An evaluation of techniques for dose calculation on cone beam computed tomography

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Science

Background:

• Cone beam CT (CBCT) is increasingly used in radiotherapy for treatment verification and adaptive planning.
• Accurate dose recalculation on CBCT images is crucial for ensuring treatment efficacy and patient safety.
• Evaluating different dose reconstruction methods is essential for optimizing radiotherapy workflows.

Purpose of the Study:

• To compare the accuracy and efficiency of four dose recalculation techniques on CBCT images.
• To identify the optimal method for dose recalculation in radiotherapy treatments using CBCT.
• To provide data for clinical radiotherapy departments to improve dose representation.

Main Methods:

• Investigated four techniques: standard planning CT (pCT) calibration curve, CBCT site-specific calibration curve, density override, and deformable registration.
• Applied techniques to 15 patients undergoing volumetric modulated arc therapy (VMAT) for head and neck, lung, or prostate cancer.
• Assessed accuracy using dose volume histogram (DVH) metrics and 2.0%/0.1 mm gamma analysis against pCT dose distribution.

Main Results:

• All techniques showed minimal differences (0.0-2.3%) in DVH metrics for target volumes and organs at risk.
• Deformable registration achieved the highest volumetric gamma analysis pass-rates across all treatment sites.
• Median gamma pass-rates at 50% threshold ranged from 94.6% to 99.9% depending on the technique and treatment site.

Conclusions:

• Deformable registration, HU override, and site-specific calibration curves are dosimetrically accurate and efficient for CBCT dose calculation.
• These methods enable more accurate patient treatment representation in image-guided and adaptive radiotherapy.
• The findings support clinical implementation for improved radiotherapy planning and delivery.