Effect of tumor amplitude and frequency on 4D modeling of Vero4DRT system

Abstract

Background

An important issue in indirect dynamic tumor tracking with the Vero4DRT system is the accuracy of the model predictions of the internal target position based on surrogate infrared (IR) marker measurement. We investigated the predictive uncertainty of 4D modeling using an external IR marker, focusing on the effect of the target and surrogate amplitudes and periods.

Methods

A programmable respiratory motion table was used to simulate breathing induced organ motion. Sinusoidal motion sequences were produced by a dynamic phantom with different amplitudes and periods. To investigate the 4D modeling error, the following amplitudes (peak-to-peak: 10–40[[ce:hsp sp="0.25"/]]mm) and periods (2–8[[ce:hsp sp="0.25"/]]s) were considered. The 95th percentile 4D modeling error (4D-E_95%) between the detected and predicted target position (μ[[ce:hsp sp="0.25"/]]+[[ce:hsp sp="0.25"/]]2SD) was calculated to investigate the 4D modeling error.

Results

4D-E_95% was linearly related to the target motion amplitude with a coefficient of determination R²[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.99 and ranged from 0.21 to 0.88[[ce:hsp sp="0.25"/]]mm. The 4D modeling error ranged from 1.49 to 0.14[[ce:hsp sp="0.25"/]]mm and gradually decreased with increasing target motion period.

Conclusions

We analyzed the predictive error in 4D modeling and the error due to the amplitude and period of target. 4D modeling error substantially increased with increasing amplitude and decreasing period of the target motion.