O005

Thursday, November 13th, 2025 17:30 – 17:40
Speaker Xuanhe Hou

Comparison of Conventional Radiotherapy and VMAT with Different PTV Margins for Early Glottic Cancer: Dosimetric and Clinical Outcomes

Purpose/Objectives
Local radiotherapy (RT) for early glottic cancer was traditionally delivered with standard lateral beams encompassing the entire larynx. With the introduction of conformal techniques such as volumetric modulated arc therapy (VMAT), more targeted approaches have become routine. However, evidence directly comparing treatment-related toxicity between conventional RT and VMAT remains limited, and few studies have assessed whether reducing planning target volume (PTV) margins in VMAT can mitigate toxicity while preserving local control. In this retrospective cohort study, we compared conventional RT, VMAT with wider PTV margins, and VMAT with narrower PTV margins to evaluate post-treatment outcomes.
Materials/Methods
Between 2010 and October 2024, 259 patients with early glottic cancer received local RT to a dose of 60-68 Gy in 2.0-2.4 Gy per fraction. We split the cohort in three groups depending on the RT techniques used during this period. Group 1 (n = 39) underwent conventional RT with two opposed lateral wedge-pair fields to the entire larynx. Group 2 (n = 106) received VMAT to a PTV with wide margins (10 mm in axial plane; 12 mm in craniocaudal direction) around the glottic (single cord) gross tumor volume (GTV)-based clinical target volume (CTV), using kV-kV verification with bony match on the vertebral column. Group 3 (n = 114) received VMAT to a PTV with smaller margins (respectively 3 mm axial and 5 mm craniocaudal) around the same CTV as in group 2, incorporating a “Do Not Swallow” instruction during VMAT and daily online cone-beam computed tomography (CBCT) verification with thyroid cartilage matching.
Side-effects and oncological outcomes were prospectively registered within the routine follow-up program (ClinicalTrials.gov Identifier: NCT01985984). Acute and late physician-rated toxicities were assessed using Common Terminology Criteria for Adverse Events (CTCAE) version 4, covering dysphagia, aspiration, xerostomia, weight loss, laryngeal oedema, mucositis, radiation dermatitis, neck fibrosis, osteonecrosis, and hypothyroidism.
Results
The median follow-up for patients alive at last follow-up was 120 months for group 1, 105 months for group 2, and 47 months for group 3. Doses to all relevant organs at risk (Dmeans) were significantly lower for group 3 compared with group 2, including the carotid arteries, spinal cord and the swallowing muscles, see table 1. Group 3 experienced significantly lower rates of most acute and late toxicities, including dysphagia, aspiration and mucositis, while no differences were observed in e.g. hypothyroidism or osteonecrosis (Table 2). There were no significant differences in local control (p = 0.468) and overall survival (p = 0.141) between the three groups. The 2- and 3-year local control rates were 94.4% and 90.9% for Group 1, 94.9% and 92.6% for Group 2, and 96.3% and 96.3% for Group 3. The corresponding 2- and 3-year overall survival rates were 94.7% and 92.1%, 93.3% and 87.5%, and 92.9% and 86.3%, respectively.
Conclusions
Compared to historical controls receiving RT with wider margins, early-stage glottic cancer
patients receiving localized radiotherapy using VMAT with smaller PTV margins and daily CBCT-based matching resulted in lower toxicity rates, while maintaining high local control rates.

Keywords: radiotherapy, glottic cancer, intensity-modulated, toxicity