Regional disparities in IMRT utilization in Japan: analysis of trends and associated medical resources from 2015 to 2019†.

Intensity-modulated radiation therapy (IMRT) uses intensity-modulated photon beams from multiple directions to achieve conformal dose delivery to a target with a complex shape while reducing the dose to organs at risk. We analyzed the trends in IMRT utilization rates across Japanese prefectures from 2015 to 2019 and investigated their relationship with medical resources. Data from the National Database of Health Insurance Claims and the Japanese Society for Radiation Oncology Structure Survey were analyzed. IMRT utilization rates and medical resources (radiation oncologists, medical physicists, radiation technologists, and IMRT-capable linear accelerators) were assessed for all 47 prefectures. A mixed-model analysis was employed to examine the relationship between IMRT utilization rates and medical resources. IMRT utilization increased from 16.4% in 2015 to 22.0% in 2019, with significant regional disparities (range, <10% to >30%). Mixed-model analysis revealed that the number of IMRT-capable linear accelerators (estimate = 0.073, P < 0.01) and radiation oncologists (estimate = 0.032, P = 0.04) was significantly associated with higher IMRT utilization rates. Medical physicists and radiation technologists showed no significant association with IMRT utilization rates. Although the use of IMRT has increased in Japan, substantial regional disparities persist. Increasing the number of IMRT-capable linear accelerators and radiation oncologists may be the most effective strategy to improve equitable access to IMRT in Japan.