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. 2021 Sep:89:1-10.
doi: 10.1016/j.ejmp.2021.07.026. Epub 2021 Jul 30.

Comparison of 90Y SIRT predicted and delivered absorbed doses using a PSF conversion method

Allison J Craig  1 , Iain Murray  2 , Ana M Denis-Bacelar  3 , Bruno Rojas  2 , Jonathan I Gear  2 , Lucy Hossen  4 , Annelies Maenhout  5 , Nasir Khan  5 , Glenn D Flux  2
Affiliations

Comparison of 90Y SIRT predicted and delivered absorbed doses using a PSF conversion method

Allison J Craig et al. Phys Med. 2021 Sep.

Abstract

Purpose: The aims of this study were to develop and apply a method to correct for the differences in partial volume effects of pre-therapy Technetium-99 m (99mTc)-MAA SPECT and post-therapy Yttrium-90 (90Y) bremsstrahlung SPECT imaging in selective internal radiation therapy, and to use this method to improve quantitative comparison of predicted and delivered 90Y absorbed doses.

Methods: The spatial resolution of 99mTc SPECT data was converted to that of 90Y SPECT data using a function calculated from 99mTc and 90Y point spread functions. This resolution conversion method (RCM) was first applied to 99mTc and 90Y SPECT phantom data to validate the method, and then to clinical data to assess the power of 99mTc SPECT imaging to predict the therapeutic absorbed dose.

Results: The maximum difference between absorbed doses to phantom spheres was 178%. This was reduced to 27% after the RCM was applied. The clinical data demonstrated differences within 38% for mean absorbed doses delivered to the normal liver, which were reduced to 20% after application of the RCM. Analysis of clinical data showed that therapeutic absorbed doses delivered to tumours greater than 100 cm3 were predicted to within 52%, although there were differences of up to 210% for smaller tumours, even after the RCM was applied.

Conclusions: The RCM was successfully verified using phantom data. Analysis of the clinical data established that the 99mTc pre-therapy imaging was predictive of the 90Y absorbed dose to the normal liver to within 20%, but had poor predictability for tumours smaller than 100 cm3.

Keywords: Dosimetry; Liver; Microspheres; Radioembolisation; SIRT; Y-90.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
A) example of 99mTc PSF with a Gaussian function fitted to it and B) example of 90Y PSF with the sum of two Gaussian functions fitted to it.
Fig. 2
Fig. 2
Percentage difference of predicted and delivered 90Y absorbed doses to the phantom spheres A) before and B) after application of the RCM. The different shades represent the different sphere-to-background ratios.
Fig. 3
Fig. 3
Histograms of the percentage difference between predicted and delivered mean absorbed dose to the normal liver A) before and B) after application of the RCM. Bin size is 10%.
Fig. 4
Fig. 4
Bland-Altman analysis of predicted versus delivered absorbed doses to normal liver A) before and B) after application of the RCM. The bias shown by the solid line was −17%, reduced to −10% after the application of the RCM. The 95% confidence intervals are represented by the dashed lines.
Fig. 5
Fig. 5
Histograms of the percentage difference between predicted and delivered absorbed dose to the tumours A) before and B) after application of the RCM.
Fig. 6
Fig. 6
Bland-Altman analysis of predicted versus delivered absorbed doses to tumours A) before and B) after application of the RCM. The bias was shown by the solid line as 90%, reduced to 34% after the application of the RCM. The 95% confidence intervals are represented by the dashed lines.
Fig. 7
Fig. 7
Percentage difference between predicted and delivered absorbed doses to the tumours plotted against tumour equivalent diameter A) before and B) after application of the RCM. nce was 271%, and 115% after the RCM was applied.
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