To ensure the maximum effect of oncological treatment, in the case of lung cancer, irradiation of the tumor with high doses of radiation is essential. However, this goal is often not achieved with conventional irradiation due to possible damage (toxicity) to the surrounding healthy tissues. The most serious manifestations of radiotherapy toxicity for non-small cell lung cancer are radiation pneumonitis, esophagitis and cardiac toxicity.
Clinically significant radiation pneumonitis develops in 5-50% patients treated with pulmonary tumors. Another quite big group of patients has subclinical signs of radiation pulmonary damage (determinable in lung function tests, radiologic changes). Pneumonitis is not so common (10-25%) after stereotactic radiotherapy. However, this procedure is associated with higher risk of bronchial stenosis after irradiation of perihilous/central tumors.
Esophagitis incidence increases together with the “aggressiveness” of the radiotherapy. Grade 3 and higher acute esophagitis develops in about 1% patients treated with standard fractionation. In concomitant chemotherapy administration, the incidence reaches the range of 6-24% (gemcitabine regimens up to 49% patients), about 20% in hyperfractionated radiotherapy. Patients older than 70 years have higher risk. The recommended dosage limits have not been precisely determined, data from clinical trials are not consistent. For example Radiation Therapy Oncology Group (RTOG) 0617 trial recommends medium dose < 34 Gy. Other stated limits reach the level of V50 ≤ 50%, V70 ≤ 40%.
Acute toxicity has the character of pericarditis. Usually, it is a temporary affection (however, up to 20% cases may progress to chronic stage). Late toxicity is of higher severity (it develops months or years after radiotherapy), manifesting as heart ischemia, myocardial infarction or congestive heart failure. The relative risk of ischemic complications is 1.3-3.5. The V25 ≤ 10% parameter (volume of myocardium irradiated with the dose of 25 Gy in standard fractionation) is associated with less than 1% cardiac death risk within 15 years of radiotherapy completion.
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