Toward Redefining Adherence: The Impact of Adherence Definition on Lung Cancer Screening Program Benchmarks.

[BACKGROUND] Annual low-dose CT (LDCT) is recommended after a negative lung cancer screening (LCS) CT. Patient follow-up is inconsistent, varying in both timing and imaging type (LDCT or routine chest CT). This study evaluates how different definitions of adherence to follow-up affect LCS adherence rates.

[STUDY DESIGN AND METHODS] This retrospective study (2016-2023) evaluated LCS follow-up within a New York health care system. Binary adherence was defined as follow-up chest CT acquisition and evaluated using six definitions of adherence. Variables included (1) three follow-up time frames (15, 24, and unlimited months) and (2) two follow-up CT types (LDCT only versus any chest CT). A generalized linear model assessed the impact of time frame and CT type on adherence. A novel four-category adherence schema was developed.

[RESULTS] In 13,773 patients, LDCT-only binary adherence (n = 10,237) was 35.6%, 47.8%, and 55.9% at 15, 24, and unlimited months, respectively. Broadening the evaluation to any type of follow-up chest CT (n = 10,436), adherence rose to 45.8%, 59.2%, and 68.4%. Adherence was significantly higher with (1) the 24-month and unlimited time frames compared with 15 months (P < .001) and (2) considering any chest CT versus LDCT only (P < .001). With the four-category schema (n = 13,773), LDCT-only rates were: on time (26.4%), late (15.1%), never followed up (32.7%), and not overdue (25.7%). Including any chest CT, the respective values were 34.7%, 17.1%, 24.0%, and 24.2%.

[INTERPRETATION] This study demonstrates the impact of varying adherence definitions on LCS follow-up rates. Standardized definitions would facilitate program comparison. The proposed four-category schema delineates the screening status of a LCS program's entire cohort.