Abstract
BACKGROUND: To investigate how the four-dimensional computed tomography (4DCT) technique spares normal tissues in non-small cell lung cancer (NSCLC) radiotherapy by defining individualized internal target volume (ITV). MATERIALS AND METHODS: Gross tumor volume (GTV) and clinical target volume (CTV) were contoured on all 10 respiratory phases of 4DCT scans in 10 patients with peripheral NSCLC. Both 3D and 4D treatment plans were performed for each patient using planning target volume (PTV)3D (derived from a single CTV plus conventional margins) and PTV4D (derived from 4D internal target volume, which included all 10 CTVs plus setup margins). Dose volume histogram and normal tissue complication probability (NTCP) values were compared for the lung, heart, and spinal cord between 3D and 4D treatment plans. RESULTS: The average PTV of the 4D (127.56 ± 70.79) was less than the 3D plans (147.65 ± 76.89). The 4D spared more surrounding normal tissues than the 3D plans, especially in the lung. Compared with 3D plans, V5, V10, V20 and V30 of the total lung decreased from 41.25%, 37.75%, 24.25%, 17.00% to 38.13%, 33.00%, 21.25%, 15.13%, respectively. Without increasing the NTCP of the lung significantly, the 4D plans allowed us to increase the average prescription dose from 60 Gy to 66.00 ± 4.62 Gy. CONCLUSIONS: 4DCT based plans can reduce the target volumes, spare more normal tissues, and allow dose escalation compared with 3D plans in NSCLC radiotherapy.