title: Therapeutic benefits in grid irradiation on Tomotherapy for bulky, radiation-resistant tumors.
abstract: BACKGROUND
  Spatially fractionated radiation therapy (SFRT or grid therapy) has proven to be effective in management of bulky tumors. The aim of this project is to study the therapeutic ratio (TR) of helical Tomotherapy (HT)-based grid therapy using linear-quadratic cell survival model.
  
  
  METHODS
  HT-based grid (or HT-GRID) plan was generated using a patient-specific virtual grid pattern of high-dose cylindrical regions using MLCs. TR was defined as the ratio of normal tissue surviving fraction (SF) under HT-GRID irradiation to an open debulking field of an equivalent dose that result in the same tumor cell SF. TR was estimated from DVH data on ten HT-GRID patient plans with deep seated, bulky tumor. Dependence of the TR values on radiosensitivity of the tumor cells and prescription dose was analyzed.
  
  
  RESULTS
  The mean ± standard deviation (SD) of TR was 4.0 ± 0.7 (range: 3.1-5.5) for the 10 patients with single fraction maximum dose of 20 Gy to GTV assuming a tumor cell SF at 2 Gy (SF2t) value of 0·5. In addition, the mean ± SD of TR values for SF2tvalues of 0.3 and 0.7 were found to be 1 ± 0.1 and 18.0 ± 5.1, respectively. Reducing the prescription dose to 15 and 10 Gy lowered the respective TR values to 2.0 ± 0.2 and 1.2 ± 0.04 for a SF2tvalue of 0.5.
  
  
  CONCLUSIONS
  HT-GRID therapy demonstrates a significant therapeutic advantage over uniform dose from an open field irradiation for the same tumor cell kill. TR increases with the radioresistance of the tumor cells and with prescription dose.
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Narayanasamy
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: b Comprehensive Cancer Center of Nevada , Las Vegas , NV , USA.|c Department of Radiation Oncology , University of Nevada Las Vegas , NV , USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Meigooni
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Nava
authors.initials: N
authors.lastname: Paudel
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Morrill
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Maraboyina
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Loverd
authors.initials: L
authors.lastname: Peacock
authors.affiliation: a Department of Radiation Oncology , University of Arkansas for Medical Sciences , Little Rock , AR , USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Penagaricano
mesh_terms: D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000532:radiotherapy*; D011836:Radiation Tolerance / Q000528:radiation effects*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies