Optimizing patient access: feasibility of a direct-to-unit proton therapy workflow using the online adaptive workflow

The current clinical workflow in radiation therapy relies on the patient undergoing a planning CT weeks prior to the first treatment fraction. This leads to delays in the start of treatment, poses an additional burden on the patient, and increases the environmental impact. Recent studies show that a direct-to-unit (DTU) workflow, which skips the planning computed tomography (CT), is feasible in photon therapy. This study aims to investigate the feasibility of a DTU workflow in proton therapy (PT) using adaptive techniques, allowing reoptimization on a new CT. We retrospectively analyzed 9 cases with diagnostic images (CT or magnetic resonance imaging (MRI)) acquired between 6 days and 19 months prior to the planning CT. When only MRI was available, synthetic CTs (sCTs) were generated. The treatment plan (diagnostic plan) was created on the diagnostic image and optimized to meet the clinical goals. The reoptimization of the diagnostic plan on the planning CT generated the DTU plan. We compared the DTU plan with the plan independently created on the planning CT (clinical plan) by focusing on target coverage, organ at risk (OAR) sparing, clinical goals satisfaction, and robustness to uncertainties. All DTU plans either met the clinical goals or deviated by less than 5% of prescribed dose/volume, except for 5 target minimum dose endpoints. For OARs, 92% of the goals were fulfilled, and 82% of OAR goal metrics stayed below +5% deviation from the clinical plan. Deviations in the target D98%(dose received by 98% of the volume), mean dose, and V95% (volume of the target receiving at least 95% of the prescribed dose) between DTU and clinical plans showed medians of -0.71%, 0.43%, and -0.10%. Evaluation of plan robustness showed no relevant differences. In this study, we demonstrated the feasibility of a DTU workflow for PT using an adaptive framework. If implemented, DTU would save time, reduce the travel burden on the patient, and positively impact the environment.