Brachytherapy (Interventional Radiotherapy) for Squamous Cell Carcinomas of the Nasal Vestibule: Optimization of Dose and Technique A Multicenter Prospective Registration Study Endorsed by HNS GEC-ESTRO WG

Rationale: Primary brachytherapy (also known as Interventional Radiotherapy, IRT) achieves high cure rates in cancer of the nasal vestibule (CNV) while preserving nasal aesthetics and function. In our recently published nationwide multicenter study, brachytherapy (BT) increased nose preservation probability from 61 to 82 % compared to external beam radiotherapy (EBRT). Although late toxicity was more common following BT, it was predominantly CTCAE grade 1-2 and deemed acceptable given the substantial benefit in local control and nose preservation.

However, a notable finding of our study was the substantial variation in BT practice, including implantation techniques, dose prescriptions, and treatment planning. Although this analysis covers one of the largest series of CNV patients to date, patient numbers were insufficient to reliably compare the efficacy of the different application/implantation techniques and doses. The retrospective design of the study proved inappropriate for a detailed analysis of the dose-volume data, which is necessary to correlate implantation and dose data to outcome. As the integral brachytherapy dose, as well as the dose inhomogeneity in tissue may vary widely depending on how the dose is prescribed, simple prescription doses are insufficient to characterize a brachytherapy plan comprehensively.

Given the excellent disease control achieved with BT, optimizing aesthetic and functional outcomes while minimizing toxicity becomes increasingly important. Therefore, to optimize BT treatment for CNV and facilitate its wider adoption, detailed prospective data collection on treatment parameters, dose plans, toxicity (both physician-reported and patient-reported), oncological outcomes, and functional results is necessary. This study is designed as a non-comparative, descriptive prospective registry aimed at systematically documenting current international practice in brachytherapy for cancer of the nasal vestibule.

Objective: To prospectively describe BT treatment techniques, parameters, oncological outcomes, acute and late toxicity and patient satisfaction; and to correlate these outcomes with treatment parameters. Specifically, to establish dose-response relationships for oncological control, toxicity, and functional outcomes.

Study design: Prospective observational multicentre registration study. Study population: Adults with a squamous cell squamous cell carcinoma of the nasal vestibule, considered suitable for primary brachytherapy.

Main study parameters/endpoints: To describe treatment techniques, dose prescriptions and brachytherapy dose plans in terms of dose-volume parameters. Oncological outcomes include details on recurrence and cancer-specific survival. Toxicity, patient satisfaction, and QoL will be assessed with validated patient questionnaires as through applicable CTCAE (physician based).