There was some great science at SIR this year. I found the abstract session on radioembolization particularly thought-provoking. A series of fascinating presentations from Marnix Lam (catch his lecture at WCIO this New York this month!) examined dose distribution following resin-based radioembolization in metastatic disease. It was one of those “duh-oh” moments when he illustrated how body surface area based dose calculations result in undertreating little people with big livers and overdosing big people with little livers. There was a 5-fold range in liver dose from highest to lowest, with increased toxicity in the high-dose patients and lack of tumor response in the low-dose patients.
The penetrating question from the audience (guess who?) was -- so what is the ideal liver-volume based dose of resin microspheres for metastatic disease? Clearly the 120Gy target for glass microspheres is unattainable with resin microspheres. The median liver dose in Lam’s analysis was 50Gy, above which both response and toxicity were observed, but he was unable to prognosticate a recommended dose based on the limited retrospective analysis performed.
The mystery continued with presentation of Northwestern’s dose escalation study of glass Y90 microspheres with capecitabine for metastatic colon cancer, in which liver does of 170 Gy have been reached without increase in toxicity. So how can >50 Gy of resin Y90 be toxic, and 170 Gy of glass Y90 be safe?
Yttrium radioembolization sure is a mystery.