Dose verification based on phantom and CT images using Octavius 1500 detector

Abstract

A 3D dose verification of RapidArc plans was performed using an Octavius 1500 detector. The feasibility of 3D dose reconstruction based on CT images and the factors that affect the accuracy of dose reconstruction were investigated. The dose verification results in phantom and CT images were analyzed on 106 clinically approved RapidArc plans for different anatomical sites (31 head and neck, 36 chest, and 39 pelvis), and a 3D global volumetric γ index analysis was established under the tolerance criteria of 3%/3 mm, 3%/2 mm, 2%/2 mm, and 2%/1 mm (threshold 10%). The average volumetric 3D global gamma analysis results for the different sites were 99.31%, 99.86%, and 98.36% (3%/3 mm, p=0.308) and 96.74%, 97.91%, and 95.16% (3%/2 mm, p=0.193). For the 36 plans measured with the Octavius 729 matrix again, the 95% confidence intervals for the 1500 and 729 detectors were [98.53, 99.58]% and [95.16, 96.93]% for the 3%/3 mm criteria (mean values are 99.05% and 96.05%), [95.57, 97.99]% and [89.56, 92.63]% for the 3%/2 mm criteria (mean values are 96.78% and 91.09%), [88.89, 94.10]% and [81.41, 86.09]% for the 2%/2 mm criteria (mean values are 91.49% and 83.75%), and [75.66, 84.14]% and [67.68,74.05]% for 2%/1 mm criteria (mean values are 79.9% and 70.86%), respectively. The accuracy of the Octavius system in reconstructing the 3D volumetric dose may depend on the complexity of the target, the steepness of the dose gradient, and the resolution of the ionization chamber matrix. Analysis of the failed points (γ>1) based on the plan CT images is feasible.

Keywords

• octavius 1500 ion chamber detector
• rapidarc
• 3d dose reconstruction
• quality assurance