Using Functional Magnetic Resonance Imaging for Liver Sparing Stereotactic Ablative Body Radiotherapy

Background and Purpose<br/>Hepatocellular carcinoma (HCC) often develops 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 HCC, but the use of LMD does not take this into account. One possible way to improve HCC treatments is to use functional imaging to prioritise the sparing of healthy liver tissue.<br/><br/>Materials and Methods<br/>Anatomical T2 and functional Hepatica iron-corrected T1 images were provided for 10 patients by Perspectum. Functional liver volumes were segmented on the functional images using a threshold. HCC 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.<br/><br/>Results<br/>Sparing volumes varied greatly between patients, covering between 16 and 85% of the liver within the functional image. 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 D99% (p=0.04) but the sparing plans remained within the optimal tolerance and the D95% was not significantly different (p=0.2).<br/><br/>Conclusions<br/>This study has, for the first time, demonstrated the use of Hepatic sequences in radiotherapy showing significant reductions in dose to the healthy liver. Further work is needed to validate this work in HCC SABR patients.<br/>