Influence of patient age on normalized effective doses calculated for CT examinations

Alam, Khursheed; Hillier, Mathew; Shrimpton, Paul; Wall, B. F.

doi:10.1259/bjr.75.898.750819

Cited by 178 publications

(121 citation statements)

References 19 publications

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“…It can be obtained by taking the planar average equilibrium dose and multiplying by the scanning length and a conversion coefficient (“k”) which relates to the organs/tissues under consideration (2) . These conversion coefficients are derived from mathematical phantoms using Monte Carlo modeling (12) . The results obtained were compared with international references 13 , 14 , 15 , 16 …”

Section: Methodsmentioning

confidence: 99%

Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111

Descamps¹,

González²,

Garrigo³

et al. 2012

J Applied Clin Med Phys

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The computed tomography dose index (CTDI) measured with a 10 cm long pencil ionization chamber placed in a 14 cm long PMMA phantom is typically used to evaluate the doses delivered during CT procedure. For the new generation of CT scanners, the efficiency of this methodology is low because it excludes the contribution of radiation scattered beyond the 100 mm range of integration along z. The AAPM TG111 Report proposes a new measurement modality using a small volume ionization chamber positioned in a phantom long enough to establish dose equilibrium at the location of the chamber. In this work, the AAPM report was implemented. The minimum scanning length needed to obtain cumulative dose equilibrium was evaluated. The equilibrium dose was determined and compared to CTDI values informed by the CT scanner, and the dose values were confirmed with TLD measurements. The difference between doses measured with TLD and with the ionization chamber (IC) was below 1% and the repeatability of the measurements' setup was 0.4%. The measurements showed that the scanning lengths needed to reach the cumulated dose equilibrium were 450 mm and 380 mm for the central and peripheral axes, respectively, which justifies the phantom length. For the studied clinical protocols, the doses measured were about 30% higher than those informed by the CT scanner. For the new generation of CT systems with wider longitudinal detector size or cone‐beam technology, the current CTDI measurements may no longer be adequate, and the informed CTDI tends to undervalue the dose delivered. It is therefore important to evaluate CT radiation doses following the AAPM TG111 methodology.PACS number: 87.57.qp, 87.53.Bn

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Section: Methodsmentioning

confidence: 99%

Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111

Descamps¹,

González²,

Garrigo³

et al. 2012

J Applied Clin Med Phys

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show abstract

“…In both methodologies, unlike what happens in the adult, the phantoms are size and age specific [18]. Khursheed et al [19] used the Monte Carlo N-particle (MCNP) radiation transport code to calculate normalised effective dose values for three different scanners and mathematical anthropomorphic phantoms with ages ranging from newborn to adult. They demonstrated the high dependence on patient age and size: the effective dose in a newborn was 1.5 times greater than that of an adult for all types of examinations.…”

Section: Patient Dosementioning

confidence: 99%

CT exposure in adult and paediatric patients: a review of the mechanisms of damage, relative dose and consequent possible risks

et al. 2014

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An increase has been observed not only in the absolute number of CT examinations but also in the length of coverage and number of scanning phases, with the result that exposure to ionising radiation from CT is becoming an increasingly serious problem. The extent of the problem is not entirely known and cannot be adequately addressed without proper knowledge of all the phases that leads to the effective dose calculation. In light of the growing awareness of the issue of ionising radiation dose and the possible risk for the individual and the population, there is a need for radiologists, medical physicists and radiographers to play an active role in dose management. In this review, the authors try to delineate the problem in a consequential and multifaceted way: radiation-patient interaction, possible mechanisms of damage, main CT dose units, risk and its quantification in the population, with the aim of optimising the acquisition dose without diagnostic drawbacks. For an ''up-to-date'' use of CT, radiologists must know the dose concerns for the single patient and population, and use the CT apparatus with the best dose care; substitute CT with other diagnostic techniques when possible, especially in children; reduce the number/extension of scans and phases, and the dose in single scans and single examinations.

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“…The authors noted, however, that the lower estimated dose values compared with other studies ( 62 , 63 ) may be due to the greater than 30% difference in the CTDI value which is used as a normalization factor between measurement and calculation. A number of other studies ( 27 , 31 , 64 ) have also reported Monte Carlo CT dosimetry on pediatric phantoms. However, the results of these studies are reported in terms of normalized effective doses, thus making them difficult to compare with the current study.…”

Section: Discussionmentioning

confidence: 99%

“…Monte Carlo radiation transport simulation has been utilized to estimate organ doses in mathematically stylized phantoms ( 20 – 27 ) or in cylindrical acrylic phantoms. ( 28 – 29 ) These simulations are based upon a rigid and very specific patient geometry and bear little relationship to the real world.…”

Section: Introductionmentioning

confidence: 99%

Patient‐specific CT dosimetry calculation: a feasibility study

Fearon

Xie

Cheng

et al. 2011

J Applied Clin Med Phys

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Current estimation of radiation dose from computed tomography (CT) scans on patients has relied on the measurement of Computed Tomography Dose Index (CTDI) in standard cylindrical phantoms, and calculations based on mathematical representations of “standard man”. Radiation dose to both adult and pediatric patients from a CT scan has been a concern, as noted in recent reports. The purpose of this study was to investigate the feasibility of adapting a radiation treatment planning system (RTPS) to provide patient‐specific CT dosimetry. A radiation treatment planning system was modified to calculate patient‐specific CT dose distributions, which can be represented by dose at specific points within an organ of interest, as well as organ dose‐volumes (after image segmentation) for a GE Light Speed Ultra Plus CT scanner. The RTPS calculation algorithm is based on a semi‐empirical, measured correction‐based algorithm, which has been well established in the radiotherapy community. Digital representations of the physical phantoms (virtual phantom) were acquired with the GE CT scanner in axial mode. Thermoluminescent dosimeter (TLDs) measurements in pediatric anthropomorphic phantoms were utilized to validate the dose at specific points within organs of interest relative to RTPS calculations and Monte Carlo simulations of the same virtual phantoms (digital representation). Congruence of the calculated and measured point doses for the same physical anthropomorphic phantom geometry was used to verify the feasibility of the method. The RTPS algorithm can be extended to calculate the organ dose by calculating a dose distribution point‐by‐point for a designated volume. Electron Gamma Shower (EGSnrc) codes for radiation transport calculations developed by National Research Council of Canada (NRCC) were utilized to perform the Monte Carlo (MC) simulation. In general, the RTPS and MC dose calculations are within 10% of the TLD measurements for the infant and child chest scans. With respect to the dose comparisons for the head, the RTPS dose calculations are slightly higher (10%–20%) than the TLD measurements, while the MC results were within 10% of the TLD measurements. The advantage of the algebraic dose calculation engine of the RTPS is a substantially reduced computation time (minutes vs. days) relative to Monte Carlo calculations, as well as providing patient‐specific dose estimation. It also provides the basis for a more elaborate reporting of dosimetric results, such as patient specific organ dose volumes after image segmentation.PACS numbers: 87.55.D‐, 87.57.Q‐, 87.53.Bn, 87.55.K‐

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Influence of patient age on normalized effective doses calculated for CT examinations

Cited by 178 publications

References 19 publications

Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111

Measurements of the dose delivered during CT exams using AAPM Task Group Report No. 111

CT exposure in adult and paediatric patients: a review of the mechanisms of damage, relative dose and consequent possible risks

Patient‐specific CT dosimetry calculation: a feasibility study

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