Purpose: To describe volumetric changes of "radiation lobectomy," a manifestation of hepatic parenchymal response to lobar 90Y microsphere radioembolization. Methods: Twenty patients exhibiting this phenomenon were identified. Pre- and posttreatment absolute right and left hepatic lobar volume (HLV), relative HLV (rHLV = HLV/total liver volume), and degree of lobar atrophy (DA) or hypertrophy (DH) (DA or DH = |posttreatment rHLV - pretreatment rHLV|) were determined. Laboratory toxicities, tumor response, and patient survival were also assessed. Results: Twenty patients with primary (HCC, n = 17; peripheral cholangiocarcinoma, n = 3) liver malignancies demonstrated findings of radiation lobectomy. Initial absolute right and left HLV was 955 cm3 (range 644-1,842 cm3, rHLV = 57%) and 719 cm3 (range 328-1,387 cm3, rHLV = 43%), respectively. Following 90Y, absolute right HLV decreased to 460 cm3 (range 185-948 cm3 52% reduction, rHLV = 31%, DA = 26%, P < 0.0001), while absolute left HLV increased to 1,004 cm3 (range 560-1,558 cm3, 40% increase, rHLV = 69%, DH = 26%, P < 0.0001). No grade 3 or 4 bilirubin toxicities were encountered. Tumor response ranged from 55% to 70% by size criteria. Forty-six percent 5-year survival was achieved in HCC patients. Conclusions: Radiation lobectomy following 90Y radioembolization of right lobe tumors manifests extensive contralateral lobar hypertrophy, high response rates, and prolonged survival. This phenomenon was noted in 6.4% (20/315) of the entire cohort and 19.8% (20/101) of patients with unilobar right lobe tumors. Further investigation is necessary to determine contributing factors that may predict this effect.
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