title: Forward versus inverse planning in oropharyngeal cancer: A comparative study using physical and biological indices.
abstract: BACKGROUND
  Possible benefits of inverse planning.
  
  
  OBJECTIVE
  To analyze possible benefits of inverse planning intensity modulated radiation therapy (IMRT) over field-in-field 3D conformal radiation therapy (FIF-3DCRT) and to evaluate the differences if any, between low (6 Million Volts) and high energy (15 Million Volts) IMRT plans.
  
  
  METHODS
  Ten patients with squamous cell carcinoma of oropharynx, previously treated with 6 MV step and shoot IMRT were studied. V100, V33, V66 , mean dose and normal tissue complication probabilities (NTCP) were evaluated for parotid glands. Maximum dose and NTCP were the parameters for spinal cord.
  
  
  METHODS
  A two-tailed t-test was applied to analyze statistical significance between the different techniques.
  
  
  RESULTS
  For combined parotid gland, a reduction of 4.374 Gy, 9.343 Gy and 7.883 Gy were achieved for D100, D66 and D33, respectively in 6 MV-IMRT when compared with FIF-3DCRT. Spinal cord sparing was better in 6 MV-IMRT (40.963 ± 2.650), with an average reduction of maximum spinal cord dose by 7.355 Gy from that using the FIF-3DCRT technique. The uncomplicated tumor control probabilities values were higher in IMRT plans thus leading to a possibility of dose escalation.
  
  
  CONCLUSIONS
  Though low-energy IMRT is the preferred choice for treatment of oropharyngeal cancers, FIF-3DCRT must be given due consideration as a second choice for its well established advantages over traditional conventioan technique.
authors.affiliation: Department of Radiation Oncology, Valavadi Narayanaswamy Cancer Centre, G. Kuppuswamy Naidu Memorial Hospital, Coimbatore, India.
authors.forename: T
authors.initials: T
authors.lastname: Sundaram
authors.forename: M
authors.initials: M
authors.lastname: Nagarajan
authors.forename: V
authors.initials: V
authors.lastname: Nagarajan
authors.forename: Sanjay S
authors.initials: SS
authors.lastname: Supe
authors.forename: R
authors.initials: R
authors.lastname: Mohanraj
authors.forename: T
authors.initials: T
authors.lastname: Balaji
authors.forename: S
authors.initials: S
authors.lastname: Jayakumar
authors.forename: M
authors.initials: M
authors.lastname: Balasubramaniam
authors.forename: K N
authors.initials: KN
authors.lastname: Govindarajan
mesh_terms: D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009367:Neoplasm Staging; D009959:Oropharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies