Abstract
Background: It worth to be mentioned that the use of small size photon beam is frequently used in modern radio-therapy to treat brain tumors and functional disorders.
Aim of Study: To measure output factors (OFs) and cal-culate the field factor ( ƒclin, ƒmsr ) of small fields and
V clin, Qmse
study its suitability for small field relative dosimetry.
Material and Methods: Numerous detectors were used for measuring the output factors for 6 MV photon beams by a CyberKnife®. To normalize different detector responses for the same field configuration, a correction factor was calculated for each detector by simulating the radiation delivery using Monte Carlo (MC) methods. Detectors used in the study were PTW60019 MicroDiaond, PTW 60018 Silicon diode, PTW31018 MicroLion, and Exradin W1 Scintillator. Field factors were calculated using Alfonso formula. Output factors for a CyberKnife were measured in circular fields with the diameters range from 5mm to 60mm. Measurements were made in a water tank at a 1.5cm in term of depth and at 80 cm for source-to-axis distance.
Results: The results of the current study show that the output measured by the detectors Micro Diamond and Exradin W1 Scintillator (PSD) were within the uncertainties of the Monte Carlo simulations for all the beam cones. The silicon diode detector was over-responding, while the MicroLion was under-responding. We found that an accurate dosimeter could be the MicroDiamond and Exradin W1 Scintillators in small field dosimetry.
Conclusion: We found that at small collimator settings only the synthetic microdiamond (PTW60019) and Exradin W1 scintillation detectors can be used as relative dosimeters without applying any correction factor.