Rationale, implementation considerations, delineation and planning target objective recommendations for volumetric modulated arc therapy and helical tomotherapy total body irradiation, total marrow irradiation, total marrow and lymphoid irradiation and total lymphoid irradiation.

As a component of myeloablative conditioning before allogeneic hematopoietic stem cell transplantation (HSCT), Total Body Irradiation (TBI) is employed in radiotherapy centers all over the world. In recent and coming years, many centers are changing their TBI setup to a conformal isocentric technique, providing superior homogeneity and control of the target prescription dose, and more freedom for individualized organ-at-risk sparing or dose-escalation. Also, more specifically bone-marrow- and/or lymphatics-targeted therapies such as Total Marrow (+ Lymphoid) Irradiation (TMI / TMLI), and Total Lymphoid Irradiation (TLI) are established and prospectively evaluated in several centers. With each center developing their own methods, a new practice heterogeneity is arising, as was the case for decades with conventional TBI. To provide a ground base - and therefore more options for more homogeneous and comparable practice - for centers who are implementing conformal isocentric techniques, a group of early adopters of isocentric conformal TBI and TM(L)I came together to convey issues they encountered during clinical implementation, and form consensus recommendations for delineation and planning targets, based on available literature evaluation and shared experience. These recommendations follow previously published recommendations regarding technical setup of conformal isocentric TBI / TM(L)I techniques.