Improving molecular radiotherapy dosimetry using anthropomorphic calibration

Price, Emlyn; Robinson, Andrew; Cullen, D. M.; Tipping, Jill; Calvert, Nicholas; Hamilton, D.; Oldfield, Christopher J.; Page, Emma; Pietras, Ben; Smith, Andrew

doi:10.1016/j.ejmp.2019.01.013

Cited by 16 publications

(15 citation statements)

References 20 publications

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“…The values for the kidney (0.60 ± 0.01) and spleen inserts (0.61 ± 0.01) agree (within measurement uncertainties) with values reported by [ 25 ] for kidney and spleen inserts corresponding to mathematical models from [ 37 ] for measurements with a GE system. The values for the kidney inserts also agree with the values reported in [ 36 ] for patient-specific inserts based on CT imaging. A similar trend in activity recovery for 177 Lu in kidney phantom inserts corresponding to models from [ 38 ] is reported in [ 24 ] for measurements with a Siemens system.…”

Section: Discussionsupporting

confidence: 88%

“…The data for kidney and spleen obtained without resolution recovery in case of S4 allows a direct comparison with theoretical and experimental activity recovery values reported in previous work [ 24 , 25 , 36 ]. The values for the kidney (0.60 ± 0.01) and spleen inserts (0.61 ± 0.01) agree (within measurement uncertainties) with values reported by [ 25 ] for kidney and spleen inserts corresponding to mathematical models from [ 37 ] for measurements with a GE system.…”

Section: Discussionsupporting

confidence: 52%

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A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project

et al. 2021

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Purpose Patient-specific dosimetry is required to ensure the safety of molecular radiotherapy and to predict response. Dosimetry involves several steps, the first of which is the determination of the activity of the radiopharmaceutical taken up by an organ/lesion over time. As uncertainties propagate along each of the subsequent steps (integration of the time–activity curve, absorbed dose calculation), establishing a reliable activity quantification is essential. The MRTDosimetry project was a European initiative to bring together expertise in metrology and nuclear medicine research, with one main goal of standardizing quantitative 177Lu SPECT/CT imaging based on a calibration protocol developed and tested in a multicentre inter-comparison. This study presents the setup and results of this comparison exercise. Methods The inter-comparison included nine SPECT/CT systems. Each site performed a set of three measurements with the same setup (system, acquisition and reconstruction): (1) Determination of an image calibration for conversion from counts to activity concentration (large cylinder phantom), (2) determination of recovery coefficients for partial volume correction (IEC NEMA PET body phantom with sphere inserts), (3) validation of the established quantitative imaging setup using a 3D printed two-organ phantom (ICRP110-based kidney and spleen). In contrast to previous efforts, traceability of the activity measurement was required for each participant, and all participants were asked to calculate uncertainties for their SPECT-based activities. Results Similar combinations of imaging system and reconstruction lead to similar image calibration factors. The activity ratio results of the anthropomorphic phantom validation demonstrate significant harmonization of quantitative imaging performance between the sites with all sites falling within one standard deviation of the mean values for all inserts. Activity recovery was underestimated for total kidney, spleen, and kidney cortex, while it was overestimated for the medulla. Conclusion This international comparison exercise demonstrates that harmonization of quantitative SPECT/CT is feasible when following very specific instructions of a dedicated calibration protocol, as developed within the MRTDosimetry project. While quantitative imaging performance demonstrates significant harmonization, an over- and underestimation of the activity recovery highlights the limitations of any partial volume correction in the presence of spill-in and spill-out between two adjacent volumes of interests.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionsupporting

confidence: 52%

A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project

et al. 2021

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“…The dashed lines are added to guide the eye and do not indicate a continuity of data. The central Cristy and Eckerman (C&E) spleen data are from Robinson et al [4] and the patient spleen data are from Price et al [5].…”

Section: Resultsmentioning

confidence: 99%

“…The inserts were mounted centrally and then radially displaced in an elliptical Jaszczak phantom apart from the patient spleen in its anatomical position which was mounted in a large elliptical phantom designed to mimic a patient body [5]. Figure 1 shows the positions of the inserts in the phantoms.…”

Section: Methodsmentioning

confidence: 99%

Positional dependence of activity determination in single photon emission computed tomography

Price

Tipping

Cullen

et al. 2019

Nuclear Medicine Communications

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Accurate image quantification requires accurate calibration of the detector and is vital if dosimetry is to be performed in molecular radiotherapy. A dependence on the position of calibration has been observed in single photon emission computed tomography images when attenuation correction (AC) and scatter correction are applied. This work investigates the origin of this dependence in single photon emission computed tomography scans of phantom inserts filled with 177 Lu solution. A 113 ml sphere and inserts representing a mathematical model of a spleen and an anatomical model of a patient spleen were imaged at the centre and edge of elliptical phantoms. For these inserts, the difference in calibration factor between the positions was around 10% for images reconstructed with AC and triple energy window scatter correction. A combination of experimental imaging and Monte Carlo simulation was used to isolate possible causes due to imaging or reconstruction in turn. Inconsistent application of AC between different reconstruction systems was identified as the origin of the positional dependence.

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“…When using global calibration factors, validation measurements or dosimetry audits as required for external beam radiotherapy trials [ 33 ] will become more important. Those measurements range from simple sensitivity measurements to semi- or full-anthropomorphic phantoms [ 34 – 36 ] or testing of the full dosimetry chain [ 24 ]. In the present study, reconstructions are performed locally at the participating centres, which reduces the impact on the central dosimetry hub, but might increase site-dependent biases.…”

Section: Discussionmentioning

confidence: 99%

Setting up a quantitative SPECT imaging network for a European multi-centre dosimetry study of radioiodine treatment for thyroid cancer as part of the MEDIRAD project

et al. 2020

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Background Differentiated thyroid cancer has been treated with radioiodine for almost 80 years, although controversial questions regarding radiation-related risks and the optimisation of treatment regimens remain unresolved. Multi-centre clinical studies are required to ensure recruitment of sufficient patients to achieve the statistical significance required to address these issues. Optimisation and standardisation of data acquisition and processing are necessary to ensure quantitative imaging and patient-specific dosimetry. Material and methods A European network of centres able to perform standardised quantitative imaging of radioiodine therapy of thyroid cancer patients was set-up within the EU consortium MEDIRAD. This network will support a concurrent series of clinical studies to determine accurately absorbed doses for thyroid cancer patients treated with radioiodine. Five SPECT(/CT) systems at four European centres were characterised with respect to their system volume sensitivity, recovery coefficients and dead time. Results System volume sensitivities of the Siemens Intevo systems (crystal thickness 3/8″) ranged from 62.1 to 73.5 cps/MBq. For a GE Discovery 670 (crystal thickness 5/8″) a system volume sensitivity of 92.2 cps/MBq was measured. Recovery coefficients measured on three Siemens Intevo systems show good agreement. For volumes larger than 10 ml, the maximum observed difference between recovery coefficients was found to be ± 0.02. Furthermore, dead-time coefficients measured on two Siemens Intevo systems agreed well with previously published dead-time values. Conclusions Results presented here provide additional support for the proposal to use global calibration parameters for cameras of the same make and model. This could potentially facilitate the extension of the imaging network for further dosimetry-based studies.

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Improving molecular radiotherapy dosimetry using anthropomorphic calibration

Cited by 16 publications

References 20 publications

A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project

A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project

Positional dependence of activity determination in single photon emission computed tomography

Setting up a quantitative SPECT imaging network for a European multi-centre dosimetry study of radioiodine treatment for thyroid cancer as part of the MEDIRAD project

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