Evaluating the Impact of Liver Vasculature Model Complexity for Estimating Dose to Circulating Blood During Radiation Therapy

Abstract

Purpose: To assess the impact of liver model complexity on the estimated radiation dose to circulating blood during radiation therapy.

Methods and materials: Six patients with hepatocellular carcinoma (HCC) were selected covering a range of clinical treatment volume (CTV) sizes and locations. Photon and proton treatment plans were generated for each patient. Planning computed tomography, CTV contours, and dose distributions were deformably registered to the reference livers provided by the International Commission on Radiological Protection report. Three vasculature models were considered: (1) main vascular tree (MVT), (2) coarse vascular tree (CVT) of 1045 vessels, and (3) detailed vascular tree (DVT) of 2041 vessels. Blood dose-volume histograms (bDVH_MVT, bDVH_CVT, and bDVH_DVT) and the mean circulating blood dose (μ_b,MVT, μ_b,CVT, and μ_b,DVT) were estimated using Monte Carlo simulations for all 3 models. The effect of varying blood velocity (v_b) in HCC tumors on dose estimation was also evaluated through increasing the tumor v_b by 1.5, 2, and 4.2 times.

Results: For the 3 lesions located in the left lobe, the estimated μ_b,MVT was lower than μ_b,DVT by an average ± standard deviation of (6 ± 4)% and (17 ± 7)% for photon and proton treatments, respectively. Smaller differences were found for lesions in the right lobe, where μ_b,MVT was on average (2 ± 1)% lower than μ_b,DVT for photon and (3 ± 1)% lower for proton treatments. More pronounced difference between μ_b,MVT and μ_b,DVT was seen in lesions with smaller CTV sizes. We also found that considering the elevated tumor v_b led to a reduction of estimated dose to circulating blood, with a maximum reduction in the estimated μ_b of 39% and 8% for CTV of 603 and 249 mL, respectively.

Conclusion: Our study revealed that the impact of liver vasculature model complexity on the estimated dose to blood depended on lesion-specific characteristics. For lesions with larger CTV size on the right liver lobe treated with photons, modeling only major vessels could generate bDVHs that are dosimetrically comparable with bDVHs of more complex vascular models. Increased tumor v_b resulted in a reduction of the estimated blood dose.