SU‐FF‐J‐77: Interfractional Reproducibility of Lung Tumor Position Using Breath Hold

Abstract

Purpose: The purpose of the present work is to quantify the reproducibility of the position of a lung tumor under breath‐hold conditions. Methods and Materials: Weekly computed tomography (CT) data sets under voluntary breath hold at normal end inspiration and end expiration were acquired for 18 patients with diagnosed non‐small cell lung cancer. Gross tumor volumes (GTV) were outlined by a radiation oncologist. The distances between the centers of the GTV and a bony reference landmark were evaluated on a weekly basis, and the standard deviations (SD) of the distances were taken as a metric for assessing tumor position reproducibility. Results: The mean SDs for end inspiration were as follows: lat − 0.27±0.12 cm; AP 0.34±0.21 cm; SI 0.42±0.22 cm; distance 0.32±0.18 cm, whereas for end expiration the mean SDs were as follows: lat 0.23±0.10 cm; AP 0.31±−.19 cm; SI 0.38±0.15 cm; distance 0.25±0.11 cm. Conclusions: Voluntary breath hold appears to be a reliable method of ensuring reproducibility of lung tumor position. Setup margins used in our present practice of 0.5 cm for kV image‐guided patient setups and 0.3 cm for cone‐beam CT‐guided patient setups appear to be appropriate. Reproducibility under end expiration appears to be slightly better than that under end inspiration but the difference may not be significant.Research sponsored in part by Philips Medical Systems.