Risk-adapted strategy partial liver irradiation for the treatment of large volume metastatic liver disease

The liver is a common site of metastases from many solid organ malignancies. In patients with oligometastatic liver disease, systemic therapy, generally in combination with surgical resection, is considered standard of care. In colorectal cancer, this combined approach has improved fi ve-year survival rates to 50 – 60% [1]. However, only 10 – 25% of patients will be initially appropriate for surgery, due to unfavourable disease distribution or co-morbidities [2]. For the remainder, a number of non-surgical invasive and non-invasive ablative techniques may be used as alternative modalities to achieve local control. Of these, partial liver irradiation (PLI), (also known as stereotactic body radiation therapy, SBRT) represents an attractive non-invasive option, with a rapidly expanding body of evidence supporting its use. High rates of LC (60 – 90% at two years), together with an acceptable toxicity profi le ( 10% G3 toxicity) have led to it being increasingly integrated into the therapeutic pathway [3,4]. Here it competes with alternative local options such as radiofrequency ablation (RFA), cryotherapy, microwave, selective internal radiation therapy (SIRT) and trans-arterial chemoembolisation (TACE). Small, favourably located lesions may be successfully ablated by a number of these techniques with similar local control outcomes, as demonstrated in a recent matched pair analysis of RFA compared to SBRT [5]. More challenging is the management of large volume lesions, often situated adjacent to critical structures, where many of these techniques are unsuitable or are known to result in inferior LC results. In this sub-group signifi cantly less reported experience exists, both in the use of PLI and alternative strategies. We have approached the safe treatment of large lesions with SBRT by individualising the radiation dose, using a normal tissue complication probability (NTCP) model. This effectively allows individualisation of tumour dose according to the modelled risk of radiation-induced liver disease (RILD) for each patient, a toxicity of particular concern when treating large lesions. The prescribed dose is dependent on the volume of normal liver tissue exposed to radiation and has been previously described [6]. This report evaluates the safety and effi cacy of a biologically driven prescription method for moderately hypofractionated RT strategy, in a heavily pretreated group of patients with, in general, larger volume liver metastases.