Failure patterns relative to radiation treatment fields for stage II-IV thymoma

J Thorac Oncol. 2014 Mar;9(3):403-9. doi: 10.1097/JTO.0000000000000099.


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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Female
  • Follow-Up Studies
  • Humans
  • Lung Neoplasms / mortality
  • Lung Neoplasms / pathology
  • Lung Neoplasms / radiotherapy*
  • Male
  • Middle Aged
  • Neoplasm Staging
  • Retrospective Studies
  • Thymoma / mortality
  • Thymoma / pathology
  • Thymoma / radiotherapy*
  • Thymus Neoplasms / mortality
  • Thymus Neoplasms / pathology
  • Thymus Neoplasms / radiotherapy*
  • Treatment Failure
  • Young Adult