Daytime Idle Energy Reduction in Radiotherapy Simulation Computed Tomography: A Prospective Workflow-Based Evaluation

Previous computed tomography (CT) energy-saving studies have primarily focused on after-hours shutdown or idle energy use in diagnostic CT. Radiotherapy simulation, however, includes preparation and immobilisation steps that may prolong daytime non-acquisition periods. This study quantified daytime energy use in radiotherapy simulation CT and evaluated the contribution of power-saving operation.

In this prospective single-centre study, electrical power consumption was directly measured using a three-phase power logger during five baseline and five power-saving weekdays (08:00-18:00). Power measurements were integrated with patient in-room intervals and simulation procedure categories. Staff perceptions of workflow impact were assessed using an anonymous questionnaire, and carbon implications were estimated from the measured energy reduction.

Mean directly measured clinical-hour energy consumption decreased from 38.7 to 36.5 kWh/day with power-saving operation, a 5.8% reduction. Non-acquisition time during patient presence varied markedly by procedure, from 56.5% for respiratory-gated four-dimensional CT to 97.1% for head-and-neck simulation. Power-saving operation shifted daytime power use towards a lower-power state, corresponding to an estimated reduction of 0.84-1.01 kg-CO₂ per clinical day across the emission-factor sensitivity range. Twenty of 21 staff (95.2%) reported no impact on patient throughput.

Power-saving operation reduced daytime energy consumption without meaningful workflow disruption. Radiotherapy simulation CT has prolonged, procedure-dependent idle periods arising from radiotherapy-specific preparation workflows, highlighting a practical and previously undercharacterised opportunity for energy reduction.