SeHCAT retention measurements may be compromised by traces of 177Lu/177mLu more than 90 days after 177Lu-DOTATATE was administered.

[75Se]tauroselcholic acid (SeHCAT) retention measurement provides a noninvasive test for bile acid diarrhea (BAD); however, it is sensitive to the presence of other radionuclides. Two SeHCAT patients at the Royal Free Hospital (RFH) had significant discrepancies between the lower photopeak (111-159 keV) and central photopeak (242-296 keV) windows, indicating contamination with a radionuclide other than 75Selenium. These patients had received lutetium-177 oxodotreotide (177Lu-DOTATATE) therapy 98 and 151 days before their SeHCAT tests. Traces of 177Lu may be retained longer than typically modeled, along with the contaminant 177mLu. This work includes a retrospective audit to examine the prevalence of SeHCAT tests being affected by 177Lu and phantom measurements to investigate the potential impact. Of 579 patients who received 177Lu-DOTATATE therapy at our center, 11 subsequently attended for a SeHCAT test. The two previously identified patients may have had compromised SeHCAT results; however, the other patients had longer intervals between their therapy and test, and their tests are believed to be valid. Spectra were acquired from a phantom containing either a SeHCAT capsule or a mixture of 177Lu/177mLu representative of a patient >90 days after their treatment. The SeHCAT spectrum was scaled to produce simulated day-7 spectra, and the SeHCAT retention that would have been calculated if 177Lu/177mLu were present was determined. All SeHCAT measurement windows are affected by the 177Lu/177mLu, producing clinically significant errors. Patients requiring SeHCAT testing should be asked whether they have ever received 177Lu-DOTATATE. Patient-specific background measurements may be useful for checking for significant levels of other radionuclides.

Dosing lutetium Lu 177-dotatate for a hemodialysis patient.

Lu177-dotatate (Lutathera™) is a radioactive drug approved for the treatment of adults with gastro-entero-pancreatic neuroendocrine tumors and is predominantly renally excreted. Currently all patients receive 7400 MBq (200 mCi), and there are no guidelines for treating hemodialysis patients. We measured radioactivity prior to and post administration of two cycles of Lu177-dotatate in a hemodialysis patient, and radiation exposure to staff. We reduced the standard 7400 MBq by 33% for the first cycle and patient radioactivity fell by 40% following postdilution hemodiafiltration started 6 h post dosing, and by 45% for the second cycle and radioactivity fell by 47% with postdilution hemodiafiltration started 5 h post administration. By reducing the initial administered radioactivity, coupled with early dialysis, and choosing postdilution hemodiafiltration we were able to achieve radioactivity retention curves similar to those from patients with normal renal function receiving the standard administration of 7400 MBq.

Machine learning to predict environmental dose rates from a radionuclide therapy service - a proof of concept study.

The Ionising Radiation Regulations 2017 requires prior risk assessment calculations and regular environmental monitoring of radiation doses. However, the accuracy of prior risk assessments is limited by assumptions and monitoring only provides retrospective evaluation. This is particularly challenging in nuclear medicine for areas surrounding radionuclide therapy patient bathroom wastewater pipework. Machine learning (ML) is a technique that could be applied to patient booking records to predict environmental radiation dose rates in these areas to aid prospective risk assessment calculations, which this proof-of-concept work investigates. 540 days of a dosimeters historical daily average dose rate measurements and the corresponding period of department therapy booking records were used to train six different ML models. Predicted versus measured daily average dose rates for the following 60 days were analysed to assess and compare model performance. A wide range in prediction errors was observed across models. The gradient boosting regressor produced the best accuracy (root mean squared error = 1.10µSv.hr-1, mean absolute error = 0.87µSv.hr-1, mean absolute percentage error = 35% and maximum error = 3.26µSv.hr-1) and goodness of fit (R2= 0.411). Methods to improve model performance and other scenarios where this approach could prove more accurate were identified. This work demonstrates that ML can predict temporal fluctuations in environmental radiation dose rates in the areas surrounding radionuclide therapy wastewater pipework and indicates that it has the potential to play a role in improving legislative compliance, the accuracy of radiation safety and use of staff time and resources.

Uncollimated gamma camera measurements at two metres to the patient provide a practical and statistically robust method for SeHCAT retention calculation.

[75Se]tauroselcholic acid (SeHCAT) retention studies may be performed using a collimated or uncollimated (intrinsic) gamma camera, with trade-offs between counting sensitivity, collision risk, and stray source influence. In this work, we evaluate the uncertainty in SeHCAT studies performed in 'outer room' mode, where the patient sits or stands two metres away from the uncollimated camera face. 768 SeHCAT studies performed at the Royal Free Hospital were analysed retrospectively, and in all cases, the absolute uncertainty was found to be well within the clinically acceptable limit of ±1 percentage point at 15% retention. The mean counting sensitivity was found to be 1.64 cps/kBq, which is higher than collimated counting but lower than uncollimated counting with the patient on the couch. Seeing as the outer room method does not require patients to transfer onto the couch it may provide savings in setup time which may offset the necessarily longer acquisition time. Because the patient does not come into close proximity to the unprotected camera face the risk of collision is also reduced. Spectra from a SeHCAT capsule in a water-filled torso phantom were used to examine the potential impact of modifying the energy windows. We recommend adopting a wide central photopeak and downscatter window (160-296 keV) plus a lower photopeak window (111-159 keV), which may provide significant improvements in sensitivity. This improved sensitivity could be used to reduce the acquisition time, which is of particular interest in the context of increasing numbers of referrals for SeHCAT retention tests.

68Ga-DOTA-TATE PET vs. 123I-MIBG in identifying malignant neural crest tumours.

PURPOSE: We aimed to compare imaging with (123)I-MIBG and (68)Ga-DOTA-TATE in neural crest tumours (NCT) to see if the latter could offer more advantage in detecting extra lesions and have higher sensitivity for malignant lesions. PROCEDURES: We retrospectively reviewed 12 patients (M = 10, F = 2; age range 20-71 years) with NCT (phaeochromocytomas = 7, paragangliomas = 4, medullary thyroid cancer = 1) who underwent both (68)Ga-DOTA-TATE positron emission tomography (PET) or PET/computed tomography (CT) and (123)I-MIBG single-photon emission computed tomography within 6 months. Visual assessment of all lesions and measurement of target/non-target (T/N) ratio in selected lesions were performed. Five patients (aged 50 or less) had SDHB screening results correlated with imaging results of both radiopharmaceuticals. All patients had contrast-enhanced CT and/or other cross-sectional imaging. RESULTS: (68)Ga-DOTA-TATE PET showed tumour lesions in ten out of 12 patients with confirmed disease, while (123)I-MIBG showed lesions in five out of 12 patients. In one patient, both (68)Ga-DOTA-TATE PET and (123)I-MIBG were negative, but CT, magnetic resonance imaging, and 2-deoxy-2-[(18)F]fluoro-D-glucose PET scans identified a lesion in the thorax. (68)Ga-DOTA-TATE and (123)I-MIBG detected a total of 30 lesions, of which 29/30 were positive with (68)Ga-DOTA-TATE and 7/30 with (123)I-MIBG. We also found higher incidence of SDHB positive results in patients with positive (68)Ga-DOTA-TATE. CONCLUSION: Our limited data suggest that (68)Ga-DOTA-TATE is a better imaging agent for NCT and detects significantly more lesions with higher T/N ratio compared to (123)I-MIBG. (68)Ga-DOTA-TATE was more likely to detect malignant lesions as indicated by correlating imaging results with SDHB screening.

Factors affecting the measurement of left ventricular ejection fraction in myocardial perfusion imaging.

BACKGROUND: Estimation of the left ventricular ejection fraction (LVEF) using myocardial perfusion imaging is increasingly used in the evaluation of coronary artery disease. This study aims to compare the effect of (i) two commercially available software packages: quantitative gated single-photon emission computed tomography (SPECT) (QGS) and 4DM-SPECT, and (ii) prereconstruction filtering, on LVEF quantification. METHODS: Images from 101 patients were reconstructed using AutoCardiac and processed using QGS and 4DM-SPECT. Filtering was performed before reconstruction using Hermes FBP SPET on a group of 32 consecutive patients using Butterworth filters (orders 5 and 10; cut-off frequency 0.5-1.2 cycles/cm). RESULTS: Good correlation was observed between QGS and 4DM-SPECT (r=0.88), with an average difference of 2.1%. The difference in LVEF between the two packages ranged from 21 to -28%. The LVEF was overestimated at cut-off frequencies < or = 0.8 cycles/cm compared with higher cut-off frequencies in 26 of 30 (87%) patients. CONCLUSION: There was a clinically significant difference between the LVEF calculated by QGS and 4DM-SPECT and consequently the two packages should not be used interchangeably. The effect of cut-off frequency on LVEF estimation was found to be very patient specific. Changing the cut-off frequency by as little as 0.1 cycles/cm can cause clinically significant differences in LVEF estimation.

Reflections on nurse independent prescribing in the hospital setting.

This article focuses on the experiences of nurses undertaking nurse independent prescribing in the hospital setting. The challenges and benefits are examined using the reflections of those involved in this initiative.