Radiobiologic Principles and the Role of Radiotherapy in Hematopoietic Cell Transplant and Chimeric Antigen Receptor T-Cell Therapy

Radiotherapy is an established therapeutic option for hematologic malignancies in a variety of contexts. In this chapter, we will review the mechanism of action of external beam radiotherapy and radiobiologic principles that guide dose and fractionation regimens commonly used today. We will discuss the role of radiotherapy before transplant, from myeloablative to reduced-intensity conditioning total-body-irradiation regimens, as well as total marrow and total lymphoid irradiation. We will also discuss the use of radiotherapy in unique clinical scenarios including extramedullary disease involving the central nervous system and skin. We will summarize the data supporting the use of radiotherapy in the setting of chimeric antigen receptor T-cell therapy, both in the bridging and salvage setting, and highlight considerations for radiotherapy dose, target, and timing.