“Rounding” the Size of Pulmonary Nodules

Rationale and Objectives

The objective of this study was to quantify the impact of different rounding methods on size measurements of pulmonary nodules and to determine the number of nodules that change management categories as a result of rounding.

Materials and Methods

For this retrospective institutional review board-approved study, we included 503 incidental pulmonary nodules (308 solid and 195 subsolid) from a data repository. Long and short axes were measured. Average diameters were calculated using four different rounding methods (method 1: no rounding; method 2: rounding only the average diameter to the closest millimeter; method 3: rounding only short and long axes; and method 4: rounding short and long axes and the average diameter to the closest millimeter). Nodules were classified for each rounding method according to the 2017 Fleischner Society guideline management categories. Measurements were compared among the four rounding methods using analysis of variance.

Results

Without rounding, the average nodule diameter was 15.67 ± 5.97 mm. This increased between 0.03 and 0.29 mm using rounding methods 2–4 (range: P < 0.001–0.017). The nodule size was more frequently rounded up (range: 52.1%–77.5%) than rounded down (range: 17.7%–42.5%) using rounding methods 2–4, as compared to no rounding. In the 308 solid nodules, up to 2.9% of the nodules changed management category, whereas none of the 195 subsolid nodules changed category.

Conclusions

Rounding methods have a small absolute but statically significant effect on nodule size, impacting management category in less than 3% of the nodules. This suggests that, in clinical practice, any rounding method can be used for determining nodule size without substantially biasing individual nodules toward given management categories.

Introduction

“Rounding” refers to the replacement of a number by another number of approximately the same value, but which is shorter and simpler to use . The newly published 2017 Fleischner Society guidelines for the management of pulmonary nodules recommend expressing nodule size “rounded” to the nearest millimeter . There are, however, different possible approaches to rounding the size of pulmonary nodules , but the guidelines are not explicit as to which of these approaches should be used.

Only one previous study has assessed the impact of rounding on size measurements in pulmonary nodules . Li et al.’s study was conducted in the context of computed tomography (CT) lung cancer screening and focused on the longitudinal evolution of nodule size . No previous study has investigated the influence of rounding on nodule size measurements in the context of managing incidentally detected pulmonary nodules, as described in the newly published 2017 Fleischner Society guidelines . Therefore, the purpose of our study was to quantify the impact of different rounding methods on size measurements of pulmonary nodules and to determine the number of nodules that change management categories as a result of rounding.

Materials and Methods

Study Material

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CT Acquisition

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Patient Population

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Nodule Measurements

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Statistical Analysis

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Results

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TABLE 1

Average Computed Tomography Diameter, Expressed in Millimeter, Among the Four Rounding Methods, Displayed as Means ± Standard Deviations, Together with 95% Confidence Intervals

Method 1 Method 2 Method 3 Method 4P Values All nodules

( n = 503) 15.67 ± 5.97 (15.15–16.19)

Range: 4.30–29.90 15.71 ± 5.97 (15.18–16.23)

Range: 4.00–30.00 15.71 ± 5.98 (15.19–16.24)

Range: 4.50–30.00 15.96 ± 6.01 (15.43–16.49)

Range: 5.00–30.00 M1 vs M2: 0.017

M1 vs M3: <0.001

M1 vs M4: <0.001

M2 vs M3: 0.568

M2 vs M4: <0.001

M3 vs M4: <0.001 Solid nodules

( n = 308) 14.73 ± 5.88 (15.13–16.17)

Range: 4.30–29.90 14.79 ± 5.88 (15.16–16.21)

Range: 4.00–30.00 14.77 ± 5.90 (15.17–16.22)

Range: 4.50–30.00 15.02 ± 5.92 (15.41–16.47)

Range: 5.00–30.00 M1 vs M2: 0.001

M1 vs M3: 0.001

M1 vs M4: <0.001

M2 vs M3: 0.338

M2 vs M4: <0.001

M3 vs M4: <0.001 Subsolid nodules

( n = 195) 17.16 ± 5.83 (16.34–17.98)

Range, 7.10–29.80 17.15 ± 5.83 (16.33–17.98)

Range: 7.00–30.00 17.21 ± 5.82 (16.39–18.03)

Range: 7.00–29.50 17.44 ± 5.87 (16.61–18.27)

Range: 7.00–30.00 M1 vs M2: 0.756

M1 vs M3: 0.004

M1 vs M4: <0.001

M2 vs M3: 0.054

M2 vs M4: <0.001

M3 vs M4: <0.001

TABLE 2

Distributions of Nodules ( n = 503) That Were Rounded Up, Rounded Down, or with No Change in Nodule Diameter Using Rounding Methods 2–4 with Respect to No Rounding (Method 1)

Nodule Diameter Method 2 Method 3 Method 4 Rounded up 262 (52.1) 271 (53.9) 390 (77.5) Rounded down 214 (42.5) 184 (36.6) 89 (17.7) No change 27 (5.4) 48 (9.5) 24 (4.8)

Numbers in parentheses represent percentages.

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TABLE 3

Distribution of Solid Nodules ( n = 308) for Each Rounding Method According to Management Categories in the 2017 Guidelines by the Fleischner Society

Categories Method 1 Method 2 Method 3 Method 4 <6 mm 6 (2.0) 3 (1.0) 4 (1.3) 3 (1.0) 6–8 mm 33 (10.7) 42 (13.6) 38 (12.3) 39 (12.7) >8 mm 269 (87.3) 263 (85.4) 266 (86.4) 266 (86.4)

Numbers in parentheses represent percentages.

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Discussion

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Acknowledgment

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“Rounding” the Size of Pulmonary Nodules

Rationale and Objectives

Materials and Methods

Results

Conclusions

Introduction

Materials and Methods

Study Material

CT Acquisition

Patient Population

Nodule Measurements

Statistical Analysis

Results

Discussion

Acknowledgment

References

Further Reading

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