The Effect of Lung Volume on Nodule Size on CT

Rationale and Objectives

We sought to determine how measures of nodule diameter and volume on computed tomography (CT) vary with changes in inspiratory level.

Materials and Methods

CT scans were performed with inspiration suspended at total lung capacity (TLC) and then at residual volume (RV) in 41 subjects, in whom 75 indeterminate lung nodules were detected. A fully automated contouring program was used to segment the lungs; followed by segmentation of all nodules and the corresponding lobe using semiautomated contouring in both TLC and RV scans. The percent changes in lung and lobar volumes between TLC and RV were correlated with percent changes in nodule diameters and volumes.

Results

Both nodule diameter and volume varied nonuniformly from TLC to RV—some nodules decreased in size, while others increased. There was a 16.8% mean change in absolute volume across all nodules. Stratified by size, the mean value of the absolute percent volume changes for nodules ≥5 mm and <5 mm were not significantly different ( P = .26). Stratified by maximum attenuation, the mean value of the absolute percent volume changes between the TLC and RV series for noncalcified (17.7%, SD = 13.1) and completely calcified nodules (8.6% SD = 5.7) were significantly different ( P < .05).

Conclusion

Significant differences in nodule size were measured between TLC and RV scans. This has important implications for standardizing acquisition protocols in any setting where size and, more important, size change are being used for purposes of lung cancer staging, nodule characterization, or treatment response assessment.

The lung is one of the predilection organs of metastases in the body, and also the site of the most frequently occurring cancer in the world ( ). On CT, primary lung cancers and extrapulmonary metastatic lesions commonly present as noncalcified pulmonary nodules.

The measurement of pulmonary nodules can be made using unidimensional, bidimensional, or volumetric techniques. Historically, size measurements derived from CT have been the mainstay in determining response assessment to cytotoxic therapies. Using bidimensional methods developed by the World Health Organization (WHO), measurements are achieved by multiplying a tumor’s maximum diameter in the transverse plane by its largest perpendicular diameter on the same image, yielding a cross product. Pretreatment and post-treatment cross products are used to determine treatment response ( ). Under these guidelines, tumor response to treatment is classified into one of four categories: complete response, partial response, stable disease, and disease progression ( ). Response Evaluation Criteria in Solid Tumors (RECIST) criteria offer a simplified extraction of imaging data for wide application in clinical trials, presuming that linear measures are an adequate substitute for 2D methods ( ). RECIST criteria represent a unidimensional method, which corresponds to the sums of nodules’ longest diameters in pretreatment and post-treatment image sequences ( ).

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Methods and materials

Nodule Database

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Imaging Protocol

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Lung, Lobar, and Nodule Segmentation and Measurement

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Statistical Analyses

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Results

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Table 1

Size Characteristics of the nodule dataset

Value (75 nodules) Maximum axial diameter (mm) at TLC Maximum axial diameter (mm) at RV Nodule volume (mm 3 ) at TLC Nodule volume (mm 3 ) at RV Mean 9.3 9.3 390 377 Median 7.6 7.6 165 156 SD 4.6 4.7 559 516 Minimum 3.2 3.4 30 25 Maximum 22.4 22.5 2638 2300

TLC = total lung capacity; RV = residual volume.

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Table 2

Mean value of the absolute percent changes of nodule volume when the nodules are stratified by maximum HU (<200, [200, 1000], ≥1000) and size of nodules (<5 mm and ≥5 mm)

TLC maximum diameter Nodule maximum HU at TLC Total Variable <200 HU 200–1000 HU ≥1000 HU <5 mm N 6 2 0 8 Mean 22.21 8.42 • 18.76 SD 13.45 7.68 • 13.36 Median 21.54 8.42 • 17.20 Interquartile range 10.41 10.86 • 14.34 ≥5 mm N 45 14 8 67 Mean 17.14 19.44 8.55 16.60 SD 13.09 22.65 5.65 15.12 Median 14.00 9.37 6.89 11.95 Interquartile range 13.93 12.87 9.01 13.36 Total N 51 16 8 75 Mean 17.74 18.06 8.55 16.83 SD 13.10 21.51 5.65 14.87 Median 15.84 9.37 6.89 13.06 Interquartile range 17.56 12.65 9.01 13.42

TLC = total lung capacity; HU = Hounsfield units; SD = standard deviation; Interquartile range = 75th percentile − 25th percentile.

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Discussion

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Conclusion

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Acknowledgments

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References

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The Effect of Lung Volume on Nodule Size on CT

Rationale and Objectives

Materials and Methods

Results

Conclusion

Methods and materials

Nodule Database

Imaging Protocol

Lung, Lobar, and Nodule Segmentation and Measurement

Statistical Analyses

Results

Discussion

Conclusion

Acknowledgments

References

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