Distinguishing radiation fibrosis from tumour recurrence after stereotactic ablative radiotherapy (SABR) for lung cancer: A quantitative analysis of CT density changes

Figures & data

Table I. Baseline patient and treatment variables.

	Total (n = 22 patients, with 24 tumors) Median (range) or number (%)
Age (n = 22)	69 (49–84)
Gender (n = 22)
Male	14 (63.6%)
Female	8 (36.4%)
Charlson Score* (n = 22)	5 (1–10)
Planning target volume (n = 24)	20.4 cm^3 (4.5–144.4 cm^3)
Fractionation schedule (n = 24)
3 × 20 Gy	14 (58.3%)
5 × 11 Gy	1 (4.2%)
5 × 12 Gy	4 (16.7%)
8 × 7.5 Gy	5 (20.8%)
Treatment type (n = 24)
Fixed beam	21 (87.5%)
RapidArc	3 (12.5%)
Tumour location (n = 24)
Left upper lobe	4 (16.7%)
Left lower lobe	2 (8.3%)
Right upper lobe	10 (41.7%)
Right middle lobe	3 (12.5%)
Right lower lobe	5 (20.8%)

*age adjusted Charlson, current lung cancer not scored as comorbidity.

Figure 1. Manual contours throughout a course of follow-up for a patient whose cancer recurred. The solid lines represent consolidative changes, and the dashed lines represent ground glass opacity (GGO).

Figure 2. The standard deviation (SD) of CT density was used as a basic texture measure. Three examples from ground glass opacity of patients in this study, showing the differences in texture with the varying SDs: a) 50.1 HU, b) 85.8 HU, c) 123.4 HU.

Table II. Baseline pre-treatment imaging characteristics.

	Recurrence Mean ± 95% CI	Benign fibrosis Mean ± 95% CI
Pre-treatment CT density (p = 0.434)	−104.8 ± 34.40 HU	−124.6 ± 34.43 HU
Pre-treatment RECIST (p = 0.052)	3.55 ± 1.01 cm	2.36 ± 0.43 cm
Pre-treatment 3D volume (p = 0.096)	22.29 ± 16.27 cm^3	6.67 ± 4.66 cm^3

*Standard deviation of CT density is not presented in this table, as this was calculated on the GGO areas and only the consolidative regions were contoured on the pre-treatment scans.

Figure 3. Cumulative size measures of the consolidative regions throughout follow-up post-SABR; all values are the mean ± 95% CI. a) RECIST and b) 3D volume. *Indicates statistical significance at p ≤ 0.05.

Figure 4. Cumulative appearance measures of the ground glass opacity regions throughout follow-up post-SABR; a) Mean (± 95% CI) CT density, and b) standard deviation (± 95% CI) of CT density. *Indicates statistical significance at p ≤ 0.05.

Figure 5. Cumulative appearance measures of the consolidative regions throughout follow-up post-SABR; a) Mean (± 95% CI) CT density, and b) standard deviation (± 95% CI) of CT density. Indicates statistical significance at p ≤ 0.05.