title: Dosimetry of cone-defined stereotactic radiosurgery fields with a commercial synthetic diamond detector.
abstract: OBJECTIVE
  Small field x-ray beam dosimetry is difficult due to lack of lateral electronic equilibrium, source occlusion, high dose gradients, and detector volume averaging. Currently, there is no single definitive detector recommended for small field dosimetry. The objective of this work was to evaluate the performance of a new commercial synthetic diamond detector, namely, the PTW 60019 microDiamond, for the dosimetry of small x-ray fields as used in stereotactic radiosurgery (SRS).
  
  
  METHODS
  Small field sizes were defined by BrainLAB circular cones (4-30 mm diameter) on a Novalis Trilogy linear accelerator and using the 6 MV SRS x-ray beam mode for all measurements. Percentage depth doses (PDDs) were measured and compared to an IBA SFD and a PTW 60012 E diode. Cross profiles were measured and compared to an IBA SFD diode. Field factors, ΩQclin,Qmsr (fclin,fmsr) , were calculated by Monte Carlo methods using BEAMnrc and correction factors, kQclin,Qmsr (fclin,fmsr) , were derived for the PTW 60019 microDiamond detector.
  
  
  RESULTS
  For the small fields of 4-30 mm diameter, there were dose differences in the PDDs of up to 1.5% when compared to an IBA SFD and PTW 60012 E diode detector. For the cross profile measurements the penumbra values varied, depending upon the orientation of the detector. The field factors, ΩQclin,Qmsr (fclin,fmsr) , were calculated for these field diameters at a depth of 1.4 cm in water and they were within 2.7% of published values for a similar linear accelerator. The corrections factors, kQclin,Qmsr (fclin,fmsr) , were derived for the PTW 60019 microDiamond detector.
  
  
  CONCLUSIONS
  The authors conclude that the new PTW 60019 microDiamond detector is generally suitable for relative dosimetry in small 6 MV SRS beams for a Novalis Trilogy linear equipped with circular cones.
authors.affiliation: Department of Radiation Oncology, Chris O'Brien Lifehouse, 119-143 Missenden Road, Camperdown, NSW 2050, Australia and School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Level 4 O Block, Garden's Point, Brisbane, QLD 4001, Australia.
authors.forename: Johnny E
authors.initials: JE
authors.lastname: Morales
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Level 4 O Block, Garden's Point, Brisbane, QLD 4001, Australia.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Crowe
authors.affiliation: Department of Radiation Oncology, Chris O'Brien Lifehouse, 119-143 Missenden Road, Camperdown, NSW 2050, Australia.
authors.forename: Robin
authors.initials: R
authors.lastname: Hill
authors.affiliation: Department of Radiation Oncology, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010, Australia.
authors.forename: Nigel
authors.initials: N
authors.lastname: Freeman
authors.affiliation: School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Level 4 O Block, Garden's Point, Brisbane, QLD 4001, Australia.
authors.forename: J V
authors.initials: JV
authors.lastname: Trapp
mesh_terms: D000465:Algorithms; D018130:Diamond / Q000737:chemistry; D006801:Humans; D009010:Monte Carlo Method; D010315:Particle Accelerators; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D014867:Water / Q000737:chemistry; D014965:X-Rays
chemical_list: D014867:Water; D018130:Diamond