Evaluation of a novel CBCT conversion method implemented in a treatment planning system

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Cone-beam computed tomography (CBCT) is crucial for image-guided radiation therapy.
• Accurate dose calculation in CBCT is essential for effective cancer treatment.
• Novel algorithms are needed to improve CBCT-based dose calculations.

Purpose of the Study:

• To evaluate a novel CBCT conversion algorithm for dose calculation.
• To compare its performance against a bulk density overriding technique.
• To assess the impact of anatomical variations on dose distribution.

Main Methods:

• Implemented a new CBCT conversion algorithm (CBCTc) in a research treatment planning system.
• Collected CBCT data from head and neck, gynecology, and lung cancer patients.
• Compared CBCTc with a bulk density overriding method (CBCTb) and deformed CT (dCT) using gamma analysis.

Main Results:

• The CBCTc method demonstrated systematically higher gamma pass rates (GPRs) than the CBCTb method.
• Median GPRs for CBCTc were 100% (HN), 99.8% (GYN), and 99.9% (LNG).
• Significant differences were observed, particularly near air/tissue interfaces due to anatomical variations.

Conclusions:

• The novel CBCTc algorithm provides excellent agreement with dose calculations on planning CT (pCT) and deformed CT (dCT).
• CBCTc significantly outperforms the CBCTb method in dose distribution accuracy.
• Anatomical variations remain a key factor influencing dose calculation deviations.