Lung volume reproducibility under ABC control and self-sustained breath-holding

Abstract

An Active Breathing Coordinator (ABC) can be employed to induce breath-holds during CT imaging and radiotherapy of lung, breast and liver cancer, and recently during lung cancer MRI. The apparatus measures and controls respiratory volume, hence subject lung volume reproducibility is its principal measure of effectiveness. To assess ABC control quality, the intra-session reproducibility of ABC-induced lung volumes was evaluated and compared with that reached by applying the clinical standard of operator-guided self-sustained breath-holds on healthy volunteers during MRI. Inter-session reproducibility was investigated by repeating ABC-controlled breath-holds on a second visit. Additionally, lung volume agreement with ABC devices used with different imaging modalities in the same institution (MR, CT), or for a breast trial treatment, was assessed. Lung volumes were derived from three-dimensional (3D) T1-weighted MRI datasets by three observers employing semiautomatic lung delineation on a radiotherapy treatment planning system. Inter-observer variability was less than 6% of the delineated lung volumes. Lung volume agreement between the different conditions over all subjects was investigated using descriptive statistics. The ABC equipment dedicated for MR application exhibited good intra-session and inter-session lung volume reproducibility (1.8% and 3% lung volume variability on average, respectively). MR-assessed lung volumes were similar using different ABC equipment dedicated to MR, CT, or breast radiotherapy. Overall, lung volumes controlled by the same or different ABC devices agreed better than with self-controlled breath-holds, as suggested by the average ABC variation of 1.8% of the measured lung volumes (99 mL), compared to the 4.1% (226 mL) variability observed on average with self-sustained breath-holding.

Keywords: ABC; breath-hold; lung volume reproducibility.

Figure 1

(a) An example partition from a 3D T₁‐weighted image dataset (Volunteer 6, session 2), in the acquired axial and reconstructed coronal and sagittal orientation, during an MR‐ABC controlled breath‐hold. This image quality was typical for most acquisitions. The lung ROIs delineated by Observer 1, 2, and 3 appear in yellow, blue and red, respectively. (b) A similar example partition (Volunteer 4, session 2), presenting the worst image quality of this work due to a ghosting artifact. All images in (a) and (b) are equally windowed. The arrows point to instances of discrepancies between observers, which occurred mostly around the blood vessels and diaphragm. The original images were slightly cropped for display.

Figure 2

(a) A partition of the 3D image datasets of BH1 and BH4 of condition MR‐ABC 2 for Volunteer 5, with a small difference (4 mL) between their delineated lung volumes. Images are displayed in the acquired axial and reconstructed coronal and sagittal orientation. The image dataset of BH4 was rigidly registered on the BH1 dataset. The solid red and dotted yellow lines represent the delineated lung volume of BH1 and BH4, respectively. The images and lung contours demonstrate an excellent agreement. (b) A similarly positioned partition of self‐sustained BH4 rigidly registered on self‐sustained BH2 for the same volunteer, with a high difference (1370 mL) between the two delineated lung volumes, displayed in all three orientations. The images of the two breath‐holds present notable discrepancies in diaphragm, vessels and thorax position, displayed as blue and orange shaded regions.

Figure 3

Bland‐Altman plots assessing the agreement of the mean of four lung volumes delineated from T₁‐weighted 3D image datasets between ABC breath‐holding conditions over the six volunteers. (a) compares the two MR‐ABC sessions, (b) shows the volume comparison of the CT‐ABC to the trial‐ABC kit, while (c) and (d) compare the mean of the MR‐ABC sessions to the CT‐ABC and trial‐ABC, respectively. All plots have the same scale. The mean volume difference between two methods is numerically indicated in liters and as a blue solid line on every graph. The two dashed red lines denote the limits of agreement: mean volume difference ± 1.96 standard deviations (also mentioned on each graph in liters) of the differences for every comparison.