title: Dosimetric characteristics of a newly designed grid block for megavoltage photon radiation and its therapeutic advantage using a linear quadratic model.
abstract: Grid radiation therapy with megavoltage x-ray beam has been proven to be an effective technique for management of large, bulky malignant tumors. The clinical advantage of GRID therapy, combined with conventional radiation therapy, has been demonstrated using a prototype GRID block [Mohiuddin, Curtis, Grizos, and Komarnicky, Cancer 66, 114-118 (1990)]. Recently, a new GRID block design with improved dosimetric properties has become commercially available from Radiation Product Design, Inc. (Albertive, MN). This GRID collimator consists of an array of focused apertures in a cerrobend block arranged in a hexagonal pattern having a circular cross-section with a diameter and center-to-center spacing of 14.3 and 21.1 mm, respectively, in the plane of isocenter. In this project, dosimetric characteristics of the newly redesigned GRID block have been investigated for a Varian 21EX linear accelerator (Varian Associates, Palo Alto, CA). These determinations were performed using radiographic films, thermoluminescent dosimeters in Solid Water phantom materials, and an ionization chamber in water. The output factor, percentage depth dose, beam profiles, and isodose distributions of the GRID radiation as a function of field size and beam energy have been measured using both 6 and 18 MV x-ray beams. In addition, the therapeutic advantage obtained from this treatment modality with the new GRID block design for a high, single fraction of dose has been calculated using the linear quadratic model with alpha/beta ratios for typical tumor and normal cells. These biological characteristics of the new GRID block design will also be presented.
authors.affiliation: University of Kentucky Chandler Medical Center, Department of Radiation Medicine, Lexington, Kentucky 40536-0084, USA. alimeig@uky.edu
authors.forename: Ali S
authors.initials: AS
authors.lastname: Meigooni
authors.forename: Kai
authors.initials: K
authors.lastname: Dou
authors.forename: Navid J
authors.initials: NJ
authors.lastname: Meigooni
authors.forename: Michael
authors.initials: M
authors.lastname: Gnaster
authors.forename: Shahid
authors.initials: S
authors.lastname: Awan
authors.forename: Sharifeh
authors.initials: S
authors.lastname: Dini
authors.forename: Ellis L
authors.initials: EL
authors.lastname: Johnson
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D016014:Linear Models; D008954:Models, Biological; D009369:Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D017785:Photons / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods; D014407:Tumor Cells, Cultured