Long-Term Characterization of MRI-Morphologic Alterations After Active Motion-Compensated Liver SBRT.

PURPOSE/OBJECTIVE(S) To characterize the post-SBRT MRI-morphologic alterations in long-term survivors with MRI-based follow-up (FU) in patients treated by actively motion managed gantry-based and robotic liver SBRT. MATERIALS/METHODS Patients treated with gantry-based (with breath-hold-gating and ultrasound tracking) or robotic-based SBRT (with real-time fiducial tracking) who had long-term follow-up (FU, ≥ 90 days) were evaluated. Post-SBRT MRI-evidenced morphologic alterations (MMAs) were contoured manually on each T1-weighted contrast-enhanced. Volumetric data and liver volume were documented at each FU. Change's dynamics and significance was assessed for each time point. RESULTS The median follow-up was 12.5 months [0.5 - 84]. Seventy PTVs from 62 patients were assessable. After 3 - 6 months, 95.7% (n = 67) of treated lesions developed MMAs with a median volume of 122.44 cc [8.17 - 699.34]. Characterization included 48 (71.6%) hypointense and 19 (28.4%) hyperintense MMAs. Twenty-one (31.3%) MMAs completely resolved after median 12 months [6 - 36] post-SBRT. At the last follow-up, 68.7% were still present (6 - 84 months). Thirty-seven (55.2%) MMAs did not resolve completely and reduced in volume with longer FU. Since the 3-month control baseline, a significant volume reduction to a median of 43.3% after 6 months (P < 0.001), 31% after 9 months (P = 0.022) and 13% after 12 - 24 months (P = 0.041), was observed. Liver volumes reduced to a mean 95.1% from the baseline at 3 months (P = 0.001) and remained afterwards unmodified. CONCLUSION Post-radiogenic MRI-morphologic alterations in peritumoral healthy liver tissue either completely resolve or significantly reduce in volume along the first 2 years after treatment. Clinical correlation should be further investigated.