Dosimetric analysis and comparison of three-dimensional conformal radiotherapy and intensity-modulated radiation therapy for patients with hepatocellular carcinoma and radiation-induced liver disease

Purpose: This study compares the difference in dose-volume data between three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for patients with hepatocellular carcinoma (HCC) and previously documented radiation-induced liver disease (RILD) after 3D-CRT. Methods and Materials: Between November 1993 and December 1999, 68 patients with HCC were treated with 3D-CRT at our institution. Twelve of them were diagnosed with RILD within 4 months of completion of 3D-CRT. RILD was defined as either anicteric elevation of alkaline phosphatase level of at least twofold and nonmalignant ascites, or elevated transaminases of at least fivefold the upper limit of normal or of pretreatment levels. Three-dimensional treatment planning using dose-volume histograms of normal liver was used to obtain the dose-volume data. These 12 patients with RILD were replanned with an IMRT planning system using the five-field (gantry angles 0°, 72°, 144°, 216°, and 288°) step-and-shoot technique to compare the dosimetric difference in targets and organs at risk between 3D-CRT and IMRT. Mean dose and normal tissue complication probability with literature-cited volume effect parameter of 0.32, curve steepness parameter of 0.15, and TD₅₀(1) of 40 Gy, were used for the liver, whereas volume fraction at a given dose level was used for other critical structures. Paired Student t-test with 2-tailed p < 0.05 was used to assess the statistical difference between the two techniques. Results: With comparable target coverage between 3D-CRT and five-field step-and-shoot IMRT, IMRT was able to obtain a large dose reduction in the spinal cord (5.7% vs. 33.2%, p = 0.007), and achieved at least similar organ sparing for kidneys and stomach. IMRT had diverse dosimetric effect on liver, with significant reduction in normal tissue complication probability (23.7% vs. 36.6%, p = 0.009), but significant increase in mean dose (2924 cGy vs. 2504 cGy, p = 0.009), as compared with 3D-CRT. Conclusion: IMRT is capable of preserving acceptable target coverage and improving or at least maintaining the nonhepatic organ sparing for patients with HCC and previously diagnosed RILD after 3D-CRT. The true impact of this technique on the liver remains unsettled and may depend on the exact volume effect of this organ.