Concurrent chemoradiotherapy with combined irradiation techniques of volumetric-modulated arc therapy (VMAT) and simultaneously integrated inner-escalated boost (SIEB) successfully managing a patient with cT4 nasopharyngeal carcinoma with limited toxicities: a CARE-compliant case report

Background: Nasopharyngeal cancer (NPC) is prevalent in South Asia, including Taiwan. For patients with locoregionally advanced NPC, definitive concurrent chemoradiotherapy (CCRT) followed by adjuvant chemotherapy or after induction chemotherapy is standard treatment. However, local recurrence remains a primary cause of treatment failure, especially in locally advanced cT4 NPC with intracranial extension. We reported a case of cT4 NPC successfully managed with precise radiotherapy (RT) techniques that enabled simultaneous intratumor dose escalation and extratumor dose attenuation, resulting in durable disease-free survival (DFS) with limited treatment-related toxicities, and good post-irradiation bony regeneration.

Case Description: A 64-year-old man without significant comorbidities presented with refractory headache, epistaxis for about three months, and double vision for one month. The patient was diagnosed undifferentiated non-keratinized carcinoma of the nasopharynx, cT4 (intracranial invasion) N2M0, clinical stage IVA [American Joint Committee on Cancer (AJCC) 7^th edition], treated with definitive CCRT followed by adjuvant chemotherapy. RT was delivered using volumetric-modulated arc therapy (VMAT) with a simultaneously integrated inner-escalated boost (SIEB). A total dose of 72 Gy in 40 fractions was prescribed to gross tumor volumes, with a simultaneous intra-tumoral boost of 80 Gy and extratumor attenuation of 60 Gy. Acute toxicities included Grade 4 neutropenia with febrile neutropenia and Grade 3 mucositis after the first cycle concurrent chemotherapy, which resolved after medical management. Subsequent treatment was well tolerated with only Grade 2 dermatitis and mucositis, and no severe late toxicities. Post-treatment imaging studies demonstrated persistent reparative soft tissue replacement of the clivus without abnormal enhancement, regression of non-contrast-enhanced soft tissue and progressive skull base bone regeneration. At 136 months of follow-up, no evidence of cancer recurrence was observed, with significant post-irradiation bony regeneration.

Conclusions: In this case of locally advanced cT4 NPC, using CCRT incorporating VMAT with SIEB techniques, followed by adjuvant chemotherapy, achieved durable DFS with acceptable toxicity. These findings suggest that VMAT SIEB is a viable and accessible strategy for managing cT4 NPC, using precise intra-tumoral dose escalation associated with sustained tumor control, and remarkable skull base bone remodeling. Therefore, prospective studies are warranted to define the clinical benefit and reproducibility of this approach.