Predictive accuracy of pre-therapy I-123-NaI dosimetry for patients treated with I-131-NaI as part of the UK multi-centre SELIMETRY trial
Taprogge, J. Yusuf, S. Gear, J. Murray, I. Leek, F. Gregory, R. A. Wevrett, J. Scuffham, J. Tipping, Jill Murby, Brian
Taprogge, J.
Yusuf, S.
Gear, J.
Murray, I.
Leek, F.
Gregory, R. A.
Wevrett, J.
Scuffham, J.
Tipping, Jill
Murby, Brian
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Abstract
Aim/Introduction: The aim of the UK-based multi-centre
clinical trial SELIMETRY (EudraCT No 2015-002269-47) is
to investigate the potential use of the MEK 1/2 inhibitor,
Selumetinib (AZD6244, ARRY-142886), to re-sensitise
patients with iodine refractory differentiated thyroid
cancer to radioiodine therapy. Lesion biokinetic analysis
is performed both for the pre-treatment 123I-NaI and for
the subsequent 131I-NaI therapy. The aim of this study was
to evaluate the potential for the 123I-NaI study to predict
the biokinetics following the therapeutic administration.
Materials and Methods: Pre-treatment dosimetry involved
up to five SPECT/CT scans at 5, 24, 30, 48 and 72 hours
after a 370 MBq 123I-NaI administration following four
weeks of Selumetinib therapy. Four post-therapy SPECT/
CT scans were performed at 24, 48, 72 and 144 hours following radioiodine therapy with 5.5 GBq of 131I-NaI.
rhTSH stimulation was used before 123I-NaI scans and 131I-NaI
therapy. The SPECT scans were quantified using system
calibration factors [1]. Activity retention in lesions was
determined from large VOIs placed on the SPECT scans to
include spill-out due to the partial-volume effect. Activity in
the large VOIs was corrected for background activity. Lesions
were outlined on the CT scans by a trained radiologist to
obtain lesion volumes. Absorbed doses were calculated
using the MIRD formalism. Uncertainties in the absorbed
doses were estimated using recent EANM guidance.
Pearson product-moment correlation coefficients were
computed to assess relationships between results from pretreatment
and post-therapy dosimetry. Results: Preliminary
results obtained for 10 lesions (lesion size range: 0.4 - 42 .3
ml), in 3 patients treated as part of the clinical trial suggest
a strong, positive correlation between predicted activity
retention at 24 hours from the pre-treatment dosimetry
and measured activity retention post-therapy (r=0.98, n=10,
p<0.001). Predicted and measured activity retention at 24
hours after administration agreed in the majority of cases
(8/10) within the associated uncertainties. Furthermore,
a strong, positive correlation between predicted and
measured effective half-lives of activity retention in lesions
assuming a single exponential decay was found (r=0.96,
n=10, p<0.001). Conclusion: Preliminary results suggest that
the lesion biokinetics of pre-treatment 123I-NaI are applicable
to subsequent 131I-NaI therapy of advanced thyroid cancer.
This will potentially allow for a more personalised approach
in the treatment of patients with metastatic thyroid
cancer based on patient-specific dosimetry.
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Date
2020
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Meetings and Proceedings
Citation
Taprogge J, Yusuf S, Gear J, Murray I, Leek F, Gregory RA, et al. Predictive accuracy of pre-therapy I-123-NaI dosimetry for patients treated with I-131-NaI as part of the UK multi-centre SELIMETRY trial. European Journal of Nuclear Medicine and Molecular Imaging. 2020;47(SUPPL 1):S317-S