chapter  15
Future directions in radioembolization
ByAlexander S. Pasciak, J. Mark McKinney, Yong C. Bradley
Pages 16

From the perspective of medical physicists, nuclear medicine radiologists, and radiation oncologists involved in radioembolization, the ideal direction of the future of this therapy may appear dierent than it does to interventional radiologists. is is primarily due to the dierences in the common procedures in which each of these groups normally participate. Interventional radiologists focus on procedures that, while technically demanding, normally do not involve the physics, mathematics, or the related precision commonly employed in radiation oncology and nuclear medicine. Further, while the technical considerations involved in a complex vascular intervention necessitate careful review of pretreatment structural and angiographic imaging, most nuclear medicine procedures are completely imaging based, focusing on both function and structure to diagnose and treat the patient. e distinction between these two groups and the ownership that interventional radiologists

normally have over patients undergoing radioembolization therapy have largely driven the radioembolization technical process in the past. Evidence for this can be seen in Chapters 4 and 5, where the manufacturer-recommended treatment-planning methods for radioembolization are largely based on simple empiric calculations that are only patient specic at the simplest level. For example, recall the specics of the body surface area (BSA) model oen employed for treatment planning using resin microspheres. In this model, the impact of height and weight on the prescribed dosage exceed the impact of relative tumor burden. Additionally, the tumor type, vascularity, prior treatment, homogeneity of uptake, and any other patient-specic factors are not considered. While BSA is widely used in medicine for determining dosages for medications such as chemotherapy, it certainly makes more sense for a systemic administration than for a local brachytherapy such as radioembolization. It is for these reasons that many medical physicists, nuclear medicine radiologists, and radiation oncologists new to radioembolization

15.1 Introduction 307 15.2 Background 308 15.3 Toward improved treatment planning 309 15.4 Improving efficacy and safety 311

15.4.1 Enhancement of T:N 311 15.4.2 Alternative methods to enhance tumor targeting 314

15.5 Toward improved posttreatment imaging 315 15.5.1 New tracers and methods 315 15.5.2 Image analysis 316

15.6 Toward extrahepatic tumor radioembolization 318

15.7 Conclusions 318 References 319

nd themselves immediately frustrated with the seeming lack of precision associated with the current standard of care in radioembolization treatment planning. It should be noted that this brief discussion of the commonly employed BSA treatment planning method for resin microspheres is not unique in its lack of tumor specicity-the recommended method for glass microspheres is even less tumor specic and does not account for tumor burden at all. ose looking for a more detailed review of these methods should refer to Chapter 5.