Held-breath self-gating technique for radiotherapy of non-small-cell lung cancer: a feasibility study.
To examine the feasibility of a held-breath self-gating (HBSG) technique in the radiotherapy of lung cancer. Sixteen consecutive eligible and consenting patients undergoing radiotherapy for non-small-cell lung cancer were accrued for this study. The patients underwent a standardized training session and were then asked to breath hold at four points in the breathing cycle (maximal and end tidal, inspiration and expiration) while under fluoroscopic visualization. Plain films and video imaging with digital image analysis were used to record and measure the movement of the diaphragm, a tumor surrogate, in the superior-inferior axis. These measurements were obtained during and between multiple separate breath holds within one session and between breath holds in sessions held at least one day apart. Maximal inspiration and expiration tend to provide the best positional reliability, and the standard deviation of diaphragmatic position ranged from 0.13 to 2.57 mm, with an average of 0.97 mm. During a single breath hold, the diaphragmatic movement averaged 2.62 mm with a standard deviation of 1.28 mm. The day-to-day variation of diaphragmatic positions was less than 5 mm. The held-breath self-gating technique resulted in a reduction of diaphragmatic movement by an average of 11.9 mm when compared to that seen during tidal breathing. In the radiotherapeutic management of non-small-cell lung cancer, this HBSG technique offers a simple method that provides superior immobilization of the diaphragm compared to tidal breathing. Clinical implementation of this technique should allow for a reduction of treatment margins, thus sparing more normal tissues and facilitating dose escalation.