Purpose

Recurrent head and neck cancers, involving paranasal sinus and skull base in previously irradiated patients, present significant challenges due to proximity of critical organs. We evaluated the feasibility and safety of a hybrid approach combining 3D-printed interstitial brachytherapy (ISBT) and stereotactic body radiotherapy (SBRT) for re-irradiation.

Material and methods

A 39-year-old male with a history of adenoid cystic carcinoma (ACC) of the right petrous apex and Meckel’s cave, initially treated with sub-total resection and 66 Gy radiotherapy in 2017, presented six years later with recurrence in the right nasal cavity extending to the medial orbital wall. Following endoscopic debulking, a residual lesion (1.8 cm × 1.6 cm × 1.2 cm) remained. A hybrid re-irradiation strategy was employed, consisting of template-guided ISBT (8 Gy in 2 fractions) using a customized 3D-printed orbital applicator, followed by volumetric modulated arc therapy (VMAT)-based SBRT (40 Gy in 10 fractions).

Results

The hybrid course delivered a cumulative physical dose of 41.82 Gy (ISBT D₉₀ of 2.64 Gy, and SBRT D₉₅ of 39.18 Gy). The total lifetime cumulative EQD₂ to the right optic nerve reached 82.04 Gy (α/β = 3 Gy), including 31.54 Gy from the current course. Lifetime cumulative EQD₂ values for the right globe and lens were 33.85 Gy and 11.6 Gy, respectively. Treatment was well-tolerated, with no grade 3 toxicity observed. MRI at six months demonstrated a complete radiologic response, and the patient remained asymptomatic with preserved vision at 12 months post-treatment.

Conclusions

This case demonstrates the feasibility and safety of hybrid ISBT-SBRT approach for recurrent orbital ACC. In anatomically complex sites, this strategy allows optimal target coverage while respecting organ at risk (OAR) constraints.