Concurrent chemotherapy and 3-dimensional conformal radiation therapy (3D-CRT), using computed-tomography (CT) simulation, is the current standard approach in the treatment of inoperable non-small-cell lung cancer (NSCLC). Despite such therapeutic benefit, local recurrence nonetheless remains a significant impediment to cure. Attempts to improve the accuracy of CT-scanning in radiotherapy treatment planning have been increasingly studied. One such approach is the attempted correlation of CT imaging temporally with the physiologic breathing cycle, a process known as gating. By imaging the tumor only when the tumor is immobilized, gating effectively eliminates the effect of motion, thus leading to typically smaller visible tumor masses and the loss of motion-induced distortions. Lung-tumor immobilization using self-gated breath-holding at extremes of inspiration has been validated clinically, and is associated with improved lung-outcome predictors and normal tissue complication probability overall. Several recent studies have demonstrated PET to be both highly sensitive and moderately to highly specific in the staging of NSCLC, and even more sensitive and specific than CT-scanning in the detection of mediastinal and distant metastases from NSCLC. The co-registration of CT and PET images enables even greater accuracy than either modality alone, while the functional imaging inherent in PET may better facilitate the distinction between benign and malignant structures. Overall, the superior tumor staging capability of PET (or PET-CT fusion) together with the improved dosimetry & diminished normal-tissue toxicity associated with deep inspiration breath-hold (DIBH) is expected to confer considerable clinical advantage to the use of gated PET in the radiotherapeutic planning and treatment of NSCLC.