title: Plan robustness in field junction region from arcs with different patient orientation in total marrow irradiation with VMAT.
abstract: BACKGROUND
  The cranial-caudal (CC) maximum LINAC couch shift is usually around 130-150 cm; therefore total marrow (and lymph-nodes) irradiation (TMI-TMLI) requires two different plans, one with patient head-first-supine ("body plan" - skull-thighs) and a second feet-first-supine ("legs plan" - feet-femurs head). A challenging planning is required to manage the region in which the radiation come from the two plans (that cannot be automatically optimized together). We studied a robust way to produce a plan sum in this field junction region without creating under/over dosage on PTV and hotspots out.
  
  
  METHODS
  Twenty-one patients candidates to bone marrow transplantation were treated with TMI-TMLI on TrueBeam using RapidArc technique. All body bones were defined as PTV and, for TMLI, lymph-nodes and spleen were included, too. The two plans according to ALARA principle were optimized. In particular, in the overlapping region (PTVJ), two specular sigmoid dosimetric shapes were adopted for obtaining homogeneous integral dose. Furthermore, 144 plans from four patients were calculated to evaluate plan robustness.
  
  
  RESULTS
  In all patients, 95% of the prescription dose covered >99% of PTVJ. Regarding the robustness study, differences <1% were found for mean doses to PTVJ and surrounding healthy tissue (HT) for 5 mm shifts. Maximum dose increased up to 21.4% for 10 mm shifts in CC. PTVJ V95% decreased of around 9% (range -3.4% to 24.3%) revealing possible target under-dosage.
  
  
  CONCLUSIONS
  Dosimetric field junction from two different plans is possible for TMI-TMLI with optimal target coverage. The correct repositioning between the two plans is fundamental, in particular in CC direction.
authors.affiliation: Physics Service of Radiation Oncology Dept, Clinical and Research Center, Rozzano, Milan, Italy. Electronic address: pietro.mancosu@humanitas.it.
authors.forename: Pietro
authors.initials: P
authors.lastname: Mancosu
authors.affiliation: Radiation Oncology Dept, Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Piera
authors.initials: P
authors.lastname: Navarria
authors.affiliation: Bone Marrow Transplantation Unit, Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Castagna
authors.affiliation: Physics Service of Radiation Oncology Dept, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Reggiori
authors.affiliation: Physics Service of Radiation Oncology Dept, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Stravato
authors.affiliation: Physics Service of Radiation Oncology Dept, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Gaudino
authors.affiliation: Bone Marrow Transplantation Unit, Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Sarina
authors.affiliation: Physics Service of Radiation Oncology Dept, Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tomatis
authors.affiliation: Radiation Oncology Dept, Humanitas Clinical and Research Center, Rozzano, Milan, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Scorsetti
mesh_terms: D001853:Bone Marrow / Q000528:radiation effects*; D054893:Cone-Beam Computed Tomography; D006801:Humans; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D056888:Patient Positioning; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
keywords: Field junction; Radiotherapy; Total marrow irradiation; Volumetric modulated arc therapy (VMAT)