Feasibility of using contrast-free quantitative magnetic resonance imaging for liver sparing stereotactic ablative body radiotherapy

Background and purpose

Tumours in the liver often develop on a background of liver cirrhosis and impaired liver function. As a result, radiotherapy treatments are limited by radiation-induced liver disease, parameterised by the liver mean dose (LMD). Liver function is highly heterogeneous, especially in liver cancer, but the use of LMD does not take this into account. One possible way to improve liver treatments is to use quantitative imaging techniques to assess liver health and prioritise the sparing of healthy liver tissue.

Materials and methods

Anatomical T2 and quantitative iron-corrected T1 (cT1) images were made available for 10 patients with liver metastases. Functional liver volumes were automatically segmented on the quantitative images using a threshold. Liver stereotactic ablative body radiotherapy (SABR) plans were made using a departmental protocol. Liver-sparing plans were then made by reducing the dose to the functional sub-volume.

Results

The sparing plans achieved a statistically significant ($p=0.002$) reduction in the functional liver mean dose, with a mean reduction of 1.4 Gy. The LMD was also significantly different ($p=0.002$) but had a smaller magnitude with a mean reduction of 0.7 Gy. There were some differences in the planning target volume D_99% ($p=0.04$) but the sparing plans remained within the optimal tolerance and the D_95% was not significantly different ($p=0.2$).

Conclusions

This study has, for the first time, demonstrated the use of cT1 maps in radiotherapy showing significant reductions in dose to the healthy liver. Further work is needed to validate this in liver cancer patients, who would likely benefit most.