Radiation dosimetry of [68Ga]PSMA-11 in low-risk prostate cancer patients

Lin

et al. 2021

Preprint

PurposeThis prospective trial aimed to evaluate the safety, dosimetry, biodistribution, and diagnostic efficacy of a novel theranostic probe 68Ga-DOTA-DiPSMA. Also, we have performed the first comparison with 68Ga-PSMA-11 in prostate cancer (PCa) patients.MethodsFive healthy volunteers and ten PCa patients with a previous clinical 68Ga-PSMA-11 PET/CT were injected with an intravenous bolus of 68Ga-DOTA-DiPSMA with a dose of 1.85MBq/kg. Healthy volunteers received serial whole-body PET scans from the time of injection up to 60 min post-injection, with a second PET/CT scanning at 120 min post-injection. In PCa patients, low-dose CT scan, whole-body PET was performed with 2 min per bed position in 40 min post-injection. In addition, 68Ga-PSMA-11 scanning was performed on PCa patients within 10 days under the same acquisition procedure. Absorbed organ doses and effective doses were calculated using OLINDA/EXM. Normal organ uptake and tumor lesion uptake (SUVmax) were measured. A lesion-by-lesion analysis was performed.Results68Ga-DOTA-DiPSMA administration was safe and well-tolerated. The kidneys received the highest absorbed dose (114.46 ± 29.28 uSv/MBq), followed by the urinary bladder wall (100.82 ± 46.22 uSv/MBq) in accordance with the expected PSMA renal excretion of the tracer. The mean effective dose was 19.46 ± 1.73 μSv/MBq. The SUVmax of 68Ga-PSMA-11 and 68Ga-DOTA-DiPSMA PET/CT for PCa lesions, bone metastases, and lymph node metastases were 11.2 ± 10.76 vs. 4.41 ± 2.72, 7.6 ± 1.58 vs. 2.95 ± 1.11 and 4.86 ± 1.94 vs. 3.26 ± 1.2, respectively.ConclusionInjection of 68Ga-DOTA-DiPSMA is safe and associated with low absorbed and effective doses. Compared to 68Ga-PSMA-11, 68Ga-DOTA-DiPSMA shows comparable pharmacokinetics and detection ability in PCa patients that warrant further head-to-head comparison. Low non-specific uptake in salivary glands and kidneys of 68Ga-DOTA-DiPSMA indicates potential radioligand therapy (RLT) application when labeled with 177Lu, 90Y, or 225Ac.

Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 90%

68Ga-DOTA-DiPSMA PET/CT Imaging: Biodistribution, Dosimetry and First Comparison with 68Ga-PSMA-11 in Prostate Cancer

Lin

et al. 2021

Preprint

Eur J Nucl Med Mol Imaging

“…Secondly, the different tracers used in PET and SPECT imaging (PSMA-11 and PSMA-617, respectively) have similar kinetics; therefore, the kinetics found for PSMA-617 on SPECT can be used to project the expected kinetics of PSMA-11 on PET. Multiple studies investigated biodistribution and kinetics for PSMA-11 [48][49][50][51] and PSMA-617 [52] and showed indeed similar kinetic behavior [53]. Prediction of absorbed dose for lesions showed a large variation in kinetics between patients both during the uptake phase (SD of 50%) and the excretion phase (SD of 30%), indicating that the first assumption of identical lesion kinetics between patients does not hold.…”

Section: Discussionmentioning

confidence: 99%

[68Ga]Ga-PSMA-11 PET imaging as a predictor for absorbed doses in organs at risk and small lesions in [177Lu]Lu-PSMA-617 treatment

Peters

Hofferber

Privé

et al. 2021

Introduction Patient eligibility for [177Lu]Lu-PSMA therapy remains a challenge, with only 40–60% response rate when patient selection is done based on the lesion uptake (SUV) on [68Ga]Ga-PSMA-PET/CT. Prediction of absorbed dose based on this pre-treatment scan could improve patient selection and help to individualize treatment by maximizing the absorbed dose to target lesions while adhering to the threshold doses for the organs at risk (kidneys, salivary glands, and liver). Methods Ten patients with low-volume hormone-sensitive prostate cancer received a pre-therapeutic [68Ga]Ga-PSMA-11 PET/CT, followed by 3 GBq [177Lu]Lu-PSMA-617 therapy. Intra-therapeutically, SPECT/CT was acquired at 1, 24, 48, 72, and 168 h. Absorbed dose in organs and lesions (n = 22) was determined according to the MIRD scheme. Absorbed dose prediction based on [68Ga]Ga-PSMA-PET/CT was performed using tracer uptake at 1 h post-injection and the mean tissue effective half-life on SPECT. Predicted PET/actual SPECT absorbed dose ratios were determined for each target volume. Results PET/SPECT absorbed dose ratio was 1.01 ± 0.21, 1.10 ± 0.15, 1.20 ± 0.34, and 1.11 ± 0.29 for kidneys (using a 2.2 scaling factor), liver, submandibular, and parotid glands, respectively. While a large inter-patient variation in lesion kinetics was observed, PET/SPECT absorbed dose ratio was 1.3 ± 0.7 (range: 0.4–2.7, correlation coefficient r = 0.69, p < 0.01). Conclusion A single time point [68Ga]Ga-PSMA-PET scan can be used to predict the absorbed dose of [177Lu]Lu-PSMA therapy to organs, and (to a limited extent) to lesions. This strategy facilitates in treatment management and could increase the personalization of [177Lu]Lu-PSMA therapy.

Radiation Protection Dosimetry

“…For the nuclear medicine practice, we used the most recent Swiss DRL survey established in 2017 to extract the effective dose coming from radiopharmaceutical products, and we then used various publications for the dose coming from non-referenced radiopharmaceutical products ( 11–13 ) . The median DLP for CT examinations associated with SPECT or PET examinations was extracted from the publication of Lima et al .…”

Section: Methodsmentioning

confidence: 99%

Annual Exposure of the Swiss Population From Medical Imaging in 2018

Viry

Bize

Trueb

et al. 2021

Nationwide surveys on radiation dose to the population from medical imaging are recommended in order to follow trends in population exposure. The goal of the 2018 survey was to investigate the current exposure. The invoice coding information was collected in five university hospitals and large clinics. To improve the estimation of the effective dose delivered in computed tomography (CT), we collected dose data from different Dose Archiving Communication Systems. On average, we found that 1.2 radiological examinations per year and per inhabitant were performed. Dental radiography was the most frequent examination (48% of all the X-ray examinations), followed by conventional radiography (36%) and CT (11%). The average annual effective dose was estimated to be 1.48 mSv per inhabitant, with CT representing 64% of that dose. Our results show that the exposure of the Swiss population from medical imaging has remained stable since 2013, despite a 15% increase in the number of CT examinations.