The past, present and future of radiation treatment of cancers in the liver: a physicist’s perspective
Eugene Wong
Associate Professor
Dept. Physics & Astronomy, University of Western Ontario
Tuesday, September 11, 2012

Radiotherapy has evolved rapidly in the past twenty years. Previous toxic whole liver treatments with radiation doses that at best relieve cancer symptoms are now targeted to the tumours only, guided by imaging and triggering of radiation delivery based on patient’s respiration. We can now escalate dose to levels impossible before, only limited by surrounding normal tissues.  Along with earlier diagnoses and better follow up, liver metastases from colorectal diseases, for instance, are diagnosed earlier, with smaller tumors, and often solitary. This state of limited metastases is now known as oligometastasis, and long term cure is possible with aggressive treatments.  Risks of complications for these patients are estimated by a model of liver normal tissue complication probability (NTCP) based on the treatment plans and information from prior clinical trials. Since tumours are of different sizes and locations with respect to the liver, patients received different prescriptions.  We will show in this talk how we took advantage of the different dose prescriptions to extract tumour control probability (TCP) for liver metastases and compared it to that of primary liver cancers.  Such dose-response curve will be used as a population-based prediction of treatment outcome. To explore patient-specific dose prescription, we began investigating into liver tumour blood flow imaging, with the hypothesis that low blood flow imply hypoxia, conferring radiation resistance.  The theory and practice of such liver blood flow imaging will be reviewed. Last but not least, coming full circle, we have recently begun reviewing toxicities from treating this group of patients with an eye to validate or update the existing NTCP model parameters used in the clinic.