Characterization of a microSilicon diode detector for small-field photon beam dosimetry.

Kazuhiko Ogawa,Masateru Fujiwara,Keisuke Tamari,Fumiaki Isohashi,Yuji Seo,Keita Okamura,Hirokazu Mizuno,Yuichi Akino,Osamu Suzuki,Hiroya Shiomi

doi:10.1093/jrr/rraa010

Kazuhiko Ogawa, Masateru Fujiwara + Show 8 more

Open Access

https://doi.org/10.1093/jrr/rraa010

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Abstract

This study characterized a new unshielded diode detector, the microSilicon (model 60023), for small-field photon beam dosimetry by evaluating the photon beams generated by a TrueBeam STx and a CyberKnife. Temperature dependence was evaluated by irradiating photons and increasing the water temperature from 11.5 to 31.3°C. For Diode E, microSilicon, microDiamond and EDGE detectors, dose linearity, dose rate dependence, energy dependence, percent-depth-dose (PDD), beam profiles and detector output factor (OFdet) were evaluated. The OFdet of the microSilicon detector was compared to the field output factors of the other detectors. The microSilicon exhibited small temperature dependence within 0.4%, although the Diode E showed a linear variation with a ratio of 0.26%/°C. The Diode E and EDGE detectors showed positive correlations between the detector reading and dose rate, whereas the microSilicon showed a stable response within 0.11%. The Diode E and microSilicon demonstrated negative correlations with the beam energy. The OFdet of microSilicon was the smallest among all the detectors. The maximum differences between the OFdet of microSilicon and the field output factors of microDiamond were 2.3 and 1.6% for 5 × 5 mm2 TrueBeam and 5 mm φ CyberKnife beams, respectively. The PDD data exhibited small variations in the dose fall-off region. The microSilicon and microDiamond detectors yielded similar penumbra widths, whereas the other detectors showed steeper penumbra profiles. The microSilicon demonstrated favorable characteristics including small temperature and dose rate dependence as well as the small spatial resolution and output factors suitable for small field dosimetry.

Highlights

Small field dosimetry has become increasingly important as advanced radiotherapy techniques including stereotactic radiotherapy (SRT), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), are used more commonly around the world
We report on the characteristics of the microSilicon diode detector for small-field photon beam dosimetry
We demonstrated that the microSilicon detector yields stable responses in a wide range of water temperatures, whereas the Diode E detector showed a 0.26%/◦C

Summary

Introduction

Small field dosimetry has become increasingly important as advanced radiotherapy techniques including stereotactic radiotherapy (SRT), intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), are used more commonly around the world. Several types of detectors (e.g. diodes, diamond and plastic scintillators) have been developed to minimize these effects [5,6,7,8]. P-type silicon diode detectors are often used to conduct scanning and non-scanning measurements for beam data commissioning. The diode detectors have small sensitive volumes, which can minimize the volume averaging effects [9, 10]. Diode detectors have some disadvantageous characteristics for accurate dosimetry, such as temperature, dose rate and energy dependences [11,12,13]. Diode detectors over-respond to low-energy photon beams because of the photoelectric effects in silicon [14, 15]

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