A synthetic diamond diode in volumetric modulated arc therapy dosimetry

Abstract

Purpose: The aim of this work is to investigate the behavior of a single crystal diamond diode (SCDD) for volumetric modulated arc therapy (VMAT) dose verifications. This delivery technique is one of the most severe test of a dosimeter performance due to the modulation of the dose rate achieved by simultaneously changing the velocity of the gantry and the position of the collimator leaves. The performed measurements with VMAT photon beams can therefore contribute to an overall global validation of the device to be used in dose distribution verifications. Methods:The SCDD response to 6 MVRX has been tested and compared with reference ionization chambers and treatment planning system (TPS) calculations in different experiments: (a) measurements of output factors for small field sizes (square fields of side ranging between 8 mm and 104 mm) by SCDD and A1SL ionization chamber; (b) angular dependence evaluation of the entire experimental set-up by SCDD, A1SL, and Farmer ionization chambers; and (c) acquisition of dose profiles for a VMAT treatment of a pulmonary disease in latero-lateral and gantry-target directions by SCDD and A1SL ionization chamber. Results: The output factors measured by SCDD favorably compare with the ones obtained by A1SL, whose response is affected by the lack of charged particle equilibrium and by averaging effect when small fields are involved. From the experiment on angular dependence, a good agreement is observed among the diamond diode, the ion chambers, and the TPS. In VMAT profiles, the absorbed doses measured by SCDD and A1SL compare well with the TPS calculated ones. An overall better agreement is observed in the case of the diamond dosimeter, which is also showing a better accuracy in terms of distance to agreement in the high gradient regions. Conclusions: Synthetic diamond diodes, whose performance were previously studied for conformal and IMRT radiotherapy techniques, were found to be suitable detectors also for dosimetric measurements in volumetric arc therapy treatments.

Evaluation of a synthetic single-crystal diamond detector for relative dosimetry measurements on a CyberKnife™

“…The use of research SCDDs has been reported [6][7][8] in conjunction with conventional linear accelerators, with square field sizes from 100 3 100 mm 2 down to 10 3 10 mm 2 as a measured at a 1000-mm source-to-detector distance (SDD). In this work, we present the results using a dedicated stereotactic linear accelerator with circular fields for fixed collimators ranging from 5 to 60 mm, at a nominal SDD of 800 mm, in a 6-MV unflattened photon beam.…”

Evaluation of the dose calculation accuracy for small fields defined by jaw or MLC for AAA and Acuros XB algorithms

“…No voltage bias is required and the diamond operates as a Schottky diode. [30][31][32][33][34] The set of measurements consisted in point data acquisition, on the beam central axis at isocenter at 10 cm depth (source to surface distance SSD = 90 cm). Precise positioning of the detector on the beam central axis was guaranteed by centering the system according to the profiles acquired along the main axes at the measuring depth.…”

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

“…[15][16][17][18] The microDiamond active volume is composed of a 1 µm thick intrinsic diamond layer, with a 1 mm radius and a total sensitive volume of 0.004 mm 3 . The effective point of measurement is 1 mm from the housing surface.…”

“…The characteristics of the synthetic diamond detector (PTW-60019), such as small active volume (0.004 mm 3 ), near water-equivalence (Z eff = 6), and low energy dependence, make it an interesting candidate for small field dose measurements as demonstrated by many authors. [15][16][17][18][19] To our knowledge, no one demonstrated the feasibility of using this synthetic diamond for OFs measurement for LGKP. Profiles in the three directions were also measured for the 4 mm collimator.…”