title: Red shell: defining a high-risk zone of normal tissue damage in stereotactic body radiation therapy.
abstract: OBJECTIVE
  To define a volume of tissue just outside of the clinical target volume (CTV) or planning target volume (PTV) in stereotactic body radiation therapy (SBRT) that receives doses appreciably above the tolerance level and in which other critical tissue structures must be avoided.
  
  
  METHODS
  We define the tissue between the borders of the CTV and PTV as the Inner Red Shell. The tissue surrounding the PTV that receives higher than the local tissue tolerance is defined as the Outer Red Shell. Contributing factors to the volume of the Red Shell include the prescription dose, dose gradient and PTV size, together with the type of tissue and its tolerance are discussed. An illustrative example and two clinical cases are reported.
  
  
  RESULTS
  The volume of Red Shell increases with higher prescription dose, slower dose fall-off, larger PTV volume, and higher tissue radiosensitivity. Avoidance of proximal critical serial organs may alter the volume and shape of the Red Shell after repeated, detailed treatment planning.
  
  
  CONCLUSIONS
  Rather than defining tolerance and toxicity as simply a dose level received by the tissues, the volume of tissue receiving risk levels above tolerance can be quantified as the "cost" of SBRT. This concept may be adopted in other techniques offering ablative and high-dose gradients. Further consideration should be given to collecting clinical data for refining the choice of constraint doses, especially in parts of the brain, lung, liver, and kidney.
authors.affiliation: Philadelphia CyberKnife, Havertown, PA 19083, USA. JunBME@yahoo.com
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Jack F
authors.initials: JF
authors.lastname: Fowler
authors.forename: John P
authors.initials: JP
authors.lastname: Lamond
authors.forename: Rachelle
authors.initials: R
authors.lastname: Lanciano
authors.forename: Jing
authors.initials: J
authors.lastname: Feng
authors.forename: Luther W
authors.initials: LW
authors.lastname: Brady
mesh_terms: D006801:Humans; D016014:Linear Models; D008099:Liver / Q000000981:diagnostic imaging / Q000528:radiation effects; D011832:Radiation Injuries / Q000000981:diagnostic imaging / Q000473:pathology; D011836:Radiation Tolerance; D011859:Radiography; D016634:Radiosurgery / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012062:Relative Biological Effectiveness