Less is more: level IB-sparing radiation therapy in nasopharyngeal cancer.

Abstract

pharynx. There are three pathological subtypes of NPC: keratinizing squamous, non-keratinizing, and basal squamous. Overall, NPC accounts for approximately 0.7% of all cancers worldwide [1]. The incidence of NPC varies significantly with geographic location, with the highest incidence in Southeast Asia and North Africa. According to an annual report on cancer statistics in Korea, the incidence of NPC is approximately 0.2% of all cancer cases [2]. In 2019, 416 new cases of NPC were detected in Korea. Radiotherapy (RT), either alone or in combination with chemotherapy, is the standard treatment for localized NPC. RT targets the gross tumor volume (GTV) of the primary tumor, metastatic lymph nodes (LN), and risk areas, considering the tumor spread patterns. Primary tumors of the nasopharynx tend to invade the surrounding soft tissues and bones, and spread along several foramina of the skull base. Cervical LN metastasis is widespread, with 60%–90% of patients present with LN metastasis at diagnosis [3]. The pattern of cervical LN metastasis in NPC is predictable and ordered. Skip metastasis is rare, with a risk of 0.5% to 2.7% [4,5]. Level II and lateral retropharyngeal LNs are the most commonly involved areas, followed by levels III, VA, and IV. As the nasopharynx is a midline structure, the efferents of lymphatics draining the central location often reach lymph nodes on both sides, resulting in bilateral lymph node metastases in the neck. This is particularly common in NPC, affecting up to 50% of patients. Traditionally, radiation targets routinely included the primary tumor, retropharyngeal area, and whole neck bilaterally. The Radiation Therapy Oncology Group 0225 protocol [6] and an institution in Hong Kong [7] routinely include bilateral level I to V LNs. This was based on the pattern of LN metastases, the radiation field of the conventional two-dimensional RT technique, and the use of less accurate imaging. In contrast, with more advanced imaging methods available, such as magnetic resonance imaging (MRI) and positron emission tomography/computed tomography, LN metastases more easily and accurately detected [8]. Intensity-modulated RT (IMRT) is now the standard technique. IMRT delivers a more precise and conformed radiation dose, allowing irradiation of the selected target volume. In the era of precision medicine, the routine use of traditional RT for the treatment of NPC is currently being challenged due to advancements in diagnostic and therapeutic techniques. As target volume delineation has become more sophisticated, evidence-based consensus guidelines for target volumes in NPC have been suggested [9]. In addition, the accumulated tumor control and failure pattern data, after selected target volume irradiation, have led to significant advances in Less is more: level IB-sparing radiation therapy in nasopharyngeal cancer