Target-prioritized IMRT for nasopharyngeal carcinoma with tumor proximity to the spinal cord: clinical feasibility and long-term outcomes.

Objectives: For locally advanced nasopharyngeal carcinoma (NPC) with tumor close to the cervical spinal cord, strict spinal cord constraints may compromise target coverage. We evaluated the feasibility and safety of a target-prioritized IMRT strategy in this setting. Materials and methods: We retrospectively reviewed 909 consecutive patients with stage III-IVB NPC treated with IMRT between 2012 and 2022. Among 145 patients with tumour-cord proximity, 106 (73.1%) received a target-prioritized strategy, when adequate target coverage could not be achieved under conventional constraints. Dosimetric parameters were extracted from dose-volume histograms. Predictors were evaluated by logistic regression and a cumulative cranio-cervical burden score. Outcomes were analyzed using Kaplan-Meier and log-rank test. Results: With a median follow-up of 76.11 months, no clinically diagnosed radiation myelopathy (RM) was observed in the overall cohort (upper one-sided 95% CI, 0.33%). The 5-year local relapse-free survival (LRFS) and overall survival (OS) were 92.8% and 86.8%. The cumulative burden score, based on occipital base, occipital condyle, and atlanto-dental interval involvement, was associated with target-prioritized planning (trend OR, 1.906; P = 0.001). In the target-prioritized cohort, median cord Dmax was 56.2 Gy, and 22 patients (20.8%) had a Dmax >60 Gy, while high-dose volumes remained limited. With a median follow-up of 93.24 months in this cohort, 5-year LRFS and OS rates were 87.9% and 74.2%, respectively, and no clinically diagnosed RM was observed (upper one-sided 95% CI, 2.8%). Conclusion: With strict dose-volume control and image guidance, target-prioritized strategy appears feasible in selected NPC cases but does not support modification of current spinal cord constraints.