Positron Emission Tomography/CT after Yttrium-90 Radioembolization: Current and Future Applications

Assessment of radiation sensitivity of unresectable intrahepatic cholangiocarcinoma in a series of patients submitted to radioembolization with yttrium-90 resin microspheres

Radioembolization is a valuable therapeutic option in patients with unresectable intrahepatic cholangiocarcinoma. The essential implementation of the absorbed dose calculation methods should take into account also the specific tumor radiosensitivity, expressed by the α parameter. Purpose of this study was to retrospectively calculate it in a series of patients with unresectable intrahepatic cholangiocarcinoma submitted to radioembolization. Twenty-one therapeutic procedures in 15 patients were analysed. Tumor absorbed doses were calculated processing the post-therapeutic ⁹⁰Y-PET/CT images and the pre-treatment contrast-enhanced CT scans. Tumor absorbed dose and pre- and post-treatment tumor volumes were used to calculate α and α_3D parameters (dividing targeted liver in n voxels of the same volume with specific voxel absorbed dose). A tumor volume reduction was observed after treatment. The median of tumor average absorbed dose was 93 Gy (95% CI 81–119) and its correlation with the residual tumor mass was statistically significant. The median of α and α_3D parameters was 0.005 Gy⁻¹ (95% CI 0.004–0.008) and 0.007 Gy⁻¹ (95% CI 0.005–0.015), respectively. Multivariate analysis showed tumor volume and tumor absorbed dose as significant predictors of the time to tumor progression. The knowledge of radiobiological parameters gives the possibility to decide the administered activity in order to improve the outcome of the treatment.

The physics of radioembolization

Radioembolization is an established treatment for chemoresistant and unresectable liver cancers. Currently, treatment planning is often based on semi-empirical methods, which yield acceptable toxicity profiles and have enabled the large-scale application in a palliative setting. However, recently, five large randomized controlled trials using resin microspheres failed to demonstrate a significant improvement in either progression-free survival or overall survival in both hepatocellular carcinoma and metastatic colorectal cancer. One reason for this might be that the activity prescription methods used in these studies are suboptimal for many patients.In this review, the current dosimetric methods and their caveats are evaluated. Furthermore, the current state-of-the-art of image-guided dosimetry and advanced radiobiological modeling is reviewed from a physics' perspective. The current literature is explored for the observation of robust dose-response relationships followed by an overview of recent advancements in quantitative image reconstruction in relation to image-guided dosimetry.This review is concluded with a discussion on areas where further research is necessary in order to arrive at a personalized treatment method that provides optimal tumor control and is clinically feasible.

PET-based radiation therapy planning

In this review, we review the literature on the use of PET in radiation treatment planning, with an emphasis on describing our institutional methodology (where applicable). This discussion is intended to provide other radiation oncologists with methodological details on the use of PET imaging for treatment planning in radiation oncology, or other oncologists with an introduction to the use of PET in planning radiation therapy.

Cost effectiveness of radioembolization compared with conventional transarterial chemoembolization for treatment of hepatocellular carcinoma

PURPOSE

To assess cost effectiveness of radioembolization versus conventional transarterial chemoembolization.

MATERIALS AND METHODS

The cost of radioembolization versus conventional transarterial chemoembolization was determined based on Medicare reimbursements. Three patient subgroups were defined based on the Barcelona Clinic Liver Cancer (BCLC) classification system (A, B, or C). Efficacy and safety outcomes after each procedure were obtained from the literature. A Monte Carlo case-based simulation was designed for 60 months in 250 patients in each subgroup. Survival was calculated based on average survival from the literature and the Monte Carlo model. The primary outcome was the cost effectiveness of radioembolization over transarterial chemoembolization by considering calculated survival.

RESULTS

The costs approached $17,000 for transarterial chemoembolization versus $31,000 or $48,000 for unilobar or bilobar radioembolization, respectively. Based on the simulation, median estimated survival was greater with transarterial chemoembolization than radioembolization in BCLC-A and BCLC-B subgroups (40 months vs 30 months and 23 months vs 16 months, respectively, P = .001). However, in the BCLC-C subgroup, survival was greater with radioembolization than transarterial chemoembolization (13 months vs 17 months, P = .001). The incremental cost-effectiveness ratio of radioembolization over transarterial chemoembolization in the BCLC-C subgroup was $360 per month. The results were dependent on bilobar versus unilobar radioembolization and the total number of radioembolization procedures.

CONCLUSIONS

The model suggests radioembolization costs may be justified for patients with BCLC-C disease, whereas radioembolization may not be cost effective in patients with BCLC-A disease; however, many patients with BCLC-C disease have extensive disease precluding locoregional therapies. Secondary considerations may determine treatment choice in more borderline patients (BCLC-B disease) because there is no persistent survival benefit with radioembolization.