Assessment of CBCT Post-Processing Algorithms for Head and Neck Adaptive Radiotherapy: A Cautionary Note on Dosimetric and Anatomical Accuracy
Abstract
Purpose
To evaluate the dosimetric and anatomical accuracy of RayStation-generated corrected cone-beam CT (cCBCT) and virtual CT (vCT) for adaptive radiotherapy (ART) in head and neck (H&N) cancer patients with significant anatomical change.
Methods
For 10 H&N patients who underwent resimulation due to significant anatomical changes in our clinic, we analyzed cCBCT and vCT generated from the original planning CT in conjunction with the daily CBCT acquired closest in time to a repeat simulation (resim CT). The cCBCT, vCT, and the corresponding resim CT for each patient were compared. Evaluations included quantitative analysis of CT number Hounsfield unit (HU) accuracy and 3D dosimetric comparisons of the same resim treatment plan calculated on each dataset. Anatomical fidelity was also assessed visually.
Results
Contrary to findings in other anatomical sites, both cCBCT and vCT demonstrated significantly different CT number distributions (HU mean absolute error: 200±44 HU, 222±102 HU) and resultant dose distributions compared to the reference resim CT (gamma index: 2%/2mm, 89.2±7.9%, 91.7±5.1%) in these H&N cases. The vCT, in particular, was prone to visible and substantial anatomical discrepancies that did not faithfully represent the patient’s true geometry at resimulation. These inaccuracies translated into significant dosimetric deviations.
Conclusion
For H&N cancer patients, especially those experiencing rapid anatomical changes, neither cCBCT nor vCT from RayStation in their current state provide sufficient anatomical or dosimetric accuracy to serve as a standalone dataset for generating a new adaptive treatment plan. Their role should be limited to an initial evaluation tool to trigger the decision for adaptive intervention. Once ART is deemed necessary, a new full-quality simulation CT scan remains essential for accurate replanning to ensure safe and precise dose delivery. This highlights the site-specific challenges of CBCT-guided ART and underscores the need for continued algorithm refinement and validation for complex H&N anatomy.