A novel statistical analysis method to improve the detection of hepatic foci of (111)In-octreotide in SPECT/CT imaging

Initial Testing of an Approximated, Fast Calculation Procedure for Personalized Dosimetry in Radionuclide Therapy Based on Planar Whole-Body Scan and Monte-Carlo Specific Dose Rates from the OpenDose Project

Individualized dosimetry in nuclear medicine is currently at least advisable in order to obtain the best risk–benefit balance in terms of the maximal dose to lesions and under-threshold doses to radiosensitive organs. This article aims to propose a procedure for fast dosimetric calculations based on planar whole-body scintigraphy (WBS) images and developed to be employed in everyday clinical practice. Methods: For simplicity and legacy reasons, the method is based on planar imaging dosimetry, complemented with some assumptions on the radiopharmaceutical kinetics empirically derived from single-photon emission tomography/computed tomography (SPECT/CT) image analysis. The idea is to exploit a rough estimate of the time-integrated activity as has been suggested for SPECT/CT dosimetry but using planar images. The resulting further reduction in dose estimation accuracy is moderated by the use of a high-precision Monte-Carlo S-factor, such as those available within the OpenDose project. Results: We moved the problem of individualized dosimetry to a transformed space where comparing doses was imparted to the ICRP Average Male/Female computational phantom, resulting from an activity distribution related to patient’s pharmaceutical uptake. This is a fast method for the personalized dosimetric evaluation of radionuclide therapy, bearing in mind that the resulting doses are meaningful in comparison with thresholds calculated in the same framework. Conclusion: The simplified scheme proposed here can help the community, or even the single physician, establish a quantitative guide-for-the-eye approach to individualized dosimetry.

3D printed anthropomorphic left ventricular myocardial phantom for nuclear medicine imaging applications

Background

Anthropomorphic torso phantoms, including a cardiac insert, are frequently used to investigate the imaging performance of SPECT and PET systems. These phantom solutions are generally featuring a simple anatomical representation of the heart. 3D printing technology paves the way to create cardiac phantoms with more complex volume definition. This study aimed to describe how a fillable left ventricular myocardium (LVm) phantom can be manufactured using geometry extracted from a patient image.

Methods

The LVm of a healthy subject was segmented from ¹⁸F-FDG attenuation corrected PET image set. Two types of phantoms were created and 3D printed using polyethylene terephthalate glycol (PETG) material: one representing the original healthy LVm, and the other mimicking myocardium with a perfusion defect. The accuracy of the LVm phantom production was investigated by high-resolution CT scanning of 3 identical replicas. ^99mTc SPECT acquisitions using local cardiac protocol were performed, without additional scattering media (“in air” measurements) for both phantom types. Furthermore, the healthy LVm phantom was inserted in the commercially available DataSpectrum Anthropomorphic Torso Phantom (“in torso” measurement) and measured with hot background and hot liver insert.

Results

Phantoms were easy to fill without any air-bubbles or leakage, were found to be reproducible and fully compatible with the torso phantom. Seventeen segments polar map analysis of the "in air” measurements revealed that a significant deficit in the distribution appeared where it was expected. 59% of polar map segments had less than 5% deviation for the "in torso” and "in air” measurement comparison. Excluding the deficit area, neither comparison had more than a 12.4% deviation. All the three polar maps showed similar apex and apical region values for all configurations.

Conclusions

Fillable anthropomorphic 3D printed phantom of LVm can be produced with high precision and reproducibility. The 3D printed LVm phantoms were found to be suitable for SPECT image quality tests during different imaging scenarios. The flexibility of the 3D printing process presented in this study provides scalable and anthropomorphic image quality phantoms in nuclear cardiology imaging.

Patient dosimetry of 177Lu-PSMA I&T in metastatic prostate cancer treatment: the experience in Thailand

PURPOSE

This study aimed to determine the radiation dosimetry for 177Lu-PSMA imaging and therapy (I&T) in Thai patients who were treated for metastatic prostate cancer.

METHODS

Whole-body planar images acquired at immediately, 4 and 24 h after 177Lu-PSMA I&T injection (range 4.44-8.51 GBq) were collected from 12 treatment cycles of 8 prostate cancer patients. Region of interests (ROIs) were manually contoured on the whole-body, liver, spleen, urinary bladder, lacrimal glands, parotid, and submandibular glands to determine time-integrated activity (TIA) in source organs and fitted time-activity curves using mono-exponential extrapolation. The S values calculated utilizing non-uniform rational B-splines (NURBS) computational phantoms were extracted from the OLINDA/EXM v. 2.0 to calculate the absorbed dose coefficient in target organs according to the Medical Internal Radiation Dose (MIRD) scheme. The absorbed doses to bone marrow were estimated using the planar two-compartment image-based method by separating the high-uptake and low-uptake compartment. The spherical model was used to calculate the lacrimal gland absorbed doses.

RESULTS

Mean absorbed dose coefficients to the kidneys, bone marrow, liver, urinary bladder, spleen, lacrimal glands, parotid, and submandibular glands were 0.81 ± 0.24, 0.02 ± 0.01, 0.13 ± 0.10, 0.27 ± 0.25, 0.16 ± 0.07, 3.62 ± 1.78, 0.21 ± 0.14, and 0.09 ± 0.07 Gy/GBq, respectively. Dose constraints for the kidneys (23 Gy) and bone marrow (2 Gy) were not reached in any patients. The absorbed dose in lacrimal glands calculated by the NURBS computational phantoms was slightly lower than the calculation based on the Cristy-Eckerman computational phantoms using OLINDA/EXM v. 1.0 by 6.37 ± 0.14%.

CONCLUSION

Dosimetry results in this study suggested that 177Lu-PSMA I&T treatment with higher activities and more cycles is possible without the risk of damaging normal organs in prostate cancer patients.

Expanding the PET radioisotope universe utilizing solid targets on small medical cyclotrons

Molecular imaging with medical radioisotopes enables the minimally-invasive monitoring of aberrant biochemical, cellular and tissue-level processes in living subjects. The approach requires the administration of radiotracers composed of radioisotopes attached to bioactive molecules, the pairing of which considers several aspects of the radioisotope in addition to the biological behavior of the targeting molecule to which it is attached. With the advent of modern cellular and biochemical techniques, there has been a virtual explosion in potential disease recognition antigens as well as targeting moieties, which has subsequently opened new applications for a host of emerging radioisotopes with well-matched properties. Additionally, the global radioisotope production landscape has changed rapidly, with reactor-based production and its long-defined, large-scale centralized manufacturing and distribution paradigm shifting to include the manufacture and distribution of many radioisotopes via a worldwide fleet of cyclotrons now in operation. Cyclotron-based radioisotope production has become more prevalent given the commercial availability of instruments, coupled with the introduction of new target hardware, process automation and target manufacturing methods. These advances enable sustained, higher-power irradiation of solid targets that allow hospital-based radiopharmacies to produce a suite of radioisotopes that drive research, clinical trials, and ultimately clinical care. Over the years, several different radioisotopes have been investigated and/or selected for radiolabeling due to favorable decay characteristics (i.e. a suitable half-life, high probability of positron decay, etc.), well-elucidated chemistry, and a feasible production framework. However, longer-lived radioisotopes have surged in popularity given recent regulatory approvals and incorporation of radiopharmaceuticals into patient management within the medical community. This review focuses on the applications, nuclear properties, and production and purification methods for some of the most frequently used/emerging positron-emitting, solid-target-produced radioisotopes that can be manufactured using small-to-medium size cyclotrons (≤24 MeV).

Design study of a brain-dedicated time-of-flight PET system with a hemispherical detector arrangement

Time-of-flight (TOF) is now a standard technology for positron emission tomography (PET), but its effective use for small diameter PET systems has not been studied well. In this paper, we simulated a brain-dedicated TOF-PET system with a hemispherical detector arrangement. We modeled a Hamamatsu TOF-PET module (C13500-4075LC-12) with 280 ps coincidence resolving time (CRT), in which a 12  ×  12 array of multi pixel photon counters (MPPCs) is connected to a lutetium fine silicate (LFS) crystal array of 4.1  ×  4.1 mm² cross section each, based on one-to-one coupling. On the other hand, spatial resolution degradation due to the parallax error should be carefully addressed for the small diameter PET systems. The ideal PET detector would have both depth-of-interaction (DOI) and TOF capabilities, but typical DOI detectors that are based on light sharing tend to degrade TOF performance. Therefore, in this work, we investigated non-DOI detectors with an appropriate crystal length, which was a compromise between suppressed parallax error and decreased sensitivity. Using GEANT4, we compared two TOF detectors, a 20 mm long non-DOI and a 10 mm long non-DOI, with a non-TOF, 4-layer DOI detector with a total length of 20 mm (i.e. 5  ×  4 mm). We simulated a contrast phantom and evaluated the relationship between the contrast recovery coefficient (CRC) and the noise level (the coefficient of variation, COV) for reconstructed images. The 10 mm long non-DOI, which reduces the parallax error at the cost of sensitivity loss, showed better imaging quality than the 20 mm long non-DOI. For example, the CRC value of a 10 mm hot sphere at COV  =  20% was 72% for the 10 mm long non-DOI, which was 1.2 times higher than that of the 20 mm long non-DOI. The converged CRC values for the 10 mm long non-DOI were almost equivalent to those of the non-TOF 4-layer DOI, and the 10 mm long non-DOI converged faster than the non-TOF 4-layer DOI did. Based on the simulation results, we evaluated a one-pair prototype system of the TOF-PET detectors with 10 mm crystal length, which yielded the CRT of 250  ±  8 ps. In summary, we demonstrated support for feasibility of the brain-dedicated TOF-PET system with the hemispherical detector arrangement.

Diagnosis of Alzheimer's Disease Using Dual-Tree Complex Wavelet Transform, PCA, and Feed-Forward Neural Network

Background. Error-free diagnosis of Alzheimer's disease (AD) from healthy control (HC) patients at an early stage of the disease is a major concern, because information about the condition's severity and developmental risks present allows AD sufferer to take precautionary measures before irreversible brain damage occurs. Recently, there has been great interest in computer-aided diagnosis in magnetic resonance image (MRI) classification. However, distinguishing between Alzheimer's brain data and healthy brain data in older adults (age > 60) is challenging because of their highly similar brain patterns and image intensities. Recently, cutting-edge feature extraction technologies have found extensive application in numerous fields, including medical image analysis. Here, we propose a dual-tree complex wavelet transform (DTCWT) for extracting features from an image. The dimensionality of feature vector is reduced by using principal component analysis (PCA). The reduced feature vector is sent to feed-forward neural network (FNN) to distinguish AD and HC from the input MR images. These proposed and implemented pipelines, which demonstrate improvements in classification output when compared to that of recent studies, resulted in high and reproducible accuracy rates of 90.06 ± 0.01% with a sensitivity of 92.00 ± 0.04%, a specificity of 87.78 ± 0.04%, and a precision of 89.6 ± 0.03% with 10-fold cross-validation.

A novel planar image-based method for bone marrow dosimetry in (177)Lu-DOTATATE treatment correlates with haematological toxicity

Background

^177Lu-DOTATATE is a valuable treatment option for patients with advanced neuroendocrine tumours overexpressing somatostatin receptors. Though well tolerated in general, bone marrow toxicity can, besides renal exposure, become dose limiting and affect the ability to sustain future therapies. The aim of this study was to develop a novel planar image-based method for bone marrow dosimetry and evaluate its correlation with haematological toxicity during ¹⁷⁷Lu-DOTATATE treatment. In this study, 46 patients with advanced neuroendocrine tumours were treated with 7.2 GBq (3.5–8.3 GBq) of ¹⁷⁷Lu-DOTATATE on two to five occasions. Planar gamma camera images were acquired at 2, 24, 48 and 168 h post-injection. Whole-body regions of interest were created in the images, and a threshold-based segmentation algorithm was applied to separate the uptake of ¹⁷⁷Lu-DOTATATE into high and low uptake compartments. The conjugate view method was used to quantify the activity, the accumulated activity was calculated and the absorbed dose to the bone marrow was estimated according to the MIRD scheme. Patients were monitored for haematological toxicity based on haemoglobin (Hb), white blood cell (WBC) and platelet (PLT) counts every other week during the treatment period.

Results

The mean absorbed dose to the bone marrow was estimated to 0.20 Gy (0.11–0.37 Gy) per 7.4 GBq of ¹⁷⁷Lu-DOTATATE, and the mean dose per fraction correlated with a decrease in Hb (p = 0.01), WBC (p < 0.01) and PLT (p < 0.01) counts. The total mean absorbed dose to the bone marrow was 0.64 Gy (0.30–1.5 Gy) per 24 GBq (8.2–37 GBq) of ¹⁷⁷Lu-DOTATATE and also correlated with a decrease in Hb (p < 0.01), WBC (p = 0.01) and PLT (p < 0.01) counts.

Conclusions

The planar image-based method developed in this study resulted in similar absorbed doses to the bone marrow as reported in earlier studies with blood-based bone marrow dosimetry. The results correlated with haematological toxicity, making it a promising method for estimating bone marrow doses in ¹⁷⁷Lu-DOTATATE treatment without the need for blood and urine sampling.

Radiation exposure of the spleen during (177)Lu-DOTATATE treatment and its correlation with haematological toxicity and spleen volume

Background

Somatostatin analogue-based radionuclide therapy with ¹⁷⁷Lu-DOTATATE is an important treatment option for patients with advanced neuroendocrine tumours overexpressing somatostatin receptors. In addition to the kidneys, the bone marrow is a major dose-limiting organ. The correlation between developed haematological toxicity and absorbed dose to the bone marrow is poor, which indicates that other factors affect haematological response. The spleen has an important role in the haematopoetic system, including being a reservoir for blood cells. It is also the organ that receives the highest mean absorbed dose during ¹⁷⁷Lu-DOTATATE treatment. The aim of this study was to analyse mean absorbed dose to the spleen and its correlation with haematological toxicity, and to explore changes in splenic volume.

The study included 41 patients treated with 7.2 GBq (3.5–8.3 GBq) of ¹⁷⁷Lu-DOTATATE on two to five occasions. Following each fraction, planar whole-body scans were acquired at 2, 24, 48, and 168 h, and a SPECT/CT at 24 h post-injection. Mean absorbed spleen dose was calculated utilising planar images for time-activity data and SPECT to adjust activity amounts. Splenic volume information was collected from diagnostic CT scans at baseline and follow-up.

Results

Median and total absorbed spleen doses were estimated to 4.5 and 15 Gy, respectively. Total absorbed spleen dose correlated with decrease in Hb (p = 0.02), but not WBC (p = 0.31) or PLT (p = 0.65) counts. For patients without bone metastases, mean absorbed spleen dose correlated with decrease in PLT (p = 0.04) but not Hb (p = 0.16) or WBC (p = 0.42) counts. The spleen volume was reduced to 75 % (p < 0.001) of original values (200 vs. 260 ml) at a mean follow-up of 36 months.

Conclusions

Haematological toxicity according to Hb counts was moderately but significantly correlated with total absorbed spleen dose. This supports the possibility that radiation exposure of the spleen affects overall haematological response during ¹⁷⁷Lu-DOTATATE treatment.