Evaluation of the IAEA‐TRS 483 protocol for the dosimetry of small fields (square and stereotactic cones) using multiple detectors

Abstract

The IAEA TRS 483 protocol1 for the dosimetry of small static fields in radiotherapy was used to calculate output factors for the Elekta Synergy linac at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Small field output factors for both square and circular fields were measured using nine different detectors. The “corrected” output factors (ratio of detector readings multiplied by the appropriate correction factor from the protocol) showed better consistency compared to the “uncorrected” output factors (ratio of detector readings only), with the relative standard deviation decreasing by approximately 1% after the application of the relevant correction factors. Comparisons relative to an arbitrarily chosen PTW 60019 microDiamond detector showed a reduction of maximal variation for the corrected values of approximately 3%. A full uncertainty budget was prepared to analyze the consistency of the output factors. Agreement within uncertainties between all detectors and field sizes was found, except for the 15 mm circular field. The results of this study show that the application of IAEA TRS 4831 when measuring small fields will improve the consistency of small field measurements when using multiple detectors contained within the protocol.

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 application of TRS‐483 correction factors reduced the variation in measured output factors between the six individual detectors in this study, with the exceptions of the PTW 60016 diode for 6‐MV and 6‐FFF beams and the IBA PFD3G for 10‐MV and 10‐FFF beams. This agrees with the work of Smith et al 12 . who found that the PTW 60016 diode corrected output factors were lower than the average of other detectors for a 15 mm cone.…”

“…The corrected output factors measured with the other five detectors agreed well. This follows the results of Smith et al., 12 who found that TRS‐483 correction factors reduced the variation in output factors for a variety of detectors. The application of TRS‐483 correction factors to small field measurements is a valid method to determine accurate output factors, however multiple detectors should be used to reduce the uncertainty of the results and limit the effect of variation amongst individual detectors.…”

“…The uncertainties due to output constancy and effect of FWHM on K TRS‐483 are small compared to the other uncertainties discussed. The total relative standard uncertainty for detector measurements was similar to the values found by Smith et al 12 ,. with a maximum difference of 0.3% for 1 × 1 cm 2 field size for unshielded diodes/microDiamond.…”

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

“…Besides the historical firm [28] it should be underlined that the number of vendors, such as [29][30][31] has increased in the past decade. The next important development is the growing diffusion of a commercial dosimeter, the PTW60019 microDiamond, which has become a reference dosimeter after many comparative studies with other types of dosimeters [32][33][34][35][36].…”

Development of an independent MU calculation software for radiotherapy treatments with stereotactic cones

“…To ensure that the StereoCalc is truly independent, a set of relative measurements including multiple depth dose curves and output factors (OFs) were obtained, following the new dosimetry formalism proposed by the International Atomic Energy Agency TRS‐483: dosimetry of small static fields used in external beam radiotherapy. 8 , 9 This is the first international code of practice dedicated to the dosimetry of small fields for specialized radiotherapy equipment able to produce small fields and for conventional LINACs with and without flattening filter for photon fields up to 10 MV.…”