Application of a linear interpolation algorithm in radiation therapy dosimetry for 3D dose point acquisition

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Air-vented ion chambers offer precision in radiation therapy dosimetry.
• Ion chamber detector arrays often lack sufficient spatial sampling for accurate volumetric dose reconstruction.
• Interpolation algorithms are explored to overcome sampling limitations.

Purpose of the Study:

• To investigate the linear interpolation algorithm for volumetric dose reconstruction in Volumetric Modulated Arc Therapy (VMAT).
• To evaluate the impact of ion chamber spacing and anatomical mass density on interpolation accuracy.
• To assess dosimetric differences between treatment planning and reconstructed doses.

Main Methods:

• Acquired plane measurement doses from 83 VMAT plans using Octavius 729, Octavius1500, and MatriXX ion chamber arrays.
• Applied linear interpolation to reconstruct volumetric doses from measured data.
• Evaluated dose-volume histogram metrics for planning target volumes (PTVs) and organs at risk (OARs).

Main Results:

• Dose deviations in PTVs varied: Dmean ranged from 1.5-7.3%, Dmax ranged from 1.6-7.6% depending on the array.
• Average dose/volume deviations for PTVs and OARs were site-dependent, with larger deviations in mediastinum/lung plans (up to 8.9%).
• Smaller detector spacing and higher detector density correlated with reduced interpolation error; lower mass density inhomogeneity improved accuracy.

Conclusions:

• Linear interpolation accuracy is influenced by detector spacing, density, and anatomical variations.
• The performance of linear interpolation in VMAT dosimetry is limited by these factors.
• Alternative interpolation methods are recommended for improved radiotherapy dosimetry accuracy.