Target Volume Definition in Non-Small Cell Lung Cancer

Proper target volume delineation is a crucial stage of treatment planning, so any error introduced in this process is a systematic error and cannot be quantified and/or detected by modern treatment technologies, unlike other sources of geometrical uncertainties. All steps of target definition should be standardized. In non-small cell lung cancer radiotherapy, there are specific problems related to the definition of all three consecutive target volumes recommended by ICRU: gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV). In GTV delineation, the proper imaging, e.g., standardized way of the use of CT and PET-CT, and continuous radiological training of radiation oncologists are emphasized. For CTV, we still lack robust data on the margin which is necessary to expand around GTV of the tumor and pathologic lymph nodes to adequately account for microscopic spread. Additionally, elective nodal irradiation is still a source of controversies. For PTV definition, major increase in technologies is involved. It leads in some cases to improvement of the tumor coverage and sparing of organs at risk, but as this process is expensive and time consuming, it might not be always beneficial.