CT patterns and serial CT Changes in lung Cancer patients post stereotactic body radiotherapy (SBRT)

Abstract

Background: To evaluate computed tomography (CT) patterns of post-SBRT lung injury in lung cancer and identify time points of serial CT changes.

Materials and methods: One hundred eighty-three tumors in 170 patients were evaluated on sequential CTs within 29 months (median). Frequencies of post-SBRT CT patterns and time points of initiation and duration were assessed. Duration of increase of primary lesion or surrounding injury without evidence of local recurrence and time to stabilization or local recurrence were evaluated.

Results: Post-SBRT CT patterns could overlap in the same patient and were nodule-like pattern (69%), consolidation with ground glass opacity (GGO) (41%), modified conventional pattern (39%), peribronchial/patchy consolidation (42%), patchy GGO (24%), diffuse consolidation (16%), "orbit sign" (21%), mass-like pattern (19%), scar-like pattern (15%) and diffuse GGO (3%). Patchy GGO started at 4 months post-SBRT. Peribronchial/patchy consolidation and consolidation with GGO started at 4 and 5 months respectively. Diffuse consolidation, diffuse GGO and orbit sign started at 5, 6 and 8 months respectively. Mass-like, modified conventional and scar-like pattern started at 8, 12 and 12 months respectively. Primary lesion (n = 11) or surrounding injury (n = 85) increased up to 13 months. Primary lesion (n = 119) or surrounding injury (n = 115) started to decrease at 4 and 9 months respectively. Time to stabilization was 20 months. The most common CT pattern at stabilization was modified conventional pattern (49%), scar-like pattern (23%) and mass-like pattern (12%). Local recurrence (n = 15) occurred at a median time of 18 months.

Conclusion: Different CT patterns of lung injury post-SBRT appear in predictable time points and have variable but predictable duration. Familiarity with these patterns and timeframes of appearance helps differentiate them from local recurrence.

Keywords: CT patterns; Computed tomography; Lung cancer; Radiation induced lung injury; Stereotactic body radiotherapy.

Fig. 1

The flow chart describes the number of patients that underwent SBRT in our institution between 2008 and 2012 and the inclusion and exclusion criteria of the study

Fig. 2

SBRT-treated lung cancer demonstrates stabilization at 61 months: a) Isodose multiplanar images for SBRT planning. b) Pre-SBRT CT shows a solid nodule. c) 10 months (mo) post-SBRT the primary lesion slightly decreased in size with development of diffuse ground glass opacity surrounding the nodule. d) 24 mo post-SBRT “the orbit sign” pattern developed. 40 (e) and 49 mo (f) post-SBRT there was gradual increase in density “filling in” the area between the irradiated nodule and the surrounding curvilinear density gradually obscuring the “orbit sign”. g) 61 mo post-SBRT there was stabilization of “mass-like” pattern. h) 72 mo post-SBRT there was no interval change

Fig. 3

SBRT-treated lung cancer demonstrates local recurrence at 35 months: a) Isodose multiplanar images for planning. b) Pre-SBRT CT shows a cavitary mass in the left upper lobe. c) 6 mo post-SBRT, the lesion decreased in size. d) 16 mo post-SBRT, the primary lesion is obscured by surrounding consolidation and mild GGO. e) 20 mo post-SBRT there is architectural distortion in keeping with “modified conventional pattern”. f) 30 and g) 36 mo post-SBRT, the radiation changes became denser and more well-defined retaining the “modified conventional pattern”

Fig. 4

SBRT-treated lung cancer continues to decrease in size at 19 months: a) Isodose multiplanar images for planning. b) Pre-SBRT CT shows a part-solid nodule. c) 6 mo post-SBRT the size is stable, however the nodule is denser and there is surrounding focal peribronchial consolidation away from the nodule. d, e) 10 mo post-SBRT there is decrease in size of the primary lesion and development of homogeneously thick curvilinear density at a radius away from the center of the nodule in keeping with the “orbit-sign” (d). f) 19 mo post-SBRT there is further decrease in size of the primary lesion and mild shrinkage of the surrounding “orbit-sign”

Fig. 5

SBRT-treated lung cancer continues to decrease in size at 49 months: a) Isodose multiplanar images for planning. b) pre-SBRT CT shows a solid nodule. c) 6 mo post-SBRT, the primary lesion slightly decreases in size and there is mild adjacent peribronchial consolidation. d) 9 mo post-SBRT, the lesion significantly increases in overall size with mild surrounding peribronchial consolidation. e) 18 mo post-SBRT, the lesion size is unchanged and there is improvement of the surrounding peribronchial consolidation, f) 22 mo post-SBRT, there is mild decrease of the lesion size and resolution of surrounding peribronchial consolidation, g) 49 mo post-SBRT, there is further mild decrease in lesion size

Fig. 6

SBRT-treated lung cancer demonstrates stabilization at 35 months: a) Isodose multiplanar images for planning. b) Pre-SBRT CT shows a part-solid nodule. c) The nodule slightly decreased in size 9 months post-SBRT. d) 13 mo post-SBRT, the overall volume of the surrounding radiation changes obscuring the nodule increased in size with a pattern resembling “peribronchial consolidation”. e) 23 mo post-SBRT, the radiation changes decreased in size demonstrating a “scar-like” pattern and f) in 35 mo, there was stabilization of the “scar-like” pattern. g) 48 mo post-SBRT there was no change. Coronal (h) and sagittal (i) reconstruction at 48 mo (same time point as in fig. 5f) shows “scar-like pattern” after stabilization. The “width” of the lesion is small in 2 of the 3 planes (axial (g) and coronal (h)) compared to the third plane (sagittal (i)). To correctly identify the “scar-like pattern” careful evaluation of all 3 planes is needed as the lesion usually looks “bulkier” in one plane giving the false impression of a more “mass-like” pattern

Fig. 7

SBRT-treated lung cancer demonstrates local recurrence at 35 months: a) Isodose multiplanar images for planning. b) pre-SBRT CT shows a solid nodule. c) 8 mo post-SBRT, the nodule has not changed significantly in size, however there is new surrounding GGO. d) 13 mo post-SBRT the lesion is stable and there is surrounding patchy GGO and peribronchial consolidation. e) 17 mo post-SBRT, there is slight increase of the nodule size with stable patchy GGO and consolidation. f) 26 mo post-SBRT, there is further mild interval increase of the nodule size and slight improvement of the surrounding GGO and consolidation. g) 31 mo post-SBRT, there is further interval increase of the lesion size (now a mass) and increased density of the adjacent radiation changes. h) 35 mo post-SBRT there is further increase of the primary lesion partially obscured by the surrounding radiation changes which demonstrate increased density. Local recurrence was established at this point. i) 39 mo post-SBRT, there is further increase of the primary lesion which is now inseparable for surrounding radiation changes which demonstrate further increased density

Fig. 8

SBRT-treated lung cancer demonstrates local recurrence at 5 years: a) Isodose multiplanar images for planning. b) pre-SBRT, CT shows a solid nodule (black arrow). Axial (c) and coronal plane (d) chest CT 3 years post-SBRT show “modified conventional pattern” that has stabilized. 5 years post-SBRT axial (e) and coronal (f) images show increased soft tissue density bulging on one side of the lesion (posteriorly on axial plane and superiorly on coronal plane, black arrows) in keeping with local recurrence