Abstract

Background

Colorectal cancer (CRC) is a common cause of cancer-related deaths (12.2% overall mortality, GLOBOCAN 2012 v1.0). Approximately half of CRC patients develop metastasis (mCRC) to the liver. SIRT involves injection of yttrium-90 (⁹⁰Y) radiolabelled resin microspheres into the arterial blood supply of liver tumours. The purpose of this study was to conduct a lesion-by-lesion analysis to establish a dose-response relationship.

Method

A retrospective review of 24 SIRT patients (99 lesions) was conducted. SPECT images were transformed into dose maps using an in-house MATLAB script and the direct deposition dosimetry method. The ⁹⁰Y S‑value was generated by Monte Carlo-simulation using the EGSnrc/EGS++ code. Baseline and follow-up CT scans were segmented to derive liver and lesion volumes. Mean, median, and D70 (minimum dose to 70% of lesion volume) values derived from dose maps were correlated to change in lesion volume and RECIST 1.1 outcome using linear and logistic regression, respectively.

Results

The median administered radioactivity was 1513 MBq (range 847-2185) for lobar and bilobar administrations. The median uniform normal liver dose was 26.3 Gy (range 15.4-41.3, IQR 22.3-30.6) and median lesion dose was 32.8 Gy (range 2.3-90.0, IQR 23.4-48.2). Stable disease or partial response was observed in 17 (71%) patients. Radiation absorbed dose correlated with lesion response (i.e. a 1 Gy increase in mean, median, and D70 dose resulted in reduction in lesion volume by 2.7%, 2.7%, and 2.3%, respectively, p<0.02). Higher lesion doses were associated with a higher probability of RECIST response (odds ratio of 1.05, 1.05, and 1.04 for a 1 Gy increase in mean, median, and D70 doses, respectively, p<0.2).

Conclusion

Higher mean, median, and D70 doses are associated with a decrease in lesion volume and an increased probability of RECIST response. The type of analysis presented here will allow suboptimally-treated liver lesions to be managed by a multi-modality approach.