Optimization of Kidney Dosimetry: Determination of Recovery Coefficient for Kidneys and SPECT/CT Imaging of [177Lu]Lu-DOTATATE/TOC
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Date
2025-10-06
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Abstract
Purpose: Peptide receptor radionuclide therapy (PRRT) with [177Lu]Lu-DOTATATE/TOC is
an effective treatment for neuroendocrine tumors, but this treatment also involves an unwanted
radiation dose to the kidneys. Dosimetry can be used to optimize treatment and reduce kidney
toxicity, and therefore, obtaining an accurate estimate of activity concentration in the kidneys
is essential. One of the main challenges in quantitative SPECT imaging for dosimetry is the
partial volume effect, which leads to an underestimation of activity. This effect can be corrected
for by using a recovery coefficient (RC). The study aimed to obtain an RC for kidneys using a
software developed by Hermes for organ and tumor dosimetry. The study investigates how the RC
is affected by different activity concentrations in the kidneys and the ratio between the activity
concentration in the kidney and the background. It was also studied how the RC is affected by
different reconstruction methods and two different projection sets, 30 and 60 projections.
Method: Five 3D-printed kidney phantoms were filled with [177Lu]Lu-DOTATATE/TOC and
placed in either a Jaszczak phantom or a NEMA phantom. Different activity concentrations were
investigated as well as different ratios between the activity concentration in the kidney and the
background. Images were collected with a SPECT/CT system (GE Healthcare Discovery NM/CT
670 Pro) and reconstructed in Hermes (Hermia Hybrid Recon 5.0.) using Ordered Subset Expectation Maximization (OSEM) and Relative Difference Prior (RDP). The kidneys were manually
segmented, and the RC was determined for each measurement. In addition, the RC was compared
between different segmentation methods i.e. the whole kidney segmented volume of interest (VOI),
and the small VOI method was examined.
Results: The RC was not statistically significantly affected by variations in activity concentration or kidney-to-background ratios. However, a statistically significant difference was shown
between the two reconstruction methods, where reconstruction using RDP resulted in a higher RC
than when reconstructing images with OSEM. A statistically significant difference was also found
between 30 and 60 projections, probably due to increased noise in 30 projections. When comparing
various activity concentrations, the whole kidney segmentation approach’s standard deviation was
smaller than that of the small VOIs method. At Sahlgrenska University Hospital, the RC was
determined to be 0.80 with whole kidney segmentation, 60 projections collected and reconstructed
with RDP.
Conclusion: The RC for kidneys in SPECT/CT imaging with [177Lu]Lu-DOTATATE/TOC
are stable across the investigated range of activity concentrations and background ratios, supporting the use of a standardized RC for all imaging time points for whole kidney segmentation in
dosimetry. At Sahlgrenska University Hospital, the RC was determined to be 0.80 and the method
for determination of the RC is considered reasonable.
Description
Syftet: Peptidreceptor-radionuklidterapi (PRRT) med [177Lu]Lu-DOTATATE/TOC ¨ar en effektiv behandling f¨or neuroendokrina tum¨orer, men denna behandling medf¨or ocks˚a en o¨onskad
str˚aldos till njurarna. Dosimetri kan anv¨andas f¨or att optimera behandlingen och minska njurtoxiciteten, och d¨arf¨or ¨ar det avg¨orande att f˚a en noggrann uppskattning av aktivitetskoncentrationen
i njurarna. En av de st¨orsta utmaningarna inom kvantitativ SPECT f¨or dosimetri ¨ar den s˚a kallade
partiella volymseffekten, som leder till en underskattning av aktiviteten. Denna effekt kan korrigeras med hj¨alp av en recovery-koefficient (RC). Syftet med studien var att ta fram en RC f¨or njurar
med hj¨alp av en programvara utvecklad av Hermes f¨or dosimetri av organ och tum¨orer. Studien
unders¨okte hur RC p˚averkas av olika aktivitetskoncentrationer i njurarna samt f¨orh˚allandet mellan aktivitetskoncentrationen i njurarna och i bakgrunden. Det studerades ¨aven hur RC p˚averkas
av olika rekonstruktionsmetoder och tv˚a olika upps¨attningar av projektioner, 30 respektive 60
projektioner.
Metod: Fem 3D-printade njurfantom fylldes med [177Lu]Lu-DOTATATE/TOC och placerades
antingen i ett Jaszczak-fantom eller ett NEMA-fantom. Olika aktivitetskoncentrationer samt olika
f¨orh˚allanden mellan aktivitetskoncentrationen i njurarna och i bakgrunden unders¨oktes. Bilder
samlades in med ett SPECT/CT-system (GE Healthcare Discovery NM/CT 670 Pro) och rekonstruerades i Hermes (Hermia Hybrid Recon 5.0) med hj¨alp av Ordered Subset Expectation Maximization (OSEM) och Relative Difference Prior (RDP). Njurarna segmenterades manuellt och RC
best¨amdes f¨or varje m¨atning. Dessutom j¨amf¨ordes RC mellan olika segmenteringsmetoder, dels
hela njurens segmenterade volym (VOI), dels den s˚a kallade small VOI-metoden.
Resultat: RC p˚averkades inte statistisk signifikant av variationer i aktivitetskoncentration eller
f¨orh˚allandet mellan njure och bakgrund. D¨aremot p˚avisades en statistisk signifikant skillnad mellan
de tv˚a rekonstruktionsmetoderna, d¨ar rekonstruktion med RDP resulterade i en h¨ogre RC j¨amf¨ort
med rekonstruktion med OSEM. En statistisk signifikant skillnad observerades ¨aven mellan 30
och 60 projektioner, troligen p˚a grund av ¨okad brusniv˚a vid 30 projektioner. Vid j¨amf¨orelse
av olika aktivitetskoncentrationer var standardavvikelsen f¨or hela njurens segmentering mindre
¨an f¨or small VOI-metoden. P˚a Sahlgrenska Universitetssjukhuset fastst¨alldes RC till 0,80 med
helnjursegmentering, 60 projektioner insamlade och rekonstruerade med RDP.
Slutsats: RC f¨or njurar vid SPECT/CT-avbildning med [177Lu]Lu-DOTATATE/TOC ¨ar stabil inom det unders¨okta intervallet av aktivitetskoncentrationer och bakgrundsf¨orh˚allanden, vilket
st¨odjer anv¨andningen av en standardiserad RC f¨or samtliga avbildningstillf¨allen vid helnjuresegmentering i dosimetri. Vid Sahlgrenska Universitetssjukhuset fastst¨alldes RC till 0,80 och metoden
f¨or best¨amning av RC anses rimlig.
Keywords
Kidney dosimetry, Segmentation, Recovery coefficient, [177Lu]Lu-DOTATATE, Nuclear Medicin, Activity concentration, OSEM, RDP, Hermes