Author: Theodore Higgins Arsenault, Kenneth W. Gregg, Lauren E Henke, Rojano Kashani, Alex T. Price, Sagar Regmi, Atefeh Rezaei, Runyon C. Woods 👨🔬
Affiliation: University Hospitals Seidman Cancer Center 🌍
Purpose: To investigate the feasibility and accuracy of using a Hounsfield Unit(HU) calibrated cone-beam computed tomography(CBCT) for direct dose calculation in thoracic treatment settings. In combination with patient motion, the increased low-density tissue and tissue heterogeneities within the thoracic region may increase uncertainties in dose calculation. Therefore, we aim to assess dose calculation accuracy using dose-volume histogram metrics(DVHM) and gamma-analysis.
Methods: Five patients with thoracic malignancies were imaged on a CT simulator and a HyperSight imaging CBCT solution with calibrated HU values available on the TrueBeam linac. Clinical treatment plans were generated for each patient on the CT simulator scan(CTplan). Each plan was copied and recalculated on a CBCT dataset matching the motion management strategy chosen at simulation(CBCTplan). DVHMs evaluated were the internal gross tumor volume(iGTV) and planning target volume(PTV) D98%Vol, D50%Vol, and D2%Vol. The lung-iGTV mean dose along the longitudinal extent of the PTV was also evaluated. The acceptable range of the DVHM percent difference was 5%. Gamma analysis was also performed between the dose distributions with testing parameters of 2%/2mm, local normalization, and thresholds of 10% with a passing score greater than 90%.
Results: The median(min-max) difference(CTplan-CBCTplan) for each target DVHM was: iGTV D98%Vol(0.5%: -2.0% to 2.8%), D50%Vol(0.3%: -2.2% to 1.9%), D2%Vol(0.4%: -4.1% to 1.1% ); PTV D98%Vol (1.0%: -1.8 to 7.0%), D50%Vol (0.6%: -2.3% to 3.4%), D2% (0.4%: -3.9% to 1.1%). The isolated lungs-iGTV Dmean and D50 median dose difference was 0.2% (-1.5% to 3.4%) and 0.1%(-2% to 3.8%) respectively. 34/35 DVHMs met our passing criteria, which were set at a 5% difference. The median gamma results were 96.5% (93.8% to 99.7%), and 5/5 met the passing criteria.
Conclusion: Accurate thoracic dose calculation using C-arm-based CBCTs enhances treatment precision and streamlines adaptive radiotherapy workflows, ultimately leading to improvement in patient care and clinical efficiency.