Clinical Evaluation of Adaptive Radiotherapy In Radixact x9 for Precision and Raystation Due to Hounsfield Unit Variations
Abstract
Purpose
To evaluate the impact of density models on dose calculation in the RayStation and Precision treatment planning systems, using images acquired with the Radixact X9 (Accuray Inc., Sunnyvale, CA).
Methods
Images were acquired while varying the acquisition parameters (kVp, mAs, FOV, beam width, couch speed, and number of views per rotation) using a TomoPhantom-HE “Cheese Phantom” (homogeneous medium) and an anthropomorphic phantom (heterogeneous medium). The resulting Hounsfield unit (HU) values were compared with those obtained using a reference protocol, Thorax Large 440 mm Fine (120 kVp, 480 mAs, FOV 440 mm, slice interval 1.8 mm, slice thickness 3.6 mm), through statistical significance tests. Subsequently, doses calculated for each protocol were compared using regions of interest (ROI) and dose distributions by means of gamma analysis (DTA, %DD, and γ criteria). Finally, dose delivery was verified using A1SL ionization chambers (Standard Imaging, Middleton, WI).
Results
A statistically significant variation in HU values was observed in 14 protocols (p < 0.05) when modifying the acquisition parameters. The analyses showed differences < 1% in both Precision and RayStation with respect to the dose calculated using the reference protocol within the ROIs. Dose verification demonstrated differences < 1% in the homogeneous medium and < 3% in the heterogeneous medium for both treatment planning systems.
Conclusion
The results suggest the need for standardization of image acquisition protocols (density models) that exhibit statistically significant differences, since variations in acquisition parameters may alter the HU–density correspondence. Nevertheless, the verifications demonstrated that the density models implemented in RayStation® and Precision® compensate for these variations, showing agreement with the clinical guidelines of the AAPM Task Group (TG) 65. Consequently, the applicability of adaptive radiotherapy (ART) on the Radixact X9 is validated.