On the delineation of the gross tumor volume and clinical target volume for head and neck squamous cell carcinomas.

Gross tumor volume (GTV) and clinical target volume (CTV) delineation on planning computed tomography (pICT) for head and neck squamous cell carcinomas can be troublesome. We highlight the factors which can be crucial for the radiation oncologist in delineating GTV and CTV on pICT and provide some pratical solutions. Regarding GTV, uncertainties are correlated with transfer of information collected by physical examination and diagnostic radiology to pICT. Moreover, reproducibility of delineation can also be highly variable, particularly when diagnostic imaging quality and pICT quality are poor. Once the prescription has been made, clinical target volume identification on pICT is rarely straightforward. Whereas there are some data about the location of major lymph node stations of the neck, there are no reported guidelines on how to draw subclinical extention of primary head and neck tumors on pICT. Such volumes can be derived from those currently included in simulator films or from those addressed by the surgeon. Some examples are provided. A particular situation is represented by the adjuvant setting, when the primary tumor is removed (by surgery) or reduced (by chemotherapy). In conclusion, this paper shows some major problems associated with identification of GTV and CTV on pICT. Apart from selected cases, the use of pICT for target volume delineation (and thus for field shaping) for head and neck squamous cell carcinoma is still to be considered investigational.