Incorporating GSA-SPECT into CT-based dose-volume histograms for advanced hepatocellular carcinoma radiotherapy

Abstract

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 (_FLV_20Gy). Therefore, _FLV_20Gy≤ 20% may represent a safety index to prevent RILD during 3DCRT for HCC. To supplement _FLV_20Gy 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).

Keywords: Functional image-guided radiotherapy, Galactosyl human serum albumin, Dose-volume histogram, Three-dimensional radiotherapy, Hepatocellular carcinoma

Core tip: Three-dimensional conformal radiotherapy, which is designed to preserve functional liver, can be visualized by single photon emission computed tomography with Tc-99m-galactosyl human serum albumin (GSA). This treatment modality has promising therapeutic effects for hepatocellular carcinomas (HCCs) of > 14 cm in diameter that are unmanageable by proton beam therapy. A treatment plan designed to irradiate ≤ 20% of the functional liver volume (_FLV_20Gy≤ 20%) did not cause radiation-induced liver disease. Therefore, _FLV_20Gy≤ 20% may be a useful safety marker for three-dimensional radiotherapy of HCC of various sizes. It is also possible to estimate the effects of radiotherapy on the liver by dividing the GSA count in the region of the liver irradiated with ≥ 20 Gy by the GSA count of the entire liver.