does not allow dose reduction to the heart muscle, valves and coronary arteries, and can cause valvular defects, ischemic heart disease and arrhythmias.
Conventional photon therapy in combination with chemotherapy would also affect the heart, which is the cause of cardiopulmonary problems. Dose reduction is of utmost importance in this case.
Spinal cord irradiation combined with previous chemotherapy leads to myelopathy, even when adhering to tolerance doses. It may further result in higher radiation exposure of the mammary glands, subsequently increasing the risk of secondary malignancies.
Even modern photon irradiation techniques (IMRT, including dynamic IMRT) may be associated with higher irradiation of healthy tissues, which may be insignificant for the development of acute toxicity but not negligible for the risk of late toxicity. Current conventional photon radiation has already reached its physical limits. However, proton therapy is available as a solution to reduce doses to high-risk organs.