Poster — Thur Eve — 35: Lung SBRT: 4DCT Based Treatment Planning in Presence of Respiratory Motion

Abstract

The purpose of this study was to determine the impact of internal target volume (ITV) density on the 4DCT based lung stereotactic body radiotherapy (SBRT) treatment planning (TP) using the ITV density assignment correction (DAC). Siemens 40‐slice CT scanner was used to acquire 8 phases of 4DCT images and a free breathing CT scan of CIRS Dynamic Thorax Phantom with the tumor moving in three dimensions. The ITV was created from the merge of all the CTVs in all the phases in Eclipse and copied to the free breathing CT scan for planning dose calculation. The PTV was created by adding a 5mm margin around the ITV. Lung SBRT plans were created using the 0% inhale phase, the 50% inhale phase and the free breathing CT scan under the original CT scan and DAC in the ITV. Our data shows ITV coverage from the isodose line, DVH analysis and mean dose on the free breathing CT scan, 0% inhale phase and 50% inhale phase with and without ITV DAC. The high dose region follows the CTV without DAC in the ITV because of the higher build‐up of dose within the denser CTV volume than in the surrounding less dense lung tissue. The MU decreased 0.9%, 1.3% and 1.2% for free breathing scan, 0% inhale and 50% inhale respectively with DAC in the ITV. The DAC provided a clinical acceptable way to predict the ITV dose coverage in the treatment planning system.