2637 - A Cost-Effective End-to-End Credentialing Test for Simulation-Omitted Direct-to-Unit Adaptive Radiotherapy

Purpose/Objective(s):

Direct-to-Unit (simulation-omitted) adaptive radiotherapy (ART) is an emerging clinical workflow that enables treatment planning directly from diagnostic imaging, eliminating CT simulation and supporting same-day treatment for time-sensitive cases. An independent end-to-end credentialing test prior to clinical implementation is critical to identify workflow defects, systematic inconsistencies, and discrepancies between online ART dose calculations and delivered dose—issues that could otherwise lead to unintended patient’s under- or overdosing. Despite its importance, credentialing end-to-end testing has not been widely adopted for Direct-to-Unit ART, and no IROC credentialing program currently established for these workflows. Although customized ART phantoms are available for this testing, they are expensive and difficult to justify for one-time credentialing use. To address this critical gap, we developed a cost-effective, end-to-end credentialing test using a commercially available phantom, enabling institutions to independently validate Direct-to-Unit ART workflow, thereby enhancing clinical safety.

Materials/Methods:

The credentialing test was performed on a CBCT based ART machine using phantom with interchangeable inserts for A16 ionization chamber point-dose measurements and planar film dosimetry. The A16 chamber and Gafchromic film were independently cross-calibrated on a C-arm Linac against an ADCL-traceable ionization chamber. A pseudo diagnostic-CT digital phantom was created and intentionally deformed to imitate anatomical variability expected in simulation-omitted workflows. Target structures were expanded by 5 mm circumferentially and 1 cm superior–inferior to generate a PTV. A pre-plan was created using an institutional lung prescription of 2 Gy × 30 fractions. Standard ART workflows were followed during the credentialing. Total six fractions were delivered: three scheduled plans and three online adaptive plans generated from CBCTs. Measured point-doses were compared with online-reported values, and film results were assessed with global gamma analysis.

Results:

Point-dose differences at the PTV, spinal cord, and liver were within 3% for both scheduled and adaptive plans. All film measurements exceeded a 94% gamma pass rate using 3%/3 mm, demonstrating strong agreement between planned and delivered dose.

Conclusion:

This study presents a reproducible and cost-effective credentialing framework for Direct-to-Unit ART workflows using widely available commercial equipment. The methodology enables comprehensive verification of online re-optimization and dose delivery accuracy without custom-built phantoms. By providing a scalable pathway for independent validation, this approach supports safe clinical implementation and facilitates broader adoption of simulation-omitted ART while prioritizing patient safety.