TomoTherapy MLC verification using exit detector data.

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Intensity-modulated radiation therapy (IMRT) requires precise delivery verification (DV) for optimal patient outcomes.
• Image-guided radiation therapy (IGRT) and IMRT allow for conformal plans and tighter margins, but errors can be detrimental.
• TomoTherapy's multileaf collimator (MLC) performance verification is crucial for treatment accuracy.

Purpose of the Study:

• To develop a novel DV technique for TomoTherapy's MLC using onboard mega-voltage CT (MVCT) detectors.
• To verify the accuracy and robustness of the developed DV technique under various conditions.
• To identify the root cause of failures in clinical plans that did not pass delivery quality assurance (DQA).

Main Methods:

• Utilized temporal changes in MVCT detector signals to predict actual MLC leaf open times.
• Applied an iterative Richardson-Lucy (R-L) deconvolution algorithm to mitigate penumbra and scattered radiation effects.
• Verified the DV technique using optical sensors on MLC leaves and introduced attenuation materials to test robustness.

Main Results:

• The DV technique accurately estimated MLC leaf open times, agreeing with optical sensors within 0.2 ms (99% within 8.5 ms).
• Results remained consistent even with added beam attenuation.
• Successfully identified MLC timing discrepancies as the cause of DQA failures in clinical plans, with reconstructed doses agreeing within 1% of measured doses.

Conclusions:

• TomoTherapy exit detectors provide valuable data for monitoring MLC behavior during radiation delivery.
• A robust and accurate DV technique was developed to estimate MLC leaf open times from exit detector signals.
• This method enhances the verification of radiation therapy delivery, improving treatment safety and efficacy.