KEY POINTS
- This single-center retrospective study included 99 patients with nasopharyngeal carcinoma treated with definitive VMAT between 2023 and 2024. 48 patients used an individualized 3D-printed intraoral stent and 51 received no intraoral device.
- The personalized stents were fabricated from polylactic acid using 3D printing and maintained approximately a 2-cm mouth opening while reproducibly positioning the mandible and tongue. Daily cone-beam CT was then used to assess interfraction anatomical variation.
- At one year, hearing impairment was reported in 33.3% with the stent versus 88.2% without it (p<0.0001), dysphagia in 37.5% versus 74.5% (p=0.001) and dysgeusia in 35.4% versus 82.4% (p<0.0001). Xerostomia occurred in everyone but was substantially less severe in the stent group.
- Severity differences were particularly striking. No stent-treated patient had grade 3–4 hearing impairment, compared with 45.3% of controls; grade 3–4 dysphagia occurred in 2.1% versus 37.3%, respectively.
- Daily imaging suggested a geometric mechanism. The stent reduced positional variability in several directions for the tongue, mandible and left parotid—for example, posterior-tongue left-right variability was 0.098 ± 0.087 versus 0.132 ± 0.150 mm (p=0.01) and middle-tongue variability 0.118 ± 0.138 versus 0.149 ± 0.140 mm (p=0.019).
- Dosimetry also favored the stent group. Median tongue mean dose was approximately 46 versus 53 Gy (p=0.032), and irradiated tongue volume was 72.4 versus 92.9 (p=0.016). Several temporomandibular-joint and inner-ear dose measures were also reduced.
- Interpretation requires substantial caution: stent use was chosen by the physician and patient rather than randomized, with factors including oral anatomy, affordability and preference influencing selection. Toxicity was assessed at a single follow-up time point, cumulative delivered dose was not reconstructed, and formal dose–response analysis of tongue subregions was not performed.
CLINICAL TAKEAWAY
The study suggests that an intraoral stent may do more than simply push normal tissue away from the target: reproducible positioning throughout treatment may itself reduce unintended dose. The magnitude of the toxicity differences makes prospective validation worthwhile, but these observational data are not strong enough to conclude that the device itself caused the improvement.