Radiodosimetric estimates for radioembolic therapy of liver tumors: challenges and opportunities

Stereotactic body radiation therapy is associated with improved overall survival compared to chemoradiation or radioembolization in the treatment of unresectable intrahepatic cholangiocarcinoma

Background

Intrahepatic cholangiocarcinoma (ICC) is a highly lethal malignancy. For patients with locally advanced, unresectable disease, numerous liver-directed therapy options exist, including chemoradiation (CRT), stereotactic body radiation therapy (SBRT), and transarterial radioembolization (TARE). There is no randomized data to inform clinicians regarding the optimal treatment modality.

Method

We used the National Cancer Database (NCDB) to study the overall survival (OS) of patients with ICC treated with CRT, SBRT, and TARE. We used Cox proportional hazards modeling and inverse probability of treatment weighting (IPTW) to account for confounding variables.

Results

We identified 170 patients with unresected ICC treated with SBRT (n = 37), CRT (n = 61), or TARE (n = 72). SBRT was associated with higher OS compared to CRT (hazard ratio [HR] = 0.37; 95% confidence interval [CI] 0.20-0.68; p = 0.001) and TARE (HR = 0.40; 95% CI 0.22-0.74; p = 0.003). On multivariable analysis, SBRT remained associated with higher OS compared to CRT (HR = 0.44; 95% CI 0.21-0.91; p = 0.028) and TARE (HR = 0.42; 95% CI 0.21-0.84; p = 0.014). After IPTW (Bonferroni-adjusted significance threshold, α = 0.017), SBRT again had a statistically significant association with higher OS compared to CRT (HR = 0.22; 95% CI 0.11-0.44; p < 0.0001) and was nominally associated TARE (HR = 0.58; 95% CI 0.37-0.91; p = 0.019).

Conclusions

We found SBRT is associated with higher OS when compared to CRT or TARE for the treatment of unresectable ICC. Due to the retrospective nature of the study and potential selection bias, these findings should be evaluated prospectively.

Assessment of Treatment Response Following Yttrium-90 Transarterial Radioembolization of Liver Malignancies

Transarterial radioembolization using yttrium-90 microspheres is an established and effective treatment for liver malignancies. Determining response to this treatment is difficult due to the radical changes that occur in tissue as a response to radiation. Though accurate assessment of treatment response is paramount for proper patient disposition, there is currently no standardized assessment protocol. Current methods of assessment often consider changes in size, necrosis, vascularity, fluorodeoxyglucose-positron emission tomography FDG-PET metabolic activity, and diffusion using diffusion-weighted magnetic resonance imaging (DWI). Current methods of assessment require a lag time of one to two months post-treatment to determine treatment effectiveness. This delay is a hindrance to obtaining better patient outcomes, giving rise to a need to identify markers for faster determination of treatment efficacy.

A small-scale anatomical dosimetry model of the liver

Radionuclide therapy is a growing and promising approach for treating and prolonging the lives of patients with cancer. For therapies where high activities are administered, the liver can become a dose-limiting organ; often with a complex, non-uniform activity distribution and resulting non-uniform absorbed-dose distribution. This paper therefore presents a small-scale dosimetry model for various source-target combinations within the human liver microarchitecture. Using Monte Carlo simulations, Medical Internal Radiation Dose formalism-compatible specific absorbed fractions were calculated for monoenergetic electrons; photons; alpha particles; and (125)I, (90)Y, (211)At, (99m)Tc, (111)In, (177)Lu, (131)I and (18)F. S values and the ratio of local absorbed dose to the whole-organ average absorbed dose was calculated, enabling a transformation of dosimetry calculations from macro- to microstructure level. For heterogeneous activity distributions, for example uptake in Kupffer cells of radionuclides emitting low-energy electrons ((125)I) or high-LET alpha particles ((211)At) the target absorbed dose for the part of the space of Disse, closest to the source, was more than eight- and five-fold the average absorbed dose to the liver, respectively. With the increasing interest in radionuclide therapy of the liver, the presented model is an applicable tool for small-scale liver dosimetry in order to study detailed dose-effect relationships in the liver.