Factors Influencing the Timeliness and Completeness of Appropriate Staging Investigations for Patients with Stage I–III Lung Cancer in Southeastern Ontario

(1) Background: Comprehensive and timely lung cancer (LC) staging is essential for prognosis and management. The Lung Diagnostic Assessment Program (LDAP) in Southeastern (SE) Ontario aims to provide rapid, guideline-concordant care for suspected LC patients. We evaluated factors affecting the completeness and timeliness of staging for stage I-III LC patients in SE Ontario, including the impact of LDAP management. (2) Methods: This was a population-based retrospective cohort study using the LDAP database (January 2017-December 2019), linked with the Ontario Cancer Registry, to identify newly diagnosed LC patients. A Cox model approach identified variables associated with staging completeness and timeliness. (3) Results: Among 755 patients, 459 (60.8%) were managed through LDAP. Optimal staging was achieved in 596 patients (78.9%), 23 (3.0%) had alternative staging, and 136 (18.0%) had incomplete staging. In the adjusted analyses, LDAP management was associated with a higher likelihood of complete staging (OR 2.29, <i>p</i> < 0.0001) and faster staging completion (β = -18.53, <i>p</i> < 0.0001). Increased distance to PET centres was associated with a longer time to complete staging (β = 8.95 per 100 km, <i>p</i> = 0.0007), as was longer time to diagnosis (β = 21.63 per 30 days, <i>p</i> < 0.0001). (4) Conclusions: LDAP management in SE Ontario significantly improved staging completeness and shortened staging time for stage I-III LC patients.