Small-field radiotherapy photon beam output evaluation: Detectors reviewed

Lam, S.E.; Bradley, D.A.; Khandaker, Mayeen Uddin

doi:10.1016/j.radphyschem.2020.108950

Cited by 20 publications

(17 citation statements)

References 106 publications

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“…In small fields, an additional opposing effect is due to the presence of silicon, which introduces an over-response in small fields due to a fluence perturbation that is not negligible. 146,147 A possible solution is to use the intermediate field method, sometimes referred to as the daisy chain technique [148][149][150] (cross calibration of diode against the chamber in an intermediate field to connect measurements in large fields to small fields) to measure field output factors normalized to a 10 cm 2 × 10 cm 2 field. Although this technique accounts for the energy dependence of large fields, it does not consider the electron fluence perturbation due to the high density of silicon in small fields.…”

Section: Solid-state Detectorsmentioning

confidence: 99%

“… For fields less than 1 cm × 1 cm, the interplay of source occlusion and detector choice demands precise positioning of the detector. The resolution of the scanning measurement should be smallest possible to the limit of device usually 0.1 mm. Dosimetric measurements should be performed with more than one detector system. Strategies to minimize variations in measurements among users should be tested, utilized, and shared The daisy chain approach 148‐150,322 can be used to determine output factors for the complete range of field sizes needed clinically. However, it should be remembered that this method normalizes the response increase in large fields, it does not account for the fluence perturbation effect that may require a correction.…”

Section: Key Recommendations and Summarymentioning

confidence: 99%

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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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Section: Solid-state Detectorsmentioning

confidence: 99%

Section: Key Recommendations and Summarymentioning

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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“…An ideal dosimeter fulfilling all requirements does not currently exist. Commonly used dosimeters in small fields are small volume ionization chambers [10], radiochromic films [11], silicon diodes [12], and diamond detectors [13,14] reports operation principles of solid-state dosimeters and their applications in modern radiation therapy with X-Ray beams while [15] describes the advantages and potential drawbacks of each kind of dosimeter available for small field dosimetry. Pointlike detectors are usually used for small field relative dosimeters, while taking into account variations in space and time of the beam spectrum 1D-2D detectors are desirable [14].…”

Section: Introductionmentioning

confidence: 99%

“…The first studies describing the proprieties of chemical vapor deposition (CVD) and the high-pressure high temperature (HPHT) diamond detectors and their performances as dosimeters are reported in the literature [26,27]. Finally, [14,15] report further developments in diamond detectors and their applications related to small field dosimetry. Compared to the abovementioned papers, this manuscript draws attention to radiotherapy applications of single and poly-crystalline CVD diamond dosimeters, focusing on their performance under photon MegaVoltage beams.…”

Section: Introductionmentioning

confidence: 99%

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

et al. 2021

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Many new X-Ray treatment machines using small and/or non-standard radiation fields, e.g., Tomotherapy, Cyber-knife, and linear accelerators equipped with high-resolution multi-leaf collimators and on-board imaging system, have been introduced in the radiotherapy clinical routine within the last few years. The introduction of these new treatment modalities has led to the development of high conformal radiotherapy treatment techniques like Intensity Modulated photon Radiation Therapy, Volumetric Modulated Arc Therapy, and stereotactic radiotherapy. When using these treatment techniques, patients are exposed to non-uniform radiation fields, high dose gradients, time and space variation of dose rates, and beam energy spectrum. This makes reaching the required degree of accuracy in clinical dosimetry even more demanding. Continuing to use standard field procedures and detectors in fields smaller than 3 × 3 cm2, will generate a reduced accuracy of clinical dosimetry, running the risk to overshadowing the progress made so far in radiotherapy applications. These dosimetric issues represent a new challenge for medical physicists. To choose the most appropriate detector for small field dosimetry, different features must be considered. Short- and long-term stability, linear response to the absorbed dose and dose rate, no energy and angular dependence, are all needed but not sufficient. The two most sought-after attributes for small field dosimetry are water equivalence and small highly sensitive (high sensitivity) volumes. Both these requirements aim at minimizing perturbations of charged particle fluence approaching the Charged Particle Equilibrium condition as much as possible, while maintaining high spatial resolution by reducing the averaging effect for non-uniform radiation fields. A compromise between different features is necessary because no dosimeter currently fulfills all requirements, but diamond properties seem promising and could lead to a marked improvement. Diamonds have long been used as materials for dosimeters, but natural diamonds were only first used for medical applications in the 80 s. The availability of reproducible synthetic diamonds at a lower cost compared to natural ones made the diffusion of diamonds in dosimetry possible. This paper aims to review the use of synthetic poly and single-crystal diamond dosimeters in radiotherapy, focusing on their performance under MegaVoltage photon beams. Both commercial and prototype diamond dosimeters behaviour are described and analyzed. Moreover, this paper will report the main related results in literature, considering diamond development issues like growth modalities, electrical contacts, packaging, readout electronics, and how do they affect all the dosimetric parameters of interest such as signal linearity, energy dependence, dose-rate dependence, reproducibility, rise and decay times.

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“…In SRS procedures, small uncertainties linking to small field profile measurements can result in systematic errors at magnitudes of concern (Lam et al, 2020). The measurement challenges include detector size, positioning issues, and the absence of charged particle equilibrium conditions.…”

Section: Introductionmentioning

confidence: 99%

GeB flat fibre TL dosimeters for in-vivo measurements in radiosurgery

Alyahyawi

Dimitriadis

Nisbet

et al. 2021

Radiation Physics and Chemistry

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Noting an increase in demand for procedures involving clinical radiosurgery we seek to develop a high spatial resolution thermoluminescence dosimeter (TLD) to allow conduct of in vivo dose verification measurements. An associated need is for a dynamic dose range exceeding that of the well-established LiF (Mg,Ti) phosphor TLD-100, with in particular the latter being limited in performance at the elevated doses seen in radiotherapy. The work investigates the performance of a novel GeB co-doped Flat Fibre (GeB-FF) fabricated using the modified chemical vapour deposition (MCVD) process, the hollow capillary optical fibres (COF) produced from this being collapsed down into flat fibres (FF) to create strain-related defects. This process has already been demonstrated to increase the low dose sensitivity of optical fibres, notably at diagnostic x-ray potentials, with Minimum Detectable Dose (MDD) values of down to 0.1 μGy. The intent of present work, conducted as a component of a safety audit, part of the hospital periodic radiation protection quality assurance program, has been to examine and compare the performance of the two forms of TL dosimeter, GeB-FF and TLD-100, measuring scattered radiation resulting from cranial cavity radiosurgery procedures. The dosimeters were placed on the neck, chest and pelvis of 20 patients. Using both types of dosimeter, raw dose values at each site show general accord ( 3 mGy at 1 ), covering mean doses ranging from some 10 mGy to less than 1 mGy, representing doses of < 1% to < 0.1 % of prescribed dose at the treatment site. GeB-FF results uncorrected for energy response show absorbed doses greater than that using TLD-100, by factors of some 1.4, 1.2 and 1.5 for the pelvis, chest and neck respectively; energy corrections have been shown elsewhere to provide for much closer agreement.

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Small-field radiotherapy photon beam output evaluation: Detectors reviewed

Cited by 20 publications

References 106 publications

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

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

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

GeB flat fibre TL dosimeters for in-vivo measurements in radiosurgery

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