To determine the superiority of intensity-modulated radiation therapy (IMRT) over three-dimensional conformal radiation therapy (3DCRT) in patients who underwent intra-arterial chemoradiotherapy for oral cancer.

We retrospectively analyzed patients with locally advanced oral cancer curatively treated with intra-arterial chemoradiotherapy at a single institution between 2010 and 2021. All patients treated after May 2015 underwent IMRT. Docetaxel (12 mg/m²/week) and nedaplatin (5 mg/m²/day) were administered through a shallow temporal artery using a catheter.

In total, 143 patients (IMRT: 71; 3DCRT: 72) were included in this study. The 5-year overall survival (OS) and progression-free survival (PFS) rates were 75.7 % and 59.8 %, respectively, with no significant differences between the irradiation methods. In multivariate analysis, cervical lymph node metastasis (LNM) was the only significant poor prognostic factor contributing to OS, PFS, locoregional control (LRC), and local control (LC). In multivariate subgroup analysis of LNM cases (n = 90), IMRT contributed to favorable LRC (hazard ratio [HR]=0.4, P = 0.01) and LC (HR=0.4, P = 0.006). There was no difference in the incidence of grade ≥2 osteonecrosis of the jaw (4.2 % vs. 12.5 %, P = 0.13), xerostomia (75 % vs. 82 %, P = 0.316), or dysgeusia (80 % vs. 82 %, P = 0.834) between the IMRT and 3DCRT groups. However, the rates of xerostomia at 6 months and dysgeusia at 3 months were lower in the IMRT group (both P < 0.001).

IMRT neither improved patient survival nor significantly reduced the incidence of osteonecrosis of the jaw. However, it demonstrated favorable LRC and LC in patients with LNM, suggesting an advantage in early recovery from xerostomia and dysgeusia.