title: Beam configuration and physical parameters of clinical high energy photon beam for total body irradiation (TBI).
abstract: OBJECTIVE
  To start total body irradiation (TBI) treatments, physical parameters are measured for a magna field irradiation.
  
  
  METHODS
  6 MV photon beam from Clinac 600 CD linear accelerator (Varian, USA) with fully opened collimator at 45° and gantry at 270° provided a diamond shaped magna field with diagonal dimension 224 cm at 4.0 m source skin distance (SSD). The flatness of the radiation field was measured in the presence of locally designed acrylic beam spoiler and beam flatness filter. Central Axis Depth dose data (CADD), tissue maximum ratios and entrance dose pattern are measured using large phantoms. Methods for clinical dose estimation using semi-conductor diodes and TLD were standardized.
  
  
  RESULTS
  PVC beam flattener at the shielding tray position and the presence of acrylic beam spoiler in the radiation field provided a flatness of 100.15% ± 0.44% compared to open beam flatness 101.6 ± 1.5%. A reduction of 2% in percentage depth dose was observed at 10 cm depth in the presence of 15 mm acrylic beam spoiler. However, no changes are observed in the TMRs with presence of beam spoiler. The measured ionization ratios clearly showed change of beam quality with the introduction of beam spoiler. The presence of 15 mm beam spoiler ensured entrance dose 100% at skin and remaining unchanged within 1% upto a depth of 10 mm. Phantom measurements show good agreement between calculated and measured doses.
  
  
  CONCLUSIONS
  The paper recommends use of modified CADD parameters for treatment planning, if calibration of output is carried out in the presence of beam spoiler.
authors.affiliation: Medical Physics Unit, Oman. ravichandranrama@rediffmail.com
authors.forename: Ramamoorthy
authors.initials: R
authors.lastname: Ravichandran
authors.forename: Johnson Pichi
authors.initials: JP
authors.lastname: Binukumar
authors.forename: Chirayathmanjiyil Antony
authors.initials: CA
authors.lastname: Davis
authors.forename: Somangali Sathiyamurthy
authors.initials: SS
authors.lastname: Sivakumar
authors.forename: Kammari
authors.initials: K
authors.lastname: Krishnamurthy
authors.forename: Zahid Al
authors.initials: ZA
authors.lastname: Mandhari
authors.forename: Balakrishnan
authors.initials: B
authors.lastname: Rajan
mesh_terms: D002138:Calibration; D006801:Humans; D007938:Leukemia / Q000532:radiotherapy*; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D014916:Whole-Body Irradiation / Q000295:instrumentation / Q000379:methods*