Development of a cost-effective end-to-end commissioning test for simulation-omitted direct-to-unit adaptive radiotherapy

Background and purpose Direct-to-Unit (simulation-omitted) adaptive radiotherapy (ART) enables same-day treatment by generating treatment plans from diagnostic images, eliminating the need for computed tomography (CT) simulation. These workflows rely on online plan re-optimization to account for anatomical, CT-number, and setup variations. However, no standardized end-to-end (E2E) credentialing protocol currently exists to validate the accuracy of Direct-to-Unit ART. Although customized ART phantoms are available, they are often costly, and impractical for one-time commissioning. To address this gap, we developed a low-cost E2E commissioning framework using a commercially available CIRS ZEUS phantom to verify workflow accuracy while minimizing financial burden.Materials and methods E2E commissioning tests were performed on Varian Ethos and Elekta Unity systems using a CIRS ZEUS phantom (Model 008Z) equipped with inserts for ionization chamber point-dose and planar film measurements. The ionization chamber and Gafchromic EBT4 films were independently cross-calibrated on an Elekta Versa linear accelerator. Pseudo-diagnostic CT datasets were generated and deformed to simulate anatomical variation. Pre-plans (2 Gy × 30 fractions) were created and delivered across three ART fractionation schemes. Point-dose measurements were compared with system-reported values, and planar dose distributions were evaluated using global gamma analysis.Results All point-dose differences were within 3% (for high-dose regions) or 3 cGy (for low-dose regions) of the system-reported values. All planar film measurements achieved gamma pass rates exceeding 90% using 3%/3 mm criterion.Conclusion This cost-effective E2E approach provides a practical commissioning solution for Direct-to-Unit ART, supporting safe clinical implementation and facilitating cross-institutional standardization.