Abstract
Purpose : The date of surgery or radiotherapy (RT) was not recorded in the National Health Insurance database until Jan. 1, 2011, which limits the calculation of the exact time interval between treatments. Our purpose is to formulate and validate a surrogate estimate for the time interval between surgery and adjuvant RT. Materials and Methods: Information of patients with malignant brain tumors diagnosed and treated with surgery and adjuvant RT between Jan. 1, 2011 and Dec. 31, 2012 was obtained from the National Health Insurance (NHI) database and retrospectively analyzed. The surrogate estimate for the interval between surgery and RT was formulated according to the date of outpatient visits and the first date of hospitalization. Surrogate estimate of the interval was validated with the exact interval calculated by the later coded dates of surgery and RT from the database, using the best-fitting linear regression. Results: 1,527 cases of malignant brain tumors were defined according to ICD-9 diagnosis code. 394 cases were excluded for the presence of other cancer diagnoses. Among the remaining 1,133 cases, 463 cases receiving both brain tumor excision and adjuvant RT were analyzed. Surrogate estimate of time intervals and exact time intervals correlate well with a slope of 1.0076, a y-intercept close to -1 day, and an R2 of 0.8633. The calculation is further improved to an R2 of 0.9809 with a slope of 0.9951 and a y-intercept close to 5 days, by excluding cases with surrogate estimates of an interval smaller or equal to 0. Conclusion: Our validated surrogate estimate of the interval between surgery and adjuvant RT provides a possible method to overcome the limitation of inadequate date information before Jan. 1, 2011, and therefore enables the application of most of the data from the Health and Welfare Database for research regarding the effect of RT delay on cancer outcomes.
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