Fetal and maternal absorbed dose estimates for positron-emitting molecular imaging probes

The clinical features, management and outcomes of lymphoma in pregnancy: A multicentre study by the Australasian Lymphoma Alliance

Lymphoma in pregnancy (LIP) presents unique clinical, social and ethical challenges; however, the evidence regarding this clinical scenario is limited. We conducted a multicentre retrospective observational study reporting on the features, management, and outcomes of LIP in patients diagnosed between January 2009 and December 2020 at 16 sites in Australia and New Zealand for the first time. We included diagnoses occurring either during pregnancy or within the first 12 months following delivery. A total of 73 patients were included, 41 diagnosed antenatally (AN cohort) and 32 postnatally (PN cohort). The most common diagnoses were Hodgkin lymphoma (HL; 40 patients), diffuse large B-cell lymphoma (DLBCL; 11) and primary mediastinal B-cell lymphoma (PMBCL; six). At a median follow up of 2.37 years, the 2- and 5-year overall survival (OS) for patients with HL were 91% and 82%. For the combined DLBCL and PMBCL group, the 2-year OS was 92%. Standard curative chemotherapy regimens were successfully delivered to 64% of women in the AN cohort; however, counselling regarding future fertility and termination of pregnancy were suboptimal, and a standardised approach to staging lacking. Neonatal outcomes were generally favourable. We present a large multicentre cohort of LIP reflecting contemporary practice and identify areas in need of ongoing research.

Contrast Agents during Pregnancy: Pros and Cons When Really Needed

Many clinical conditions require radiological diagnostic exams based on the emission of different kinds of energy and the use of contrast agents, such as computerized tomography (CT), positron emission tomography (PET), magnetic resonance (MR), ultrasound (US), and X-ray imaging. Pregnant patients who should be submitted for diagnostic examinations with contrast agents represent a group of patients with whom it is necessary to consider both maternal and fetal effects. Radiological examinations use different types of contrast media, the most used and studied are represented by iodinate contrast agents, gadolinium, fluorodeoxyglucose, gastrographin, bariumsulfate, and nanobubbles used in contrast-enhanced ultrasound (CEUS). The present paper reports the available data about each contrast agent and its effect related to the mother and fetus. This review aims to clarify the clinical practices to follow in cases where a radiodiagnostic examination with a contrast medium is indicated to be performed on a pregnant patient.

Hybrid computational pregnant female phantom construction for radiation dosimetry applications

The number of patients undergoing diagnostic radiology and radiation therapy procedures has increased drastically owing to improvements in cancer diagnosis and treatment and, consequently, patient survival. However, the risk of the occurrence of secondary malignancies due to radiation exposure remains a matter of concern. There are concerns about the fetus's health when pregnant women are exposed to and/or treated with ionizing radiation at various stages of pregnancy. We previously published three hybrid computational fetus phantoms, which contained 27 fetal organs, as a beginning point for developing the whole hybrid computational pregnant phantom set, which is the second objective of this study. An ICRP reference female voxel model was converted to a non-uniform rational basis spline (NURBS) surface model in order to construct a hybrid computational female phantom as a pregnant mother to each fetus model. Both the fetal and maternal organs were matched with ICRP-89 reference data. In order to create a complete standard pregnant computational phantom set at 20, 30, and 35 weeks of pregnancy, the model mother's reproductive organs were removed, and the fetus phantoms with appropriate placental and uterine models were added female pelvis using a 3D-modeling software. With the aid of radiological image sets that had been initially used to construct the fetus models, each fetus' position and rotation inside the uterus were carefully adjusted to represent the real fetal locations inside the uterus. The resulting fetus phantom was positioned in the appropriate location, matching the original radiological image sets. An obstetrician-gynecologist reviewed the complete internal anatomy of all fetus phantoms and the pregnant female for accuracy, and suggested changes were implemented as needed. This new set of hybrid computational pregnant phantom models has realistic anatomical details that can help evaluate fetal radiation doses where realistic fetal computational human phantoms are needed.

Construction of A Digital Fetus Library for Radiation Dosimetry

PURPOSE

Accurate estimation of fetal absorbed dose and radiation risks are crucial for radiation protection and important for radiological imaging research owing to the high radio-sensitivity of the fetus. Computational anthropomorphic models have been widely used in patient-specific radiation dosimetry calculations. In this work, we aim to build the first digital fetal library for more reliable and accurate radiation dosimetry studies.

ACQUISITION AND VALIDATION METHODS

Computed tomography (CT) images of abdominal and pelvic regions of 46 pregnant females were segmented by experienced medical physicists. The segmented tissues/organs include the body contour, skeleton, uterus, liver, kidney, intestine, stomach, lung, bladder, gall bladder, spleen and pancreas for maternal body, and placenta, amniotic fluid, fetal body, fetal brain and fetal skeleton. Non-Uniform Rational B-Spline (NURBS) surfaces of each identified region was constructed manually using 3D modeling software. The Hounsfield unit (HU) values of each identified organs were gathered from CT images of pregnant patients and converted to tissue density. Organ volumes were further adjusted according to reference measurements for the developing fetus recommended by the World Health Organization (WHO) and International Commission on Radiological Protection (ICRP). A series of anatomical parameters, including femur length (FL), humerus length (HL), biparietal diameter (BPD), abdominal circumference (FAC) and head circumference (HC) were measured and compared with WHO recommendations.

DATA FORMAT AND USAGE NOTES

The first fetal patient-specific model library was developed with the anatomical characteristics of each model derived from the corresponding patient whose gestational age varies between 8-weeks and 35-weeks. Voxelized models are represented in the form of MCNP matrix input files representing the three-dimensional model of the fetus. The size distributions of each model are also provided in text files. All data are stored on Zenodo and are publicly accessible on the following link: https://zenodo.org/record/6471884.

POTENTIAL APPLICATIONS

The constructed fetal models and maternal anatomical characteristics are consistent with the corresponding patients. The resulting computational fetus could be used in radiation dosimetry studies to improve the reliability of fetal dosimetry and radiation risks assessment. The advantages of NURBS surfaces in terms of adapting fetal postures and positions enable us to adequately assess their impact on radiation dosimetry calculations. This article is protected by copyright. All rights reserved.

Use of Positron Emission Tomography for Pregnancy-Associated Cancer Assessment: A Review

Background. Positron emission tomography (PET) has proven clinical utility both in the initial and relapse staging phase, but this technique is controversial during pregnancy. The objective of this review is to provide a compendium of available information on the use of PET during pregnancy. Materials and methods. A systematic literature review was conducted from 1 January 2004 until 20 May 2021. A total of 4 small series and 9 case reports consisting of 25 cases were selected. Results. During the first trimester, the fetus is most sensitive to ionization damage, so lower doses are recommended (2.6E-02 mGy/MBq). Fetal-effective doses are higher in this period and the average fetal dose (4.06 ± 3.22 mGy) remains significantly below the threshold for deterministic effects. During the second and third trimesters, recommended doses are higher (1.4E-02 mGy/MBq at 6 months, and 6.9E-03 mGy/MBq at 9 months of gestation). 18F-FDG activity was distributed to the whole fetus with a prevalence of myocardial tissue in seven cases. The use of special precautions, such as PET-magnetic resonance (MR) and urinary bladder catheterization, reduces the amount of radioactive tracer. Breastfeeding interruption is not recommended. Conclusions. 18F-FDG PET is not contraindicated in pregnancy, but multidisciplinary discussion is necessary and strict precautions are recommended.

Feasibility, Safety and Impact of (18F)-FDG PET/CT in patients with pregnancy-associated cancer: experience of the French CALG (Cancer Associé à La Grossesse) network

BACKGROUND

The incidence of pregnancy-associated cancers has been increasing for decades. (18F)-FDG Positron Emission Tomography (PET)/Computed Tomography (CT) imaging has become a golden standard in the staging of many malignant diseases. The aims of the current study were to evaluate the feasibility, safety and impact of (18F)-FDG PET/CT performed during pregnancy.

MATERIAL AND METHODS

A retrospective analysis from the prospective database of the Cancer Associé à La Grossesse (CALG) network (Tenon Hospital, France) including patients who underwent (18F)-FDG PET/CT during their pregnancy between 2015 and 2020.

RESULTS

Of the 536 patients for whom advice from the CALG network was requested during the study period, 359 were diagnosed with cancer during pregnancy. Study population was composed of 63 (17.5%) patients who underwent (18F)-FDG PET/CT. Most cancers were diagnosed during the second trimester. Seventy-five percent were diagnosed with breast cancer, mostly locally advanced invasive ductal carcinomas. Median term of pregnancy at PET/CT was 24.8 weeks of gestation. Twelve (19%), 24 (38.1%) and 22 (34.9%) patients underwent the exam during the 1st, 2nd and 3rd trimester, respectively. (18F)-FDG PET/CT resulted in stage modification for 38 (60.3%) of the patients (28 with more extensive lymph node involvement and 10 with metastatic disease) with subsequently/accordingly modified first-line medical treatment. Fifty patients gave birth to healthy newborns. Two patients had a medical termination of pregnancy, five had a medical abortion, one neonatal death occurred in a patient with severe preeclampsia (unrelated to (18F)-FDG PET/CT). The data of 46 children were available at 6 months, 29 at 12 months, and 15 at 24 months. No cases of mental retardation, childhood cancer, or malformation were reported within 2 years.

CONCLUSION

(18F)-FDG PET/CT has a major impact on the management of pregnancy-associated cancers and does not appear to cause fetal side effects suggesting that the exam is feasible during pregnancy as maternal benefits outweigh fetal risks.

Desmoplastic Small Round Cell Tumor in a Pregnant Woman: A Case Report and Literature Review

Background: Desmoplastic small round cell tumor (DSRCT) is an aggressive malignant tumor commonly found in young men; most occurs in the abdominal cavity. Here we conducted an in-depth analysis of a pregnant patient in our hospital and explored all the case information in the literature on small round cell carcinoma of women. Case presentation: A 27-year-old pregnant woman underwent tumor resection in our hospital at 29 weeks gestational age for a large progressive shoulder lump. The postoperative pathology showed that the mass was a DSRCT. Genetic testing found no fusion gene. At 36 weeks gestation, a painful mass was found in the breast and proved to be a metastatic focus of the desmoplastic small round cell tumor. Twenty days after a successful cesarean section at 40 weeks gestation, she received the VAC-IE chemotherapy regimen, successfully completed the first course, but when awaiting the next chemotherapy, unfortunately, the patient died during follow-up due to tumor recurrence and metastasis. Conclusion: The treatment of DSRCT in pregnant women requires a multidisciplinary consultation, and the treatment and examination during pregnancy are subject to many constraints, which may have a negative impact on the patient's prognosis. Also, a review of the literature found that there is still no standard treatment protocol for DSRCT, and its prognosis in female patients is independent of age and tissue origin.

Qualitative study of nuclear medicine physicians' perceptions of positron emission tomography/computed tomography in pregnant patients with cancer

Staging using positron emission tomography/computed tomography (PET/CT) is standard of care in many cancers that occur most frequently in pregnancy, particularly lymphoma. While expert guidelines generally recommend against PET/CT in pregnant women, there is emerging evidence that likely absorbed foetal doses in pregnancy are relatively low, and as such in certain circumstances PET/CT may be acceptable when balancing benefit and risk. We conducted a qualitative survey of nuclear medicine physicians in Australia and New Zealand to assess practice and attitudes with respect to PET/CT in pregnancy women, finding that most respondents considered PET/CT in pregnancy may be an appropriate modality in carefully selected clinical contexts with appropriate modifications. It is important to continue to define the role of PET/CT in pregnancy into the future, particularly as this imaging modality has emerged as the standard of care in staging and response assessment for many cancers.

Estimation of the radiation dose in pregnancy: an automated patient-specific model using convolutional neural networks

OBJECTIVES

The conceptus dose during diagnostic imaging procedures for pregnant patients raises health concerns owing to the high radiosensitivity of the developing embryo/fetus. The aim of this work is to develop a methodology for automated construction of patient-specific computational phantoms based on actual patient CT images to enable accurate estimation of conceptus dose.

METHODS

We developed a 3D deep convolutional network algorithm for automated segmentation of CT images to build realistic computational phantoms. The neural network architecture consists of analysis and synthesis paths with four resolution levels each, trained on manually labeled CT scans of six identified anatomical structures. Thirty-two CT exams were augmented to 128 datasets and randomly split into 80%/20% for training/testing. The absorbed doses for six segmented organs/tissues from abdominal CT scans were estimated using Monte Carlo calculations. The resulting radiation doses were then compared between the computational models generated using automated segmentation and manual segmentation, serving as reference.

RESULTS

The Dice similarity coefficient for identified internal organs between manual segmentation and automated segmentation results varies from 0.92 to 0.98 while the mean Hausdorff distance for the uterus is 16.1 mm. The mean absorbed dose for the uterus is 2.9 mGy whereas the mean organ dose differences between manual and automated segmentation techniques are 0.07%, - 0.45%, - 1.55%, - 0.48%, - 0.12%, and 0.28% for the kidney, liver, lung, skeleton, uterus, and total body, respectively.

CONCLUSION

The proposed methodology allows automated construction of realistic computational models that can be exploited to estimate patient-specific organ radiation doses from radiological imaging procedures.

KEY POINTS

• The conceptus dose during diagnostic radiology and nuclear medicine imaging procedures for pregnant patients raises health concerns owing to the high radiosensitivity of the developing embryo/fetus. • The proposed methodology allows automated construction of realistic computational models that can be exploited to estimate patient-specific organ radiation doses from radiological imaging procedures. • The dosimetric results can be used for the risk-benefit analysis of radiation hazards to conceptus from diagnostic imaging procedures, thus guiding the decision-making process.

Development of computational pregnant female and fetus models and assessment of radiation dose from positron-emitting tracers

PURPOSE

Molecular imaging using PET and hybrid (PET/CT and PET/MR) modalities nowadays plays a pivotal role in the clinical setting for diagnosis and staging, treatment response monitoring, and radiation therapy treatment planning of a wide range of oncologic malignancies. The developing embryo/fetus presents a high sensitivity to ionizing radiation. Therefore, estimation of the radiation dose delivered to the embryo/fetus and pregnant patients from PET examinations to assess potential radiation risks is highly praised.

METHODS

We constructed eight embryo/fetus models at various gestation periods with 25 identified tissues according to reference data recommended by the ICRP publication 89 representing the anatomy of the developing embryo/fetus. The developed embryo/fetus models were integrated into realistic anthropomorphic computational phantoms of the pregnant female and used for estimating, using Monte Carlo calculations, S-values of common positron-emitting radionuclides, organ absorbed dose, and effective dose of a number of positron-emitting labeled radiotracers.

RESULTS

The absorbed dose is nonuniformly distributed in the fetus. The absorbed dose of the kidney and liver of the 8-week-old fetus are about 47.45 % and 44.76 % higher than the average absorbed dose of the fetal total body for all investigated radiotracers. For ¹⁸F-FDG, the fetal effective doses are 2.90E-02, 3.09E-02, 1.79E-02, 1.59E-02, 1.47E-02, 1.40E-02, 1.37E-02, and 1.27E-02 mSv/MBq at the 8th, 10th, 15th, 20th, 25th, 30th, 35th, and 38th weeks of gestation, respectively.

CONCLUSION

The developed pregnant female/fetus models matching the ICRP reference data can be exploited by dedicated software packages for internal and external dose calculations. The generated S-values will be useful to produce new standardized dose estimates to pregnant patients and embryo/fetus from a variety of positron-emitting labeled radiotracers.

Assessment of radiation dose in nuclear cardiovascular imaging using realistic computational models

PURPOSE

Nuclear cardiology plays an important role in clinical assessment and has enormous impact on the management of a variety of cardiovascular diseases. Pediatric patients at different age groups are exposed to a spectrum of radiation dose levels and associated cancer risks different from those of adults in diagnostic nuclear medicine procedures. Therefore, comprehensive radiation dosimetry evaluations for commonly used myocardial perfusion imaging (MPI) and viability radiotracers in target population (children and adults) at different age groups are highly desired.

METHODS

Using Monte Carlo calculations and biological effects of ionizing radiation VII model, we calculate the S-values for a number of radionuclides (Tl-201, Tc-99m, I-123, C-11, N-13, O-15, F-18, and Rb-82) and estimate the absorbed dose and effective dose for 12 MPI radiotracers in computational models including the newborn, 1-, 5-, 10-, 15-yr-old, and adult male and female computational phantoms.

RESULTS

For most organs, (201)Tl produces the highest absorbed dose whereas (82)Rb and (15)O-water produce the lowest absorbed dose. For the newborn baby and adult patient, the effective dose of (82)Rb is 48% and 77% lower than that of (99m)Tc-tetrofosmin (rest), respectively.

CONCLUSIONS

(82)Rb results in lower effective dose in adults compared to (99m)Tc-labeled tracers. However, this advantage is less apparent in children. The produced dosimetric databases for various radiotracers used in cardiovascular imaging, using new generation of computational models, can be used for risk-benefit assessment of a spectrum of patient population in clinical nuclear cardiology practice.