Feasibility study of using Stereotactic Field Diode for field output factors measurement and evaluating three new detectors for small field relative dosimetry of 6 and 10 MV photon beams

Abstract

This study assesses the feasibility of using stereotactic field diode (SFD) as an alternate to gaf chromic films for field output factor (FF) measurement and further evaluating three new detectors for small field dosimetry. Varian 21EX linear accelerator was used to generate 6 and 10 MV beams of nominal square fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. One passive (EBT3 films) and five active detectors including IBA RAZOR diode(RD), SFD, RAZOR nanochamber (RNC), pinpoint chamber (PTW31023), and semiflex chamber (PTW31010) were employed. FFs were measured using films and SFD while beam profiles and percentage depth dose (PDD) distribution were acquired with active detectors. Polarity (kpol) and recombination (ks) effects of ion chambers were determined and corrected for output ratio measurement. Correction factors (CF) of RD, RNC, and PTW31023 in axial and radial orientation were also measured. Stereotactic field diode measured FFs have shown good agreement with films (with difference of <1%). RD and RNC measured beam profiles were within 3% deviation from the SFD values. Variation in kpol with field size for RNC and PTW31023 was up to 4% and 0.4% (for fields ≥ 1 × 1 cm2), respectively, while variation in ks of PTW31023 was <0.2 %. The maximum values of CF have been calculated to be 5.2%, 2.0%, 13.6%, and 25.5% for RD, RNC, PTW31023‐axial, and PTW31023‐radial respectively. This study concludes that SFD with appropriate CFs as given in TRS 483 may be used for measuring FFs as an alternate to EBT3 films. Whereas RD and RNC may be used for beam profile and PDD measurement in small fields. Considering the limit of usability of 2%, RNC may be used without CF for FF measurement in the smallfields investigated in this study.

Determination of correction factors in small MLC‐defined fields for the Razor and microSilicon diode detectors and evaluation of the suitability of the IAEA TRS‐483 protocol for multiple detectors

“…The Razor correction factors showed a larger range of disagreement with the literature than the microSilicon. The largest difference was 2.9% to Gul et al 9 . for a 0.5 × 0.5 cm 2 field size.…”

“…The microSilicon correction factors for 6-MV show a maximum difference of 1.6% for a 0.5 × 0.5 cm 2 field size to Schönfeld et al 3 and less than 0.7% to all field sizes of Weber et al 5 The Razor correction factors showed a larger range of disagreement with the literature than the microSilicon. The largest difference was 2.9% to Gul et al 9 for a 0.5 × 0.5 cm 2 field size. Our correction factors agreed more closely with Caser et al, 8 with agreement ranging between −1.5% and 2.0%.…”

“…A comparison to correction factors from the literature for the microSilicon 3,5 and Razor 8,9 is shown in Figures 5-9. No data for 6-FFF, 10-MV, and 10-FFF was in the literature to compare against microSilicon correction factors from this work.…”

“…. Moreover, Liu et al., 7 Casar et al., 8 and Gul et al 9 . have determined small MLC field correction factors for the Razor detector using experimental methods for both 6‐MV and 10‐MV photon energies.…”

“…Its suitability for small field dosimetry and superiority to its predecessor IBA SFD have been investigated by Reggiori et al 6 . Moreover, Liu et al, 7 Casar et al, 8 and Gul et al 9 have determined small MLC field correction factors for the Razor detector using experimental methods for both 6-MV and 10-MV photon energies. Other studies have assessed the Razor for measuring cone output factors or factors for the CyberKnife system.…”