In single photon emission computed tomography-based three-dimensional radiotherapy (SPECT-B-3DCRT), images of Tc-99m galactosyl human serum albumin (GSA), which bind to receptors on functional liver cells, are merged with the computed tomography simulation images. Functional liver is defined as the area of normal liver where GSA accumulation exceeds that of hepatocellular carcinoma (HCC). In cirrhotic patients with a gigantic, proton-beam-untreatable HCC of ≥ 14 cm in diameter, the use of SPECT-B-3DCRT in combination with transcatheter arterial chemoembolization achieved a 2-year local tumor control rate of 78.6% and a 2-year survival rate of 33.3%. SPECT-B-3DCRT was applied to HCC to preserve as much functional liver as possible. Sixty-four patients with HCC, including 30 with Child B liver cirrhosis, received SPECT-B-3DCRT and none experienced fatal radiation-induced liver disease (RILD). The Child-Pugh score deteriorated by 1 or 2 in > 20% of functional liver volume that was irradiated with ≥ 20 Gy. The deterioration in the Child-Pugh score decreased when the radiation plan was designed to irradiate ≤ 20% of the functional liver volume in patients given doses of ≥ 20 Gy (FLV20Gy). Therefore, FLV20Gy ≤ 20% may represent a safety index to prevent RILD during 3DCRT for HCC. To supplement FLV20Gy as a qualitative index, we propose a quantitative indicator, F 20Gy, which was calculated as F 20Gy = 100% × (the GSA count in the area irradiated with ≥ 20 Gy)/(the GSA count in the whole liver).

AIM:To retrospectively explore the cutoff values that predict radiation-induced liver disease (RILD) in hepatocellular carcinoma (HCC) patients with portal vein tumor thrombus (PVTT) in the main trunk and/or the first branch who had previously received singlephoton-emission computed tomography (SPECT)-based threedimensional conformal radiotherapy (3DCRT; SPECT-B-3DCRT) using Tc-99m-galactosyl human serum albumin (Tc-99m GSA). METHODS: Seventy-five HCC patients with PVTT underwent SPECT-B-3DCRT (total dose of 45 Gy/18 fractions) in the stopbreathing position with an error of ≤5 mm. SPECT allowed the minimum possible irradiation of the functional liver (FL). ChildPugh score deterioration (CPSD) by 2 (=RILD) or CPSD by 1 was scored within four months of completing SPECT-B-3DCRT. Receiver-operating characteristic (ROC) analysis of the outcomes RILD vs CPSD by 1 was conducted to determine the accuracy and cutoff values for FLV20Gy (percentage of FL volume receiving ≥20 Gy), F20Gy (GSA counts within the irradiated liver area receiving ≥20 Gy ×100/GSA counts in the whole liver), F20Gy/LHL15 (liver radioactivity counts at 15 min/heart plus liver radioactivity counts at 15 min), and F20Gy/total count ratio (liver radioactivity counts/liver plus total background radioactivity counts). RESULTS:The cutoff values and accuracy of FLV20Gy, F20Gy, F20Gy/ LHL15, and F20Gy/total count ratio were 26.4 and 0.826 (p=0.024), 30.2 and 0.913 (p=0.004), 37.7 and 0.913 (p=0.001), and 43.0 and 0.957 (p<0.001), respectively. CONCLUSION: An F20Gy/total count ratio of 43.0 is the most reliable cutoff value for preventing RILD.

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