157 - Postoperative Hypofractionated Radiotherapy for Thymic Epithelial Tumors: Efficacy and Safety Results from a Prospective, Single-Center, Phase II Trial

08:30am - 08:40am ET

Room 157

Presenter(s)

Zhihui Zhang, MD, PhD - National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy, Beijing, Beijing

T. Zhang, Z. Zhang, D. Gao, X. Guo, and N. Bi; Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Purpose/Objective(s): Postoperative radiotherapy (PORT) is the standard adjuvant treatment for Masaoka–Koga stage II–III thymic carcinoma and stage IIB–III thymoma following R0 resection. While hypofractionated radiotherapy has emerged as a standard in multiple malignancies to improve treatment efficiency, prospective data in thymic epithelial tumors (TETs) are lacking. This phase II study evaluated the efficacy and safety of moderately hypofractionated PORT (45 Gy in 15 fractions) in this patient population.

Materials/Methods: This prospective, single-arm, phase II trial enrolled patients aged 18–75 years with pathologically confirmed TETs and an ECOG PS of 0–1. All the patients received R0 resection. Specifically, Masaoka–Koga stage II–III thymic carcinoma and Masaoka–Koga stage IIB (Type B2/B3) to III thymoma were included. All patients received adjuvant intensity modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) to a total dose of 45 Gy in 15 fractions (3 Gy/fraction, BED10 = 58.5 Gy). The primary endpoint was disease-free survival (DFS). Secondary endpoints included overall survival (OS), patterns of failure (local, intrathoracic, and distant), and treatment-related toxicities (CTCAE v5.0). Survival outcomes were estimated using the Kaplan–Meier method.

Results: Of the 50 patients enrolled (median age, 55 years; range, 27–75), 31(62.0%) were male. Pathological subtypes included thymic carcinoma (56.0%) and thymoma (44.0%). At a median follow-up of 14.2 months (range, 1.5–21 months), the 1-year OS and DFS rates were 100% and 98.0%, respectively. Neither median OS nor DFS was reached. Notably, no local or intrathoracic failures occurred; two patients (4%) developed distant metastases. All patients completed the prescribed radiotherapy without treatment delays. The regimen was well-tolerated with no grade =3 toxicities. Only one patient (2%) experienced grade 2 radiation pneumonitis. No symptomatic (grade =2) esophagitis, cardiac toxicity, or late vascular events were observed.

Conclusion: Moderately hypofractionated PORT (45 Gy/15 fractions) provides promising early local control and a favorable safety profile for patients with resected TETs. By significantly reducing the treatment duration (3 weeks vs. 5 weeks), this accelerated regimen offers a high-value alternative to conventional fractionation. Further long-term surveillance and prospective multi-institutional validation with large sample size are warranted.

Trial registration: ClinicalTrials.gov: NCT06189183. Registered on December 18, 2023.

Abstract 157 - Table 1: Baseline Clinicopathological Characteristics

Characteristic	Statistics (N=50)
Age (years), median (range)	55(27-75)
Gender, n(%)
Male	31(62.0%)
Female	19(38.0%)
Masaoka Stage, n(%)
II	33(66%)
III	17(34%)
Pathology
Thymic Carcinoma	28(56.0%)
Thymoma	22(44.0%)
Smoking Status,n(%)
Never smoker	31(62.0%)
Current/Former smoker	19(38.0%)