Indications of IMRT, PRT and CIRT for HCC from comparisons of dosimetry and normal tissue complication possibility

Purpose To identify the indications for hepatocellular carcinoma (HCC) irradiated by intensity-modulated photon radiotherapy (IMRT), proton radiotherapy (PRT) or carbon-ion radiotherapy (CIRT) by comparing of dosimetric parameters and incidences of classic radiation-induced liver disease (RILD). Methods In all, 40 HCCs were divided into group A (tumors located > 1 cm away from gastrointestinal [GI] tract), and group B (tumors located < 1 cm away from GI tract). The prescribed curative doses were 60 Gy (relative biological effectiveness [RBE]) in 10 fractions for group A, and 67.5 Gy (RBE) in 15 fractions for group B. IMRT, PRT and CIRT plans were separately generated to reach the curative doses and coverage. Dosimetric parameters evaluated were mean dose to normal liver (MDTNL) and the volume of normal liver receiving more than 1 Gy (RBE) (V1). Lyman–Kutcher–Burman model was used to determine the incidences of classic RILD, and Power model of non-linear regression, to estimate the tumor volume that could be irradiated with the curative doses within dose constraint of MDTNL. Results With comparable target doses, the MDTNL (Gy [RBE]) were 18.8 ± 3.7, 13.5 ± 3.1 and 12.8 ± 2.7 in group A and 24.9 ± 7.1, 18.2 ± 3.7 and 17.5 ± 3.7 in group B, respectively, for IMRT, PRT and CIRT. The classic RILD incidences (%) were 22.3 ± 30.0 in IMRT, 2.3 ± 4.9 in PRT and 1.2 ± 2.4 in CIRT. V1 (%) were 89.9 ± 8.8, 43.0 ± 10.2 and 45.9 ± 8.8, respectively, for IMRT, PRT and CIRT. Conclusions PRT and CIRT could spare the liver more than IMRT. IMRT could deliver the curative doses to HCC up to a diameter of 7.9 cm; PRT, up to 13.2 cm; and CIRT, up to 14.8 cm.