Smaller Radiation Fields Linked to Lower Toxicity in Advanced Differentiated Thyroid Cancer

External beam radiotherapy is used for selected patients with high-risk, residual, unresected, or recurrent differentiated thyroid cancer when further surgery is not recommended. This single-center retrospective study examined 284 patients with available radiation plans among 327 consecutive patients treated from 1999 to 2023. Fields were comprehensive in 103 patients, ipsilateral in 116, and central-compartment only in 65. Investigators assessed acute and late toxicity and locoregional recurrence, accounting for death as a competing risk; median follow-up was 8.9 years.

Acute grade ≥2 xerostomia occurred in 36%, 17%, and 16% of the comprehensive, ipsilateral, and central groups, respectively (p=0.002). Corresponding dysphagia rates were 58%, 48%, and 36% (p=0.02). Voice changes and fatigue also differed significantly across groups. Late grade ≥2 dysphagia occurred in 23%, 6%, and 8%, respectively (p=0.0004). Gastrostomy tube placement was more frequent with comprehensive fields than with either reduced-field approach.

In-field failure rates were 10.7%, 9.5%, and 7.7%, respectively, with no significant difference in locoregional control (p=0.88). Six patients receiving central-only radiation developed out-of-field lateral neck recurrences; all were successfully salvaged surgically.

The findings support further evaluation of individualized field reduction, but do not establish equivalent tumor control. Retrospective selection, the single-center setting, and the long treatment period limit interpretation. Prospective multicenter studies are needed before drawing firm conclusions about de-escalation; only the abstract was available for this report.