Radiation protection in the imaging of hepatocellular carcinoma patients for diagnosis and follow-up management

Abstract

In Hong Kong, hepatocellular carcinoma (HCC) is the fourth most common malignancy and the third leading cause of cancer deaths. Advances in surgical techniques have improved the chance of curative treatment for HCC. Radiologic imaging modalities, including relatively high radiation dose modalities of Computed Tomography (CT) scan and increasingly, positron emission tomography/computed tomography (PET/CT) scan, are accepted imaging modalities for pre- and post-treatment management of HCC. The objective of the present study was to describe and evaluate the current status of imaging protocols for HCC from the radiological protection point of view, with the goals to improve justification in terms of risk/benefit evaluation of imaging surveillance by CT for patients post-hepatectomy and post-liver transplant, and to investigate the radiation dosimetry of a novel dual-tracer PET-CT scan for HCC detection. The first two studies aimed to determine if current surveillance strategies may be appropriate so that the frequency of scans may be reduced in HCC patients post curative liver resection and transplantation (LT). 260 (216 male, 44 female) and 125 (108 male, 17 female) consecutive HCC patients who underwent curative liver resection and LT were retrospectively reviewed with the institutional review board (IRB) approval, respectively. Through stratification of patients into different recurrence risk groups based on Classification and Regression Tree analysis, the impacts of alternative surveillance schedules for different risk groups were evaluated. For patients post-resection in low- and intermediate-risk groups, no significant difference in average recurrence detection rate was found by extending the schedule to every 4 months for the 1st two years from current 3 months (p=0.386 and 0.317, respectively), and by extending the schedule to every 12 months for the subsequent three years from current 6 months (p=0.331 and 0.125, respectively). For patients post-transplantation, for low- and high-risk group, recurrence-free survival times were not significantly different in the first five years after transplantation when the interval was extended from current 3 months to 6 months (p=0.878 and 0.823, respectively). The above would result in 35.7% and 50% reduction in the number of scans with concomitant radiation dose reduction and cost savings over the five year follow-up period for patients after resection and transplantation, respectively. For the 3rd study, combined dual-tracer (18F-FDG and 11C-Acetate) PET/CT, increasingly utilized for staging HCC was evaluated with the aim to characterize the radiation dose of combined whole-body dual-tracer PET/CT protocols. 14 consecutive whole-body dual-tracer PET/CT scans were retrospectively reviewed with IRB approval. OLINDA/EXM and VirtualDose codes were used to estimate patient specific internal dose exposure in each organ, and organ equivalent doses from each CT series, respectively. The total effective doses of the combined whole-body dual-tracer PET/CT studies for male and female patients were 28.84±10.18 and 23.19±4.61 mSv, respectively. Overall, the useful information obtained in this study would be helpful to guide the use of radiologic imaging modalities for pre- and post-treatment management of HCC in improving the process for justification of radiation exposure.