Determining the gross tumor volume for hepatocellular carcinoma radiotherapy based on multi-phase contrast-enhanced...

The aim of this study was to quantitatively analyze of the differences in determining the gross tumor volume (GTV) for hepatocellular carcinoma (HCC) radiotherapy using multi-phase contrast-enhanced magnetic resonance imaging (CE-MRI) and provide a reference for determining the GTV for radiotherapy of HCC.

This retrospective study analyzed 99 HCC patients (145 lesions) who underwent MR simulation. T₁-weighted imaging (T₁WI), contrast-enhanced T₁WI (CE-T₁WI) at 15 s, 45 s, 75 s, 150 s, and 20 min after contrast agent injection were performed, comprising a total of six imaging sequences. The GTVs identified on different sequences were grouped and fused in various combinations. The internal GTV (IGTV), which was the reference structure, was obtained by the fusion of all six sequences. Mean signal intensity (SI), volume, shape, and fibrous capsule (FC) thickness among GTVs were compared.

(1) The mean SI value of GTV_-T1WI, GTV_-15s-GTV_-20min in patients with transarterial chemoembolization (TACE) was lower by 14.09 % (GTV_-T1WI) to 31.31 % (GTV_-15s) compared with that in patients without TACE. Except for GTV_-T1WI, the differences in SI values between the two groups for other GTVs were statistically significant (p < 0.05). (2) The volumes of GTV_-T1WI, GTV_-15s-GTV_-20min ranged from 32.66-34.99 cm³. The volume differences between GTV_-45s and the other GTVs were statistically significant (p < 0.05), excluding the GTV_-T1WI. (3) Compared with the IGTV, the change trend of GTV volume reduction rate is consistent with that of dice similarity coefficients (DSC). (4) In the CE-T₁WI sequences (except for CE-T₁WI_-15s), FC measurement was possible in 39.31 % of lesions (57/145), with the largest mean thickness observed at 75 s.

Although single-phase CE-MRI introduces uncertainty in HCC GTV determination, combining different phases CE-MRI can enhance accuracy. The CE-T₁WI_-45s should be routinely included as a necessary scanning sequence.