Extended localization and adaptive dose calculation using HU corrected cone beam CT: Phantom study

Area of Science:

• Medical Physics
• Radiotherapy
• Image-guided radiation therapy (IGRT)

Background:

• Cone beam CT (CBCT) is crucial for dose calculation in radiotherapy.
• Standard CBCT scanning length is often insufficient for comprehensive patient localization.
• Adaptive dose calculation strategies are needed to address anatomical changes during treatment.

Purpose of the Study:

• To explore extended tomographic localization using stitched CBCT image sets.
• To investigate adaptive dose calculation strategies with Hounsfield unit (HU) corrected CBCT.
• To assess the feasibility of routine adaptive re-planning using enhanced CBCT techniques.

Main Methods:

• Developed two stitching strategies ('penumbral-overlap' S1 and 'no-overlap' S2) for extended CBCT localization.
• Implemented a local HU-correction technique using MATLAB scripts.
• Mapped fluence modulated treatment plans from planning CT (pCT) to stitched CBCT and performed dosimetric analyses (dose profile, 3D-gamma evaluation, DVH comparison).

Main Results:

• Extended CBCT scanning length by up to 15 cm (S1) and 16 cm (S2).
• Observed minor variations in delineated structures and beam coordinates (max -1.6% volume change, max 2.7 mm positional difference).
• Achieved high gamma evaluation pass-rates (≥98.5% for 3%/3 mm and 2%/2 mm criteria), indicating desirable dosimetric accuracy.

Conclusions:

• Developed cone beam tomographic stitching and local HU-correction strategies enhance localization and dose calculation.
• These strategies facilitate routine adaptive re-planning in radiotherapy.
• The method circumvents the need for repeated planning CT scans, improving workflow efficiency.