3D dose reconstruction of pretreatment verification plans using multiple 2D planes from the OCTAVIUS/Seven29 phantom...

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate 3D dose reconstruction is crucial for patient-specific quality assurance (QA) in radiation therapy.
• Pretreatment verification of Volumetric Modulated Arc Therapy (VMAT) plans ensures treatment accuracy.
• Evaluating novel reconstruction methods is essential for advancing QA technologies.

Purpose of the Study:

• To assess the accuracy of a 3D dose reconstruction technique using multiple 2D planar dose measurements.
• To evaluate the performance of a cylindrical geometry-based linear interpolation method for VMAT QA.
• To compare reconstructed 3D doses with treatment planning system (TPS) calculated doses.

Main Methods:

• Eight VMAT patient treatment plans were delivered to an OCTAVIUS phantom with a Seven29 detector array.
• The phantom was rotated in 45° increments, and planar doses were acquired and analyzed using MATLAB.
• A cylindrical geometry-based linear interpolation method was employed for 3D dose reconstruction and compared to TPS calculations.

Main Results:

• The 3D dose reconstruction showed good agreement (<2%) in high-dose regions but discrepancies in low-dose regions.
• Agreement was good for sagittal and coronal planes, with slight discrepancies in the transverse plane.
• 3D gamma analysis yielded an average passing rate of 92.4% (5%/5 mm) and 80.1% (2%/2 mm).

Conclusions:

• A simple cylindrical geometry-based linear interpolation method can achieve good agreement for 3D dose reconstruction in high-dose regions.
• The interpolation method introduces discrepancies in regions of high dose gradients.
• This study provides a benchmark for 3D dose delivery QA using current technology and highlights areas for algorithmic improvement.