Delineation of clinical target volume in nasopharyngeal carcinoma

Radiotherapy is the mainstay treatment modality for nasopharyngeal carcinoma (NPC). Intensity-modulated radiation therapy (IMRT), as the standard technique, achieves the purpose of improving target coverage and better sparing of normal tissue. Increased attention has been given to explore various strategies for deescalating treatment intensity. The optimization of clinical target volume (CTV) is one of the most active research areas being widely discussed. Although the International Guidelines for the delineating of CTV in NPC had provided important references for clinicians, there are marked variations in practice among different institutions. This article reviews the development of CTV delineation in non-metastatic NPC patients among centers, and compares the similarities and differences in CTV delineation of various current guidelines in the hope of providing insights for future investigation. This review aims to provide a comprehensive summary of the development and evolution of CTV delineation on primary tumor and lymph nodes for definitive radiotherapy in non-metastatic NPC through historical lens. We also compare the differences of CTV delineation ways. In addition, we look into the clinical and practical challenges of CTV delineation, hoping to provide direction for future research.