Technical Note: Characterization of the new microSilicon diode detector

Schönfeld, Ann-Britt; Poppinga, Daniela; Kranzer, Rafael; Wilde, Rudy Leon De; Willborn, K.; Poppe, Björn; Looe, Hui Khee

doi:10.1002/mp.13710

Cited by 22 publications

(39 citation statements)

References 18 publications

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“…The choice of the reference detector influences directly the results obtained using the deconvolution method. The previous studies 12 , 13 mostly used silicon diodes as a reference, but these are subject to the density effect 15 , 27 in small fields and additionally, in larger depths or field sizes, to energy dependence. In this study, the microDiamond detector with more advantageous properties 14 , 15 , 28 has been chosen as the reference detector to train the NN.…”

Section: Discussionmentioning

confidence: 99%

“…The previous studies 12 , 13 mostly used silicon diodes as a reference, but these are subject to the density effect 15 , 27 in small fields and additionally, in larger depths or field sizes, to energy dependence. In this study, the microDiamond detector with more advantageous properties 14 , 15 , 28 has been chosen as the reference detector to train the NN. In the second independent test dataset acquired at a different linear accelerator, the deconvolution results have been compared to that measured using a silicon diode due to technical incompatibilities of the microDiamond with equipment from another vendor.…”

Section: Discussionmentioning

confidence: 99%

“…The microDiamond detector was chosen as the reference detector due to its advantageous dosimetric properties. 14 , 15 Contrary to air‐filled chambers, where the density perturbation is causing further beam broadening, the enhanced density of the microDiamond components is causing the opposite effect, i.e., penumbra steepening, and hence compensating largely the VAE. The detector was placed axially such that the detector's axis aligned parallelly to the beam's central axis.…”

Section: Methodsmentioning

confidence: 99%

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Corrections of photon beam profiles of small fields measured with ionization chambers using a three‐layer neural network

Schönfeld

Mund

Yan

et al. 2021

J Applied Clin Med Phys

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The purpose of this work is to study the feasibility of photon beam profile deconvolution using a feedforward neural network (NN) in very small fields (down to 0.56 × 0.56 cm 2 ). The method's independence of the delivery and scanning system is also investigated. Lateral beam profiles of photon fields between 0.56 × 0.56 cm 2 and 4.03 × 4.03 cm 2 were collected on a Siemens Artiste linear accelerator. Three scanning ionization chambers (SNC 125c, PTW 31021, and PTW 31022) of sensitive volumes ranging from 0.016 cm 3 to 0.108 cm 3 were used with a PTW MP3 water phantom. A reference dataset was also collected with a PTW 60019 microDiamond detector to train and test individual NNs for each ionization chamber. Further testing of the trained NNs was performed with additional test data collected on an Elekta Synergy linear accelerator using a Sun Nuclear 3D Scanner. The results were evaluated with a 1D gamma analysis (0.5 mm/0.5%). After the deconvolution, the gamma passing rates increased from 54.79% to 99.58% for the SNC 125c, from 57.09% to 99.83% for the PTW 31021, and from 91.03% to 96.36% for the PTW 31022. The delivery system, the scanning system, the scanning mode (continuous vs. step-by-step), and the electrometer had no significant influence on the results. This study successfully demonstrated the feasibility of using NN to correct the beam profiles of very small photon fields collected with ionization chambers of various sizes. Its independence of the delivery and scanning system was also shown.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Corrections of photon beam profiles of small fields measured with ionization chambers using a three‐layer neural network

Schönfeld

Mund

Yan

et al. 2021

J Applied Clin Med Phys

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“…126,231,232 However, the parallel irradiation of the Gafchromic™ EBT films is discouraged by Fontanarosa et al 233 who observed unacceptable under dosage in PDD at depths greater than 15 cm (about 5% at 20 cm). In general, the detectors that have smallest k f clin, f msr Q clin, Q msr factor (microdiamond, microslicon, plastic scintillator, EBT film) 78,85,97,123,156,158,[186][187][188]192,[234][235][236] are preferred to avoid the need to correct the PDD. If the institution is unable to justify acquisition of at least one of these systems, the method described by Francescon et al 237 and as described in Figure 5 could be adopted.…”

Section: Percentage Depth Dose (Pdd)mentioning

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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“…We also observed experimentally that the response of the 60017-type detector relative to a PTW 31010type Semiflex ionization chamber fell progressively, by up to 2%, at increasing depths in water. 10 This is most likely due to the variation of silicon diode sensitivity with dose-per-linac-pulse observed by Schönfeld et al 11 Recently, PTW-Freiburg commercialized a new "microSilicon" diode detector, the 60023-type. Some materials used in this detector have densities closer to 1 g cm -3 , and the sensitive silicon lattice has been adjusted to minimize the diode's dose-rate dependence.…”

Section: Introductionmentioning

confidence: 99%

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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Technical Note: Characterization of the new microSilicon diode detector

Cited by 22 publications

References 18 publications

Corrections of photon beam profiles of small fields measured with ionization chambers using a three‐layer neural network

Corrections of photon beam profiles of small fields measured with ionization chambers using a three‐layer neural network

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

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

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