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Published on: April 16, 2019
Failure patterns relative to radiation treatment fields for stage II-IV thymoma
Andreas Rimner1, Daniel R Gomez, Abraham J Wu
1Departments of *Radiation Oncology, †Thoracic Surgery, ‡Thoracic Oncology, §Pathology, ¶Epidemiology and Biostatistics, and ‖Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York; Departments of #Radiation Oncology and **Thoracic Surgery, The University of Texas MD Anderson Cancer Center, Houston, Texas; and ††Department of Radiation Oncology, Mt. Sinai Medical Center, New York, New York.
Introduction:
The optimal radiation therapy (RT) field design for thymomas remains unclear. Here we report the failure patterns in stage II-IV thymoma after RT at two tertiary referral centers, classified according to the new International Thymic Malignancy Interest Group definitions.
Methods:
We reviewed 156 stage II-IV patients with thymoma treated with definitive (n=24) or adjuvant (n=132) RT. All RT was delivered without elective nodal irradiation (median dose 5040 cGy). Intrathoracic failures were classified as (1) in-field failures (within 100% isodose line [IDL]), (2) marginal recurrences (<100% and ≥50% IDL), and (3) out-of-field failures (outside the 50% IDL).
Results:
The median follow-up was 61 months. Surgical margins were positive in 39%. The median tumor size was 9 cm. The 5-year cumulative incidence of all intrathoracic failures was 24% (n=34). Failures occurred within the RT field (n=5), marginally (n=1), out-of-field (n=22), and synchronously in- and out-of-field (n=6). The 5-year cumulative incidence of in-field failures was 7%. These were associated with Masaoka stage and tumor size. Macroscopically positive margins were associated with more local failures. Intrathoracic failures occurred most commonly in the pleural space (n=29) and lymph nodes (n=9). Patients with more advanced stage, and those treated with intensity-modulated radiation therapy had more intrathoracic failures. RT dose and chemotherapy did not impact failure patterns.
Conclusions:
Although there were few in-field failures in patients who received RT for stage II-IV thymomas, a high rate of out-of-field intrathoracic failures still occurred. Further study is necessary to identify treatment approaches that prevent pleural recurrences.
