Evaluation of a synthetic single‐crystal diamond detector for relative dosimetry on the Leksell Gamma Knife Perfexion radiosurgery system

Abstract

Purpose: To evaluate the new commercial PTW-60019 synthetic single-crystal microDiamond detector (PTW, Freiburg, Germany) for relative dosimetry measurements on a clinical Leksell Gamma Knife Perfexion radiosurgery system. Methods: Detector output ratios (DORs) for 4 and 8 mm beams were measured using a micro- Diamond (PTW-60019), a stereotactic unshielded diode [IBA stereotactic field detector (SFD)], a shielded diode (IBA photon field detector), and GafChromic EBT3 films. Both parallel and transversal acquisition directions were considered for PTW-60019 measurements. Measured DORs were compared to the new output factor reference values for Gamma Knife Perfexion (0.814 and 0.900 for 4 and 8 mm, respectively). Profiles in the three directions were also measured for the 4 mm beam to evaluate full width at half maximum (FWHM) and penumbra and to compare them with the corresponding Leksell GammaPlan profiles. Results: FWHM and penumbra for PTW-60019 differed from the calculated values by less than 0.2 and 0.3 mm, for the parallel and transversal acquisitions, respectively. GafChromic films showed FWHM and penumbra within 0.1 mm. The output ratio obtained with the PTW-60019 for the 4 mm field was 1.6% greater in transverse direction compared to the nominal value. Comparable differences up to 0.8% and 1.0% for, respectively, GafChromic films and SFD were found. Conclusions: The microDiamond PTW-60019 is a suitable detector for commissioning and routine use of Gamma Knife with good agreement of both DORs and profiles in the three directions

An experimental extrapolation technique using the Gafchromic EBT3 film for relative output factor measurements in small x-ray fields

“…The PTW 60019 microDiamond detector has been extensively studied for small field dosimetry. [24][25][26][27][28]37,38 For the 4 mm diameter cone used in this study, the ROF calculated using the zero area extrapolation technique was in good agreement to the ROF measured with the microDiamond detector. As such, we believe this agreement shows the suitability of using a zero area technique for these smaller fields in film dosimetry.…”

“…A best fit extrapolation technique was applied to the results to determine the zero area output factor utilizing a second order polynomial or linear function based on cone size and data requirements. Relative output factor measurements determined with a PTW 60019 microDiamond detector [24][25][26][27][28] (PTW, PTW-Freiburg, Germany) have also been included for comparison with the extrapolated Gafchromic EBT3 results. These measurements were made under the same geometrical conditions as the measurements for the Gafchromic EBT3 film.…”

Small field dosimetry: What have we learnt?

“…Several recent publications comparing detectors for use for Gammaknife beam dosimetry have recommended use of the IBA SFD, the PTW microDiamond and Gafchromic radiochromic film as the detectors of choice for fields down to 4 mm diameter. (38) …”

Comments on the TRS‐483 protocol on small field dosimetry

“…Similar discrepancies [ Fig. 1(b)] exist between recommended microDiamond k f clin ;f msr Q clin ;Q msr factors for CyberKnife compared to the data from a large collaborative study involving [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] institutions and several microDiamonds. [5][6][7] The error bars are shown if such data exist in the publications.…”

“…11,12 Due to slight modifications of the detector housing between prototype and final product, it is not clear if the prototypes show exactly identical small field correction factors compared to the final commercial product. [13][14][15][16][17][18][19] Figure 1 data can be divided into two groups, one showing k f clin ;f msr Q clin ;Q msr <1.0 and the other >1.0. This behavior is related to the density perturbation effect and volume averaging of microdetector response that have been described in detail in the literatures.…”