Respiratory motion of adrenal gland metastases: Analyses using four-dimensional computed tomography images

Purpose: To evaluate the respiratory motion of adrenal gland metastases in three-dimensional directions using four-dimensional computed tomography (4DCT) images.

Methods: From January 2013 to May 2016, 12 patients with adrenal gland metastases were included in this study. They all underwent 4DCT scans to assess respiratory motion of adrenal gland metastases in free breathing state. The 4DCT images were sorted into 10 image series according to the respiratory phase from the end inspiration to the end expiration, and then transferred to FocalSim workstation. All gross tumor volumes (GTVs) of adrenal gland metastases were drawn by a single physician and confirmed by a second. Relative coordinates of adrenal gland metastases were automatically generated to calculate adrenal gland metastases motion in different axial directions.

Results: The average respiratory motion of adrenal gland metastases in left-right (LR), cranial-caudal (CC), anterior-posterior (AP), 3-dimensional (3D) vector directions was 3.4±2.2mm, 9.5±5.5mm, 3.8±2.0mm and 11.3±5.3mm, respectively. The ratios were 58.6%±11.4% and 63.2%±12.5% when the volumes of GTV_In0% and GTV _In100% were compared with volume of IGTV_10phase. The volume ratio of IGTV_10phase to GTV_3D was 1.73±0.48.

Conclusions: Adrenal gland metastasis is a respiration-induced moving target, and an internal target volume boundary should be provided when designing the treatment plan. The CC motion of adrenal gland metastasis is predominant and >5mm, thus motion management strategies are recommended for patients undergoing external radiotherapy for adrenal gland metastasis.