Radiotherapy for Thymic Malignancies: Teaching Lecture from ESTRO Congress
During his teaching lecture at ESTRO Congress, Dr. Andreas Rimner (University Hospital Freiburg, Germany) reviewed the current role of radiotherapy in thymic malignancies, addressing the key clinical questions of what to treat, when to treat, and how to deliver treatment in a disease group characterized by rarity, heterogeneity, and evolving evidence. He highlighted that recent progress in the field has been driven by large retrospective database analyses, smaller prospective studies, and emerging randomized data, which together have improved understanding of indications, target definition, and expected oncologic outcomes.
From a “what to treat” perspective, he emphasized that radiotherapy target volumes are strongly dependent on clinical context. In the neoadjuvant or definitive setting for unresectable disease, the gross tumor volume with appropriate margins represents the primary target, with inclusion of involved
lymph nodes where applicable. In the postoperative setting, postoperative radiotherapy (PORT) focuses on the tumor bed and areas at risk, but accurate delineation requires integration of pre- and post-treatment imaging, surgical reports, pathology findings, and intraoperative information. multidisciplinary collaboration and communication with surgeons are essential for radiotherapy treatment decision-making and planning.
Dr. Rimner also highlighted the complexity of defining R1 disease and surgical margins in the mediastinum, where anatomical boundaries are variable and often inconsistently reported. In this context, he referenced structured surgical documentation approaches such as ITMIG templates to improve consistency in target definition. It should be noted that elective nodal irradiation has no established role due to a lack of benefit and increased adverse events, including higher rates of esophagitis, particularly in larger tumors.
Regarding treatment indications, Dr. Rimner explained that radiotherapy use is closely linked to disease stage and resectability. Postoperative radiotherapy appears to provide benefit in completely resected stage II–III thymomas and in locally advanced thymic carcinomas, while its role in early-stage disease remains uncertain and must be balanced against potential long-term adverse events. In incompletely resected disease, PORT is generally supported by oncologic principles and available clinical data. He also emphasized that thymic carcinoma behaves more aggressively than thymoma, with a higher propensity for distant metastases, and that current evidence supports a clearer role for postoperative radiotherapy in R0–R1 resected advanced thymic carcinoma, while data in early stages remain insufficient. Across available studies, most evidence is still based on the Masaoka–Koga staging system. He further noted that pleural and pericardial relapse represent the most common sites of recurrence, and that patients with pleural metastases may experience prolonged survival, with long-term disease trajectories extending over many years in selected cases.
Regarding “how to treat,” Dr. Rimner highlighted the importance of modern conformal radiotherapy techniques, including IMRT, VMAT, and proton therapy, which allow improved target coverage while reducing dose to surrounding critical structures such as the heart, lungs, esophagus, and spinal cord.
Postoperative radiotherapy is generally delivered using conventional fractionation, with typical dose ranges of:
- 45–50.4 Gy after R0
- 54–60 Gy after R1
- 60–66 Gy after R2
Definitive treatment doses are typically 60–66 Gy, often combined with chemotherapy depending on the clinical scenario.
Dr. Rimner also discussed the role of SBRT in selected cases of pleural metastases or oligoprogression, as well as the potential advantages of proton therapy in thymic tumors due to the anterior mediastinal location and the long-term risk profile of these generally indolent malignancies in relatively younger patients.
In conclusion, the teaching lecture emphasized that radiotherapy in thymic malignancies requires a structured approach across all stages of care: defining appropriate targets (tumor, tumor bed, involved nodes, or pleural/pericardial disease), selecting the correct timing (preoperative, postoperative, definitive, recurrent, or palliative), and applying modern highly conformal techniques, most commonly with conventional fractionation, while selectively incorporating SBRT and particle therapy in carefully chosen patients.