Voxel-by-voxel NTCP modelling of severe radiation-induced lung injury after image-guided, IMRT for lung tumors.

Lung cancer is one of the most common type of cancer around the world with over 1.5 million deaths every year. In particular, non-small cell lung cancer (NSCLC) is the most frequent and accounts for about 85% of cases in European countries. In the treatment of lung tumors, radiation therapy (RT) plays an important role in treating NSCLC, and several studies have reported promising results, especially for patients with early stage NSCLC, who are unfit for surgery or who are medically operable but refused surgery. The most recent technological advances in RT such as stereotactic body radiotherapy (SBRT), image-guided radiotherapy (IGRT) and highly conformal techniques such as intensity-modulated radiotherapy (IMRT), allow to irradiate small volumes to high doses with minimal exposure of the surrounding healthy tissues, increase the loco-regional control and reduce the risk and severity of late side effects of RT. These factors have a significant impact on the overall survival and progression-free survival. The irradiation of the lung, however, can lead to complications such as radiological radiation-induced pulmonary injury (RRLI), which consists in the appearance of an increase in lung tissue density and opacity, seen on the follow-up chest computed tomography (CT). The appearing of RRLI after RT of lung cancer is very common. It occurs typically in 62% of patients within six months after treatment (acute effects) and 91% thereafter (late effects). However, only a small number of patients develop clinical symptoms. Although RRLI is mostly asymptomatic, it can also lead to a progressive and irreversible decline in the pulmonary function. The prediction of occurrence of side effects after RT is crucial for optimization and evaluation of RT treatment plans and the long-term quality of patients life. Normal tissue complication probability (NTCP) models describe the probability that a given dose distribution of a treatment will result in some quantifiable and unfavourable side effects to a tissue or organ. For ...