A Monte Carlo comparison of the response of the PTW-diamond and the TL-diamond detectors in megavoltage photon beams

Mobit, Paul N; Sandison, George A.

doi:10.1118/1.598771

Cited by 12 publications

(20 citation statements)

References 19 publications

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“…This experimental finding is based on the measure of the sensitivity factors ͑nC/Gy͒ in 6 MV and 25 MV photon beams and in 6 -10-15-22 MeV electron beams. For the photons, this result is confirmed by Mobit et al 2 who, with a Monte Carlo approach, predicted agreement between diamond dosimeter and ionization chamber in the depth dose measurements. Recently, Haryanto et al 3 reported output factors ͑OF͒, percentage depth doses ͑PDD͒ and transverse dose profiles measured with a PTW diamond detector in agreement with Monte Carlo calculations.…”

Section: Introductionsupporting

confidence: 74%

Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size

et al. 2003

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The aim of this work was to test the suitability of a PTW diamond detector for nonreference condition dosimetry in photon beams of different energy (6 and 25 MV) and field size (from 2.6 cm x 2.6 cm to 10 cm x 10 cm). Diamond behavior was compared to that of a Scanditronix p-type silicon diode and a Scanditronix RK ionization chamber. Measurements included output factors (OF). percentage depth doses (PDD) and dose profiles. OFs measured with diamond detector agreed within 1% with those measured with diode and RK chamber. Only at 25 MV, for the smallest field size, RK chamber underestimated OFs due to averaging effects in a pointed shaped beam profile. Agreement was found between PDDs measured with diamond detector and RK chamber for both 6 MV and 25 MV photons and down to 5 cm x 5 cm field size. For the 2.6 cm x 2.6 cm field size, at 25 MV, RK chamber underestimated doses at shallow depth and the difference progressively went to zero in the distal region. PDD curves measured with silicon diode and diamond detector agreed well for the 25 MV beam at all the field sizes. Conversely, the nontissue equivalence of silicon led, for the 6 MV beam, to a slight overestimation of the diode doses in the distal region, at all the field sizes. Penumbra and field width measurements gave values in agreement for all the detectors but with a systematic overestimate by RK measurements. The results obtained confirm that ion chamber is not a suitable detector when high spatial resolution is required. On the other hand, the small differences in the studied parameters, between diamond and silicon systems, do not lead to a significant advantage in the use of diamond detector for routine clinical dosimetry.

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Section: Introductionsupporting

confidence: 74%

Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size

et al. 2003

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“…͑3͒ that accounts for the electron trajectory lengths within the chamber, as that length can be assumed to be proportional to the amount of ionization, and thus to the chamber output. In a recent study, Mobit et al 20 published Monte Carlo data about the direct photon response of a diamond detector. They specify the dose contribution from photon interaction in the cavity material, ␣ c , in terms of percentage, which they calculated in a simulated broad beam.…”

Section: Compton Electron Transportmentioning

confidence: 99%

“…In a recent study, Mobit et al 20 published Monte Carlo data about the direct photon response of a diamond detector. They specify the dose contribution from photon interaction in the cavity material, ␣ c , in terms of percentage, which they calculated in a simulated broad beam.…”

Section: Compton Electron Transportmentioning

confidence: 99%

“…Furthermore, experimental determination of spatial responses is cumbersome and restricted to the specific detector type and beam spectrum used, as the experiments reported in this work underline. Diamond detectors [14][15][16][17][18][19][20] have recently been introduced as high resolu-tion tissue-equivalent detectors, but these detectors are not easily available. Furthermore a distinct photon response of these detectors has recently been reported, 20 similar to photon detector effects reported in diodes.…”

Section: Introductionmentioning

confidence: 99%

“…Diamond detectors [14][15][16][17][18][19][20] have recently been introduced as high resolu-tion tissue-equivalent detectors, but these detectors are not easily available. Furthermore a distinct photon response of these detectors has recently been reported, 20 similar to photon detector effects reported in diodes. 3 In summary, a better knowledge of the spatial response of common dosimeters is definitely needed to obtain a more accurate description of radiotherapy photon beam penumbras.…”

Section: Introductionmentioning

confidence: 99%

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Slit x‐ray beam primary dose profiles determined by analytical transport of Compton recoil electrons

et al. 2000

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Accurate measurement of radiation beam penumbras is essential for conformal radiotherapy. For this purpose a detailed knowledge of the dosimeter's spatial response is required. However, experimental determination of detector spatial response is cumbersome and restricted to the specific detector type and beam spectrum used. A model has therefore been developed to calculate in slit beam geometry both dose profiles and detector response profiles. Summations over representative photon beam spectra yield profiles for polyenergetic beams. In the present study the model is described and resulting dose profiles verified. The model combines Compton scattering of incident photons, transport of resulting electrons by Fermi-Eyges small-angle multiple scattering theory, and functions to limit electron transport. This analytic model thus yields line spread kernels of primary dose in a water phantom. It is shown that the spatial response of an ideal point detector to a primary photon beam can be well described by the model; the calculations are verified by measurements with a diamond detector in a telescopic slit geometry in which all dose contributions except for the primary dose can be excluded. Effects of photon detector behavior, source size of the linear accelerator (linac) and detector size are studied. Measurements show that slit dose profiles calculated by means of the kernel are accurate within 0.1 mm of the full-width at half-maximum. For a theoretical point source and point detector combined with a 0.2 mm wide slit, the full-width half-maximum values of the slit beam dose profiles are calculated as 0.37 mm and 0.42 mm in a 6 MV and 25 MV x-ray beam, respectively. The present study shows that the model is adequate to calculate local dose effects that are dominated by approximately mono-directional, primary photon fluence. The analytic model further provides directional electron fluence information and is designed to be applied to various detectors and linac beam spectra.

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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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A Monte Carlo comparison of the response of the PTW-diamond and the TL-diamond detectors in megavoltage photon beams

Cited by 12 publications

References 19 publications

Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size

Diamond detector versus silicon diode and ion chamber in photon beams of different energy and field size

Slit x‐ray beam primary dose profiles determined by analytical transport of Compton recoil electrons

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

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