The evaluation of lung doses for radiation pneumonia risk in stereotactic body radiotherapy: A comparison of intensity modulated radiotherapy, intensity modulated arc therapy, cyberknife and helical tomotherapy INTRODUCTIONNon-small cell lung cancer (NSCLC) covers 75 -80% of all lung cancer patients. Approximately 15-20% of patients are localized and early stage. Generally, the 5-year survival rate is 60-70% when surgical treatment is performed in these patients. However, a significant proportion of patients with NSCLC are unsuitable for surgery because of the difficulties of lung surgery. In this case, radiotherapy is an important option, especially for patients without distant metastasis. In conventional radiotherapy, the probability of tumor control is 50% while its