title: Simultaneous tumour dose escalation and liver sparing in Stereotactic Body Radiation Therapy (SBRT) for liver tumours due to CTV-to-PTV margin reduction.
abstract: OBJECTIVE
  To quantify potential benefits of CTV-to-PTV margin reduction for SBRT of liver tumours, as allowed by enhanced treatment precision.
  
  
  METHODS
  For 14 patients plans were generated for the clinical margin and for 3 tighter margins. An in-house developed algorithm was used to optimise beam directions, shapes, and weights for generation of the plan with the highest isocenter dose (D(iso)), while keeping the minimum PTV dose at least 65%xD(iso) and strictly adhering to all imposed hard OAR constraints. Each plan contains 10 optimal beam directions, automatically selected from up to 252 coplanar and non-coplanar input directions.
  
  
  RESULTS
  Apart from the expected tumour dose escalation (D(iso), EUD(PTV), gEUD(PTV)) with decreasing margin, a simultaneous improved sparing of the normal liver (D33%, D50%, D(mean)) was also observed. The smaller the margin was, the bigger both effects were. For renormalized plans with D(iso) equal to the clinical value (3x19.2Gy), and a margin reduction of 50% (2.5mm laterally, 5mm longitudinally), normal liver D33% and D50% reduced on average by 22% (maximum 38%), and 26% (maximum 47%), respectively.
  
  
  CONCLUSIONS
  Using an algorithm for beam direction, shape and weight optimisation, large increases in the therapeutic ratio of liver plans could be obtained for reduced margins.
authors: Department of Radiation Oncology, Erasmus MC - Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. silvia.molinelli@pv.infn.it
authors: Silvia
authors: S
authors: Molinelli
authors: Jacco
authors: J
authors: de Pooter
authors: Alejandra
authors: A
authors: Méndez Romero
authors: Wouter
authors: W
authors: Wunderink
authors: Mauro
authors: M
authors: Cattaneo
authors: Riccardo
authors: R
authors: Calandrino
authors: Ben
authors: B
authors: Heijmen
mesh_terms: D000465:Algorithms; D006801:Humans; D008099:Liver / Q000528:radiation effects; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed