Small field output correction factors of the microSilicon detector and a deeper understanding of their origin by quantifying perturbation factors

Weber, Carolin; Kranzer, Rafael; Weidner, Jan; Kroeninger, K.; Poppe, Björn; Looe, Hui Khee; Poppinga, Daniela

doi:10.1002/mp.14149

Cited by 22 publications

(35 citation statements)

References 32 publications

(73 reference statements)

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“…An unmodified 60023‐type diode was tested along with variants containing airgaps of thickness 0.6, 0.8, and 1.0 mm. The outer casings of the detectors included RW3 plastic caps 12 . Airgaps were built directly into these caps in modified diodes, keeping the thickness of RW3 above the airgaps equal to that in the unmodified detector.…”

Section: Methodsmentioning

confidence: 99%

“…The outer casings of the detectors included RW3 plastic caps. 12 Airgaps were built directly into these caps in modified diodes, keeping the thickness of RW3 above the airgaps equal to that in the unmodified detector.…”

Section: Ptw 60023-type Microsilicon Detectorsmentioning

confidence: 99%

“…The 60023‐type diode has been tested in 6 MV fields ≥ 0.5 × 0.5 cm 2 by Schönfeld et al 11 . and Weber et al., 12 who characterized its response on‐axis at 10 cm depth in water and off‐axis at 5 cm depth. Compared to the 60017‐type diode, the new detector required small field correction factors closer to unity.…”

Section: Introductionmentioning

confidence: 99%

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The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation

Georgiou

Würfel²,

Gilmore

et al. 2021

Medical Physics

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Purpose:We have experimentally and computationally characterized the PTW microSilicon 60023-type diode's performance in 6 and 15 MV photon fields ≥5 × 5 mm 2 projected to isocenter. We tested the detector on-and off -axis at 5 and 15 cm depths in water, and investigated whether its response could be improved by including within it a thin airgap. Methods: Experimentally, detector readings were taken in fields generated by a Varian TrueBeam linac and compared with doses-to-water measured using Gafchromic film and ionization chambers. An unmodified 60023-type diode was tested along with detectors modified to include 0.6, 0.8, and 1.0 mm thick airgaps. Computationally, doses absorbed by water and detectors' sensitive volumes were calculated using the EGSnrc/BEAMnrc Monte Carlo radiation transport code. Detector response was characterized using k, a factor that corrects for differences in the ratio of dose-to-water to detector reading between small fields and the reference condition,in this study 5 cm deep on-axis in a 4 × 4 cm 2 field. Results: The greatest errors in measurements of small field doses made using uncorrected readings from the unmodified 60023-type detector were overresponses of 2.6% ± 0.5% and 5.3% ± 2.0% determined computationally and experimentally, relative to the reading-per-dose in the reference field. Corresponding largest errors for the earlier 60017-type detector were 11.9% ± 0.6% and 11.7% ± 1.4% over-responses. Adding even the thinnest, 0.6 mm, airgap to the 60023-type detector over-corrected it, leading to under-responses of up to 4.8% ± 0.6% and 5.0% ± 1.8% determined computationally and experimentally. Further, Monte Carlo calculations indicate that a detector with a 0.3 mm airgap would read correctly to within 1.3% on-axis. The ratio of doses at 15 and 5 cm depths in water in a 6 MV 4 × 4 cm 2 field was measured more accurately using the unmodified 60023-type detector than using the 60017-type detector, and was within 0.3% of the ratio measured using an ion chamber. The 60023type diode's sensitivity also varied negligibly as dose-rate was reduced from 13 to 4 Gy min -1 by decreasing the linac pulse repetition frequency, whereas the sensitivity of the 60017-type detector fell by 1.5%. Conclusions: The 60023-type detector performed well in small fields across a wide range of beam energies, field sizes, depths, and off -axis positions. Its response can potentially be further improved by adding a thin, 0.3 mm, airgap.

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Section: Methodsmentioning

confidence: 99%

Section: Ptw 60023-type Microsilicon Detectorsmentioning

confidence: 99%

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The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation

Georgiou

Würfel²,

Gilmore

et al. 2021

Medical Physics

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“…Recently, a new unshielded silicon diode detector (PTW-60023) known as a microSilicon detector with very small dimension (0.032 mm 3 with 1.5 mm diameter) with an epoxy density of 1.15 g/cm 3 was introduced and was found to have very suitable characteristics for small-field dosimetry for both linear accelerators and CyberKnife. [156][157][158][159] Even the new shielded diode (PTW-60022) showed a very good characteristics and superior results in very small photon fields. 160…”

Section: Diode Typesmentioning

confidence: 99%

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

et al. 2021

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Abbreviations: %dd(10) x , The photon component of the percent depth dose at 10 cm depth in water for a 10 cm 2 × 10 cm 2 field; L∕ w air , Restricted mass collision stopping power ratio of water to air; en ∕ , Spectrum-averaged mass energy-absorption coefficient; AAPM, American Association of Physicists in Medicine; CPE, Charged Particle Equilibrium; DLG, Dosimetric leaf gap; D f msr w,Q msr , Absorbed dose to water at the reference depth z ref in water in the absence of the detector in a field specified by f msr and beam quality Q msr .; f clin , Clinical (clin) non-reference radiation field; f msr , Machine-specific reference (msr) field; f ref , Reference field (ref) specified in dosimetry protocols for which the calibration coefficient of an ionization chamber in terms of absorbed dose to water is provided by a standards laboratory; FWHM, Full-width at half-maximum; GUM, Guide to the expression of Uncertainty in Measurements.; IAEA, International Atomic Energy Agency; ICRU, International Commission on Radiation Units and Measurements; IMRT, Intensity-modulated radiation therapy; k Q,Q 0 , The beam-quality correction factor, which corrects for the differences between the response of an ionization chamber in the reference beam of quality Q o used for calibrating the chamber and the beam of quality Q (defined as k Q . in TG-51 4 ); k f ref Q,Q 0 , Correction factor that accounts for the differences between the response of a detector in field f ref in a beam of quality Q and reference beam quality Q 0 as defined in TRS-483. 1 and Palmans et al 2 ; k fclin,fmsr Qclin,Q msr , The detector-specific correction factor that accounts for the difference between the responses of the detector in fields f clin in a beam of quality Q clin and in fields f msr in beam of quality Q msr as defined by Alfonso et al. 3 ; LCPE, Lateral charged particle equilibrium; M fmsr Qmsr , Detector reading in field f msr and beam quality Q msr corrected for influence of changes in pressure and temperature, incomplete charge collection, polarity effect and electrometer correction factor (TRS-483 1 ); MU, Monitor unit; N D,w,Q 0 , This is N D,w in TG-51, 4 and defined as the calibration coefficient in terms of absorbed dose to water for an ionization chamber at a reference beam of quality,Q 0 and field size f ref ; N f ref D,w,Q 0

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“…The novel PTW microSilicon detector may be an appropriate detector for measurements in high-energy small-field electron beams. The suitability of this small-volume detector for dosimetry in small photon beams was already investigated, showing very good dosimetric properties [8][9][10]. In addition, three-dimensional characterization of the active volumes of the PTW microSilicon has been performed for accurate Monte Carlo simulations of the detector [11].…”

Section: Introductionmentioning

confidence: 99%

Dosimetric Characterization of Small Radiation Therapy Electron Beams Collimated by Tubular Applicators With the New Micro-Silicon Detector

Russo¹,

Bettarini²,

Leonulli³

et al. 2021

Preprint

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High-energy small electron beams generated by linear accelerators are used for radiotherapy of localized superficial tumors. The aim of the present study is to assess the dosimetric performance under small radiation therapy electron beams of the novel PTW microSilicon detector by comparison with commercially available dosimeters. Relative dose measurements of circular fields with 20, 30, 40 and 50 mm aperture diameters were performed for 4 to 12 MeV energy range of electron beams generated by an Elekta Synergy linac. Percentage depth dose, transverse profiles and output factors normalized to the 10 × 10 cm2 reference field were measured. All dosimetric data were collected in a PTW MP3 motorized water phantom at SSD of 100cm by using the novel PTW microSilicon detector. The PTW diode E and the PTW microDiamond were also used in all beam aperture for benchmarking. Data for the biggest field size were also measured by the PTW Advanced Markus ionization chamber.Measurements performed by the microSilicon are in good agreement with the reference values for all the tubular applicators and beam energies, within the stated uncertainties. This confirms the reliability of the microSilicon detector for relative dosimetry of small radiation therapy electron beams collimated by tubular applicators.

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Small field output correction factors of the microSilicon detector and a deeper understanding of their origin by quantifying perturbation factors

Cited by 22 publications

References 32 publications

The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation

The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

Dosimetric Characterization of Small Radiation Therapy Electron Beams Collimated by Tubular Applicators With the New Micro-Silicon Detector

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