ESTRO 2024 - Abstract Book

S1778

Clinical - Lung

ESTRO 2024

Between November 2018 and May 2023, our center treated 11 patients with a total of 25 thymoma metastases (Table 1). All patients had previously undergone surgical resection of the primary tumor, with or without neoadjuvant chemotherapy, followed by adjuvant radiation therapy (RT), except in one case. The approach for managing the thymoma recurrences was discussed in multidisciplinary setting. Most lesions were located in the pleura (12 cases), and the remainder in the lungs (4 cases) and extrathoracic sites (3 cases). SBRT was delivered in 5 fractions for all cases, using Varian TrueBeam with FFF-RapidArc and daily kV-CBCT with a mean dose of 33.75 Gy (range 30 Gy-40 Gy), and a mean BED10Gy of 58.5 Gy (range 48 Gy-72 Gy). The mean planning target volume (PTV) volume was 48.4 cm³ (range 5.5 cm³ – 121.7 cm³).

Results:

The median follow-up (FUP) duration was 15 months (range: 3-24 months). During the follow-up, one patient succumbed to a different cancer histology (breast cancer). No relapse within the RT field was observed, and the treatments were well-tolerated, with only one case of acute esophageal toxicity grade 1 (G1). Four patients experienced a second metastasis, two experienced a third one, and one patient faced a fourth progression. All new lesions were treated with SBRT. At 3-month FUP, 50% of patients achieved a partial response (PR), 40% attained a complete response (CR), and 10% experienced systemic disease progression. At the 6-month FUP, PR was observed in 57.1% of patients, and CR was achieved in 42.9%. Among the five patients who reached the 2-year FUP milestone, RP was maintained in 100% of cases.

The data presented in this report highlight the potential of SBRT as a valuable approach for recurrent thymoma. Several key findings emerge from our research:

1. Overall Safety: SBRT proved to be a well-tolerated treatment modality, with minimal acute and late toxicities. The solitary case of acute esophageal toxicity G1 highlights the safety profile of SBRT, indicating that it can be administered with confidence to a select group of patients.

2. Excellent Local Disease Control: Our study demonstrated no relapse within the RT field, indicating that SBRT is effective in achieving local disease control in the context of thymoma recurrence.

3. Multifocal Lesion Management: SBRT's ability to treat multiple lesions simultaneously is a significant advantage in the management of oligorecurrent thymoma, as our data revealed that patients often face multiple relapses. This multifocal approach streamlines the treatment process and enhances patient outcomes.

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