The Unique Role of Fluorodeoxyglucose-PET in Radioembolization

Mode of progression after radioembolization in patients with colorectal cancer liver metastases

Background

Radioembolization is an established treatment modality in colorectal cancer patients with liver-dominant disease in a salvage setting. Selection of patients who will benefit most is of vital importance. The aim of this study was to assess response (and mode of progression) at 3 months after radioembolization and the impact of baseline characteristics.

Methods

Three months after radioembolization with either yttrium-90 resin/glass or holmium-166, anatomic response, according to RECIST 1.1, was evaluated in 90 patients. Correlations between baseline characteristics and efficacy were evaluated. For more detailed analysis of progressive disease as a dismal clinical entity, distinction was made between intra- and extrahepatic progression, and between progression of existing metastases and new metastases.

Results

Forty-two patients (47%) had extrahepatic disease (up to five ≥ 1 cm lung nodules, and ≤ 2 cm lymph nodes) at baseline. No patients showed complete response, 5 (5.5%) patients had partial response, 16 (17.8%) had stable disease, and 69 (76.7%) had progressive disease. Most progressive patients (67/69; 97%) had new metastases (intra-hepatic N = 11, extrahepatic N = 32; or both N = 24). Significantly fewer patients had progressive disease in the group of patients presenting without extrahepatic metastases at baseline (63% versus 93%; p = 0.0016). Median overall survival in patients with extrahepatic disease was 6.5 months, versus 10 months in patients without extrahepatic disease at baseline (hazard ratio 1.79, 95%CI 1.24–2.57).

Conclusions

Response at 3-month follow-up and survival were heavily influenced by new metastases. Patients with extrahepatic disease at baseline had a worse outcome compared to patients without.

Dose-Effect Relationships of 166Ho Radioembolization in Colorectal Cancer

Radioembolization is a treatment option for colorectal cancer (CRC) patients with inoperable, chemorefractory hepatic metastases. Personalized treatment requires established dose thresholds. Hence, the aim of this study was to explore the relationship between dose and effect (i.e., response and toxicity) in CRC patients treated with ¹⁶⁶Ho radioembolization. Methods: CRC patients treated in the HEPAR II and SIM studies were analyzed. Absorbed doses were estimated using the activity distribution on posttreatment ¹⁶⁶Ho SPECT/CT. Metabolic response was assessed using the change in total-lesion glycolysis on ¹⁸F-FDG PET/CT between baseline and 3-mo follow-up. Toxicity between treatment and 3 mo was evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5, and its relationship with parenchyma-absorbed dose was assessed using linear models. The relationship between tumor-absorbed dose and patient- and tumor-level response was analyzed using linear mixed models. Using a threshold of 100% sensitivity for response, the threshold for a minimal mean tumor-absorbed dose was determined and its impact on survival was assessed. Results: Forty patients were included. The median parenchyma-absorbed dose was 37 Gy (range, 12-55 Gy). New CTCAE grade 3 or higher clinical and laboratory toxicity was present in 8 and 7 patients, respectively. For any clinical toxicity (highest grade per patient), the mean difference in parenchymal dose (Gy) per step increase in CTCAE grade category was 5.75 (95% CI, 1.18-10.32). On a patient level, metabolic response was as follows: complete response, n = 1; partial response, n = 11; stable disease, n = 17; and progressive disease, n = 8. The mean tumor-absorbed dose was 84% higher in patients with complete or partial response than in patients with progressive disease (95% CI, 20%-180%). Survival for patients with a mean tumor-absorbed dose of more than 90 Gy was significantly better than for patients with a mean tumor-absorbed dose of less than 90 Gy (hazard ratio, 0.16; 95% CI, 0.06-0.511). Conclusion: A significant dose-response relationship in CRC patients treated with ¹⁶⁶Ho radioembolization was established, and a positive association between toxicity and parenchymal dose was found. For future patients, it is advocated to use a ¹⁶⁶Ho scout dose to select patients and yo personalize the administered activity, targeting a mean tumor-absorbed dose of more than 90 Gy and a parenchymal dose of less than 55 Gy.