# Geographic access to radiotherapy facilities in Japan

## TL;DR

This study maps how far Japanese patients must travel for different types of radiotherapy, showing that advanced treatments are harder to access in rural and mountainous areas.

## Contribution

The study introduces a novel nationwide, modality-specific assessment of geographic access to radiotherapy in Japan.

## Key findings

- Median travel time for EBRT is 6.48 minutes, but increases to 14.06 minutes for brachytherapy.
- 0.48% of the population faces travel times ≥120 minutes for brachytherapy, double that of EBRT.
- Mountainous and island regions show 'newly poor-access' areas when advanced radiotherapy is required.

## Abstract

Daily attendance requirements for radiotherapy (RT) make geographic accessibility a critical determinant of treatment adherence and completion. Although facility surveys indicate that advanced modalities such as intensity-modulated radiotherapy (IMRT) and brachytherapy are concentrated in urban centers, precise nationwide quantification of the resulting patient travel burden remains lacking. This study provides the first nationwide, modality-stratified assessment of geographic access to RT in Japan. Using the Open Source Routing Machine and a high-resolution dataset of 176 964 household-weighted 1-km mesh centroids, we calculated driving times to the nearest external-beam radiotherapy (EBRT), IMRT and brachytherapy facilities. Beyond standard distribution metrics, we generated high-resolution ‘penalty maps’ to quantify the incremental time tax imposed by advanced modality requirements. Although EBRT access was uniformly short nationwide, with a median travel time of 6.48 min, this increased to 8.26 min for IMRT and 14.06 min for brachytherapy. Crucially, the proportion of the population facing poor access (≥120 min) doubled from 0.24% for EBRT to 0.48% for brachytherapy. The spatial analysis identified specific ‘newly poor-access’ areas—regions that are accessible for EBRT but become remote when advanced care is needed—forming coherent geographic clusters in mountainous and island zones. These findings demonstrate that modality requirements introduce meaningful inequities despite strong national EBRT infrastructure. These indicators provide a vital evidence base for spatially optimizing resources to mitigate travel burdens for Japan’s aging, mobility-limited population.