3D dose verification using tomotherapy CT detector array.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Accurate dose verification is crucial in stereotactic body radiation therapy (SBRT).
• Tomotherapy utilizes an onboard detector for potential real-time dose monitoring.
• Evaluating novel verification methods is essential for improving treatment safety and efficacy.

Purpose of the Study:

• To assess a novel three-dimensional (3D) dose verification technique.
• The method is based on measuring the exit dose using tomotherapy's onboard detector.
• This evaluation aims to confirm its accuracy in clinical settings.

Main Methods:

• The study analyzed 347 treatment fractions from 24 patients across prostate, head and neck (HN), and spinal SBRT cases.
• Detector sonograms were back-projected to determine entrance fluence.
• This fluence was then forward-projected onto CT images to compute the verification dose.

Main Results:

• Excellent agreement was found between calculated doses and ion chamber measurements (RMS errors ~2%).
• For HN patients, the mean dose to the planning target volume (PTV) had an RMS error of 3.55%.
• Dose agreements for PTVs and organs at risk were within 5% for cumulative doses in most patient treatments.

Conclusions:

• The exit dose-based 3D dose verification method demonstrates high accuracy.
• The technique provides reliable dose assessment for SBRT treatments.
• Dosimetric error is sensitive to multileaf collimator leaf timing and gantry rotation speed.