Seeing More to Treat Better: Ultra-High Frequency Ultrasound as a Decision-Shaping Tool in Radiotherapy for Head and Neck Non-Melanoma Skin Cancer in a Single-Institution Feasibility Study

Background/Objectives: Accurate target delineation is critical in radiotherapy for head and neck non-melanoma skin cancer (NMSC), where tumor depth and subclinical extension are often underestimated by clinical and dermoscopic assessment alone. While high frequency ultrasound has shown value in surface-based radiotherapy techniques, the role of ultra-high frequency ultrasound (UHFUS) within external beam radiotherapy (EBRT) workflows remains poorly defined. Methods: We conducted a single-institution observational feasibility study including all consecutive patients with head and neck NMSC treated with definitive or adjuvant radiotherapy between July 2022 and July 2023 using a structured multidisciplinary workflow integrating pre-treatment UHFUS. UHFUS was systematically performed prior to CT simulation and incorporated into radiotherapy planning. The primary endpoint was the impact of UHFUS on radiotherapy decision-making, predefined as modification of target delineation, treatment intent, or beam modality selection. Secondary endpoints included feasibility, early local control, and late toxicity (descriptive). Results: Thirty patients were included (median age 85 years; range 66–99). UHFUS influenced at least one decision endpoint in 13 patients (43.3%). In the definitive radiotherapy cohort (n = 18), UHFUS modified gross tumor volume delineation in eight patients (44.4%), with an increase in median GTV from 17.5 cm3 to 24.3 cm3. Among patients initially referred for adjuvant radiotherapy (n = 12), UHFUS identified macroscopic residual disease in two cases, leading to a change in treatment intent from adjuvant to definitive radiotherapy. UHFUS supported beam modality selection in three patients by enabling safe use of electron therapy for superficial lesions. After a median follow-up of 24 months (range 12–24), no local recurrences were observed. Late toxicity was limited to grade 1 cutaneous events. Conclusions: Integration of UHFUS into EBRT planning for head and neck NMSC is feasible and clinically informative. UHFUS acts as a decision-shaping tool, influencing target delineation, treatment intent, and modality selection within a multidisciplinary workflow. These findings support further prospective evaluation of UHFUS-guided radiotherapy planning to standardize decision algorithms and assess long-term clinical impact.