Long-term Outcomes of Carbon-ion Radiotherapy for Inoperable Locally Advanced Olfactory Neuroblastoma

Radiotherapy (RT) is recommended for inoperable locally advanced olfactory neuroblastoma (ONB); however, previous studies have reported poor outcomes with photon RT, highlighting the need for more effective local treatment modalities. This study aimed to evaluate the safety and efficacy of carbon ion radiotherapy (C-ion RT) for ONB.

We retrospectively analyzed the medical records of 22 patients with inoperable ONB who underwent C-ion RT between September 2002 and July 2022. C-ion RT was administered at a relative biological effectiveness-weighted dose of 60.8 Gy in 16 fractions over four weeks.

The median follow-up duration was 63.2 months (range=7.1-199.3 months). The 5-year local control, overall survival, and progression-free survival rates were 70.8%, 78.3%, and 42.0%, respectively. Of the six patients (27.3%) who experienced local recurrence, five had in-field recurrences, and one had a marginal recurrence. Eight patients (36.4%) developed cervical lymph-node metastases, and six patients (27.3%) developed distant metastases. Late adverse events of ≥ Grade 3 occurred in six patients (27.3%). Among these, one patient (4.5%) developed Grade 3 radiation-induced brain injury. Optic nerve disorders of ≥ Grade 3 occurred in five patients (22.7%), including three with Grade 4 visual loss on the affected side; however, this severe complication was anticipated prior to treatment due to tumor proximity and the high radiation dose required for tumor control.

C-ion RT is a promising treatment option for inoperable locally advanced ONB, offering acceptable toxicity and favorable therapeutic efficacy.