Definitions
Tracheal invasion stage I (Shin I) was defined as disease invading
through the capsule of the thyroid gland and abutting but not invading
the external perichondrium of the trachea.[14] Tracheal invasion
stage II (Shin II) was defined as invasion of the disease between the
rings of the cartilage or as invasion such as to cause minor cartilage
destruction.[14] Minimal ETE was defined as peri-thyroidal fat
involvement diagnosed on final pathology without strap muscle or neck
structure invasion according to the latest revision
(8th edition) of the AJCC staging manual.[15]
Gross ETE was defined according to the updated AJCC as including any
strap muscle, subcutaneous soft tissue, larynx, trachea, esophagus, and
RLN involvement.[15] Margins were considered R0 if frozen section
analysis and/or final pathology confirmed that the soft tissue or
cartilaginous margins were tumor-free.[16] Margins were considered
microscopically invaded (R1) if histological analysis showed tumor at
the margin of the operating specimen or <1 mm from the
margin.[16] Dosimetry parameters of the delivered RAI were retrieved
from treatment plans.
Local control was defined according to the 2015 American Thyroid
Association Management Guidelines for Adult Patients with Thyroid
Nodules and Differentiated Thyroid Cancer:[17] An “excellent”
response was defined as no clinical, biochemical, or structural evidence
of disease. A “biochemical incomplete” response was defined as
abnormal thyroglobulin or rising anti-thyroglobulin antibody levels in
the absence of localizable disease. A “structural incomplete” response
was defined as persistent or newly identified loco-regional or distant
metastases. Event-free survival was defined as survival without
macroscopic local, regional, or distant disease visible on imaging, with
or without persistent stable biochemical disease. Disease-free survival
(DFS) was defined as survival without any evidence of disease at any
site. OS was defined as death due to any cause. The treatment
termination date was used as time point zero.