Dosimetric study of the deformable image registration based lung cancer adaptive radiotherapy

The purpose of this study is to evaluate the dosimetric gain of the adaptive radiotherapy (ART) over conventional intensity modulated radiation therapy (IMRT) by using as the deformable image registration technique for dose mapping and summation to assess the dosimetric difference on target and organs at risk (OARs) dose. We retrospectively collected planning CT images and fractional CT images from nine lung cancer patients who were treated with adaptive IMRT. During fractional treatments, new tumor and organ contours are generated using the deformable image registration and a new IMRT plan is generated for the follow up treatments for each patient. The resulting deformation moving vector fields are also used to map and accumulate dose from the first 20 fractions to the sequential 10 fractions for final total dose calculation. The organs at risk (OARs) and the tumor of dosimetric parameters are compared between the ART and conventional IMRT plan. The evaluation results showed that when using the ART technique, the mean GTV volume is reduced by 53.2%, the mean tumor dose is increased by 0.41Gy, the mean lung V20 and V30 are decreased by 2.17% and 3.32%, the mean heart V30 and V40 are decreased by 1.14% and 2.98%, respectively, and the maximum dose of spinal cord is decreased by 1.21Gy when compared with the conventional IMRT. This work demonstrated the feasibility of ART to achieve better target coverage and OARs sparing over the conventional IMRT, and it will potentially reduce the radiation side effect and increase the local control rate.