Comparative Study of Output Factors of Small Field Sizes Dosimetry Systems

PAOLO FRANCESCON, Ph.D., SAMAH K. ELSHAMNDY, M.Sc.;; CHIARA ORLANDI, Ph.D., NINFA SATARIANO, Ph.D.;; AHMED M. AHMED, Ph.D., HASSAN ABOUELENEIN, Ph.D.;

doi:10.21608/mjcu.2019.59512

Comparative Study of Output Factors of Small Field Sizes Dosimetry Systems

Document Type : Original Article

Authors

10.21608/mjcu.2019.59512

Abstract

Abstract
Background: The use of small fields in radiotherapy techniques has swiftly increased, in detail in stereotactic treatments and large uniform or nonuniform fields, which are composed of small fields such as for intensity-modulated radiation therapy (IMRT).
Aim of Study: Compare output factors (OFs) of small fields using various detectors and investigate its suitability for small field relative and absolute dosimetry through explor-ing the measured OFs with implementation to 6 MV photon beams by a Cyber Knife®. Normalization of different detector responses for the same field configuration is accomplished via applying a Monte Carlo derived correction factor.
Materials and Methods: Detectors used in the study were PTW60019 MicroDiaond, Exradin W1 Scintillator, and CCO1 IBA ion chamber, and field factors were calculated using Alfonso formula. OFs for a CyberKnife were measured in circular fields with the diameters range from 5mm to 60mm and using water tank at a 1.5cm depth and at 80cm source-to-axis distance.
Results: The OFs measured by Micro Diamond and Exra-din W1 (PSD) were within the uncertainties of the M.C. simulations for all the beam cones. While the CCO1 IBA ion chamber was unstable responding.
Conclusion: PTW 60019 microdiamond and Exradin W1 provide a useful and possibly superior alternative to existing dosimetry systems for small fields, as they are inherently less susceptible to volume-averaging and perturbation effects than larger, air-filled ionization chambers. Ultimately, they are favorable in small-field dosimetries.

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