Quantifying road infrastructure vulnerability for radiotherapy access in Luzon, Philippines

Purpose: Radiotherapy (RT) requires strict adherence to daily treatment fractionation, making reliable physical access to treatment centers a critical determinant of clinical outcomes. While recent geospatial catchment models have quantified regional access disparities, they often assume uniform travel and ignore the physical vulnerability of the actual road infrastructure. This study investigates the infrastructural fragility of RT access in Luzon, hypothesizing that realistic patient transit heavily depends on a few highly centralized, vulnerable road networks. Methods: A computational routing model of Luzon’s road network was constructed using OpenStreetMap data. Origin points representing 600 municipalities in Luzon, weighted by local RT demand, were routed to the 43 existing RT centers. To identify network vulnerabilities, we calculated demand-weighted subset edge betweenness centrality (SEBC) to quantify the total volume of patient demand passing through any specific road segment. We compared two transit scenarios: a theoretical shortest-distance baseline and a realistic fastest-time travel. Results: Minimizing travel time induced a severe structural reorganization of the access network. Under distance-based routing, the transit burden was distributed across a redundant grid of trunk and primary roads. Conversely, realistic time-based routing aggressively consolidated this burden onto the expressway network, surging its network share from 22.8% to 52.6%. The Skyway, NLEX, SCTEX, and SLEX corridors emerged as the maximum SEBC links. This reliance creates a critical clinical bottleneck, identifying exactly where the national access network is most vulnerable to localized infrastructure failures, such as severe flooding or network disruptions. Conclusion: By quantifying actual patient transit pathways rather than mere geographic proximity, this study reveals the vulnerability of Luzon’s road network for radiotherapy access. These findings offer data-driven infrastructure insights for the implementation of the National Integrated Cancer Control Act (NICCA), demonstrating that future LINAC installations must be strategically placed to decentralize this transit burden and ensure a resilient, equitable cancer care network.