Measures

SEER collects data on patient demographics, tumor site, stage, and treatment. For patients with well differentiated thyroid cancer, the analysis included information on age, SEER defined race or ethnicity (included to correct for racial disparities), median household income by geographical region, percentage of population over age 25 years of the geographical region with only a high school diploma, tumor size (<1.0 cm, 1.0-1.9 cm, 2.0-3.9 cm, and >4 cm), tumor histology, and SEER stage at diagnosis. The type of initial surgery (characterized as no surgery, lobectomy, or total thyroidectomy) and presence or absence of initial lymph node resection were included.

SEER-Medicare data were used to obtain information on imaging after primary treatment. We used Current Procedure Terminology (CPT) codes to identify the type of imaging used. Neck ultrasounds were identified by CPT code 76536. Radioiodine scans were identified by CPT codes 78015, 78016, 78017, 78018, 78020, 78800, 78801, 78802, and 78804. We excluded the first billing of radioiodine scans done, because we thought that they were likely to be part of initial staging and not used for surveillance. Positron emission tomography (PET) scans were identified by CPT codes 78810, 78811, 78812, 78813, 78814, 78815, and 78816.

We also used SEER-Medicare CPT codes to identify treatments for recurrence. Codes used to identify repeat neck surgeries were 38510, 38520, 38720, 38724, and 60260. Codes used to identify radioactive iodine treatment were 79005, 79030, and 75035. We omitted the first billing for radioactive iodine treatment that was performed to avoid including ablation that was done as part of primary treatment for differentiated thyroid cancer. The CPT codes used to identify radiotherapy were 77261, 77262, and 77263.

The mortality data reported by SEER were provided by the National Cancer for Health Statistics.^{20 22} SEER uses algorithms to process causes of death from the death certificate in order to identify a single, disease specific, underlying cause of death.²⁰ SEER disease specific survival is defined as the time interval from diagnosis to death from differentiated thyroid cancer or time of censoring.