SUV95th as a Reliable Alternative to SUVmax for Determining Renal Uptake in [68Ga] PSMA PET/CT
Widely used in clinical practice, the maximum standardized uptake value (SUVmax) is a statistical index highly prone to physical and biological variations, which can lead to unpredictable errors. This study has a methodological aim: to identify a more robust SUV-based index representing the tracer accumulation. In particular, the new metric was tested to confirm the potential of mannitol to reduce renal uptake Ga-68 prostate-specific membrane antigen ([68Ga]PSMA).
To this aim, our previously published work, proving the efficacy of mannitol, was considered as a background study. Renal SUVmax was calculated in nine patients undergoing [68Ga]PSMA positron emission tomography (PET)/X-ray computed tomography (CT) at baseline (b-PET/CT) and at follow-up after intravenous infusion of 500 ml of 10 % mannitol (m-PET/CT). SUV values of kidney volumes were extracted by a new 3D segmentation method. A new parameter, the median computed on the upper 10% of the SUV distribution (SUV95th), was introduced to better characterize the tracer accumulation. A comparison between SUVmax and SUV95th was also performed. Kruskal-Wallis test was used to assess the statistical significance of the differences in SUV95th between b-PET/CT and m-PET/CT.
SUV95th not only confirmed the efficacy of mannitol as demonstrated in the previous study but improved the separability of b-PET/CT and m-PET/CT examinations, overturning SUVmax findings in two cases. The outcomes of the Kruskal-Wallis test computed for each kidney proved that differences between b-PET/CT and m-PET/CT SUV95th values were significant (p value < 0.001).
Our findings indicate that SUV95th is a more robust index to assess high uptake level, representing a reliable alternative to SUVmax. Independently from the segmentation method, the superiority of SUV95th and its easy computation could make its clinical impact decisive. The results obtained with SUV95th, more representative of tracer uptake than those with SUVmax suggest, in our opinion, that mannitol infusion could be used to reduce the adsorbed dose to the kidneys during [68Ga]PSMA PET/CT and Lu-177 or Ac-225 therapy. Our future goal will be confirming this effect in a larger cohort of patients, also verifying the role of SUV95th in the evaluation of tumor response to therapy.
Key wordsPET/CT SUVmax Reliability Prostate cancer Mannitol PSMA Standardized uptake value Quantitative imaging
The authors would like to thank Filippo Piccinini for his help with data collection during the starting stage of this study.
Study concept and design: AS, AB, SB.
Provision of study materials or patients: FM, AS, EM.
Collection and assembly of data: FM.
Radiopharmaceutical synthesis and quality control: VDI.
Diagnostic imaging: FM, PC.
Analysis and interpretation of data: SB, AB, AS.
Drafting of manuscript: SB.
Critical revision of the manuscript for important intellectual content: GP, AB, FM, AS.
All authors read and approved the final manuscript for submission.
This research was partially supported by the Italian Ministry of Health (grant RF-2016-02364230), and by the Italian Association for Cancer Research (AIRC), (grant IG 20476).
Compliance with Ethical Standards
The protocol was approved by the Ethics Committee of Area Vasta Romagna and by the competent Italian regulatory authorities. The study was performed in accordance with the principles of the Declaration of Helsinki and Good Clinical Practice.
All patients gave their written informed consent.
Conflict of Interest
The authors declare that they have no conflict of interest.
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