Distribution of Functional Liver Volume in Hepatocellular Carcinoma Patients with Portal Vein Tumor Thrombus in the 1st Branch and Main Trunk Using Single Photon Emission Computed Tomography—Application to Radiation Therapy

PURPOSE To analyze the distribution of functional liver volume (FLV) in the margin volume (MV) surrounding hepatocellular carcinoma (HCC) with portal vein tumor thrombus (PVTT) before radiation therapy (RT) and to verify the safety of single photon emission computed tomography-based three-dimensional conformal radiotherapy (SPECT-B3DCRT) by exploring the relation of FLV in MV to radiation-induced liver disease (RILD). METHODS AND MATERIALS Clinical target volume (CTV) included main tumor and PVTT, and planning target volume (PTV) included CTV with a 10 mm margin. MV was defined as PTV-CTV. FLV ratio in MV was calculated as FLV in MV/MV × 100 (%). The two high-dose beams were planned to irradiate FLV as little as possible. Fifty-seven cases of HCC (26/57, 46%; Child-Pugh grade B) with PVTT underwent SPECT-B3DCRT which targeted the CTV to a total dose of 45 Gy/18 fractions. The destructive ratio was defined as radiation induced dysfunctional volume/FLV × 100 (%). RESULTS We observed a significant negative correlation between FLV ratio in MV and CTV (p < 0.001). Three cases with CTVs of 287, 587 and 1184 cm3 experienced transient RILD. The FLV ratio in MV was highest in patients with RILD: nine patients with CTV of 200-300 cm3, three with CTV of 500-600 cm3, and two with CTV of 1100-1200 cm3. The destructive ratio yielded a mean value of 24.2 ± 1.5%. CONCLUSIONS Radiation planning that takes into account the distribution of FLV appears to result in the least possible RILD.