4D modeling in a gimbaled linear accelerator by using gold anchor markers

Abstract

Purpose

The purpose of this study was to verify whether the dynamic tumor tracking (DTT) feature of a Vero4DRT system performs with 10-mm-long and 0.28[[ce:hsp sp="0.25"/]]mm diameter gold anchor markers.

Methods

Gold anchor markers with a length of 10[[ce:hsp sp="0.25"/]]mm and a diameter of 0.28[[ce:hsp sp="0.25"/]]mm were used. Gold anchor markers were injected with short and long types into bolus material. These markers were sandwiched by a Tough Water (TW) phantom in the bolus material. For the investigation of 4-dimensional (4D) modeling feasibility under various phantom thicknesses, the TW phantom was added at 2[[ce:hsp sp="0.25"/]]cm intervals (in upper and lower each by 1[[ce:hsp sp="0.25"/]]cm). A programmable respiratory motion table was used to simulate breathing-induced organ motion, with an amplitude of 30[[ce:hsp sp="0.25"/]]mm and a breathing cycle of 3[[ce:hsp sp="0.25"/]]s. X-ray imaging parameters of 80[[ce:hsp sp="0.25"/]]kV and 125[[ce:hsp sp="0.25"/]]kV (320[[ce:hsp sp="0.25"/]]mA and 5[[ce:hsp sp="0.25"/]]ms) were used. The least detection error of the fiducial marker was defined as the 4D-modeling limitation.

Results

The 4D modeling process was attempted using short and long marker types and its limitation with the short and long types was with phantom thicknesses of 6 and 10[[ce:hsp sp="0.25"/]]cm at 80[[ce:hsp sp="0.25"/]]kV and 125[[ce:hsp sp="0.25"/]]kV, respectively. However, the loss in detectability of the gold anchor because of 4D-modeling errors was found to be approximately 6% (2/31) with a phantom thickness of 2[[ce:hsp sp="0.25"/]]cm under 125[[ce:hsp sp="0.25"/]]kV. 4D-modeling could be performed except under the described conditions.

Conclusions

This work showed that a 10-mm-long gold anchor marker in short and long types can be used with DTT for short water equivalent path length site, such as lung cancer patients, in the Vero4DRT system.