B. Tan

Post-radioembolization yttrium-90 PET/CT - part 2: dose-response and tumor predictive dosimetry for resin microspheres

BackgroundCoincidence imaging of low-abundance yttrium-90 (90Y) internal pair production by positron emission tomography with integrated computed tomography (PET/CT) achieves high-resolution imaging of post-radioembolization microsphere biodistribution. Part 2 analyzes tumor and non-target tissue dose-response by 90Y PET quantification and evaluates the accuracy of tumor 99mTc macroaggregated albumin (MAA) single-photon emission computed tomography with integrated CT (SPECT/CT) predictive dosimetry.MethodsRetrospective dose quantification of 90Y resin microspheres was performed on the same 23-patient data set in part 1. Phantom studies were performed to assure quantitative accuracy of our time-of-flight lutetium-yttrium-oxyorthosilicate system. Dose-responses were analyzed using 90Y dose-volume histograms (DVHs) by PET voxel dosimetry or mean absorbed doses by Medical Internal Radiation Dose macrodosimetry, correlated to follow-up imaging or clinical findings. Intended tumor mean doses by predictive dosimetry were compared to doses by 90Y PET.ResultsPhantom studies demonstrated near-perfect detector linearity and high tumor quantitative accuracy. For hepatocellular carcinomas, complete responses were generally achieved at D70 > 100 Gy (D70, minimum dose to 70% tumor volume), whereas incomplete responses were generally at D70 < 100 Gy; smaller tumors (<80 cm3) achieved D70 > 100 Gy more easily than larger tumors. There was complete response in a cholangiocarcinoma at D70 90 Gy and partial response in an adrenal gastrointestinal stromal tumor metastasis at D70 53 Gy. In two patients, a mean dose of 18 Gy to the stomach was asymptomatic, 49 Gy caused gastritis, 65 Gy caused ulceration, and 53 Gy caused duodenitis. In one patient, a bilateral kidney mean dose of 9 Gy (V20 8%) did not cause clinically relevant nephrotoxicity. Under near-ideal dosimetric conditions, there was excellent correlation between intended tumor mean doses by predictive dosimetry and those by 90Y PET, with a low median relative error of +3.8% (95% confidence interval, -1.2% to +13.2%).ConclusionsTumor and non-target tissue absorbed dose quantification by 90Y PET is accurate and yields radiobiologically meaningful dose-response information to guide adjuvant or mitigative action. Tumor 99mTc MAA SPECT/CT predictive dosimetry is feasible. 90Y DVHs may guide future techniques in predictive dosimetry.

Use of magnetic resonance imaging in evaluation of placental invasion

AIM To review and describe the magnetic resonance imaging (MRI) features in patients with suspected placental invasion and correlate the findings with surgery and pathology findings. MATERIALS AND METHODS A retrospective review was undertaken of the MRI images of seven consecutive patients with ultrasound findings suspicious for placental invasion. Two experienced MRI radiologists, blinded to the pathology and surgery findings, reviewed the MRI. The pathology or surgical findings were used as the reference standard to establish accuracy and concordance with the MRI findings. RESULTS Three MRI features described in an earlier series were consistently present in the patients with placental invasion: lower uterine bulging, heterogeneous placenta, and dark intraplacental linear bands on T2-weighted images. CONCLUSION MRI features, which were described in patients with placental invasion in an earlier series, were useful in establishing the presence and depth of placental invasion.

Long‐term follow‐up of the treatment of renal angiomyolipomas after selective arterial embolization with alcohol

Study Type – Therapy (case series)
 Level of Evidence 4

Post-radioembolization yttrium-90 PET/CT - part 1: diagnostic reporting

BackgroundYttrium-90 (90Y) positron emission tomography with integrated computed tomography (PET/CT) represents a technological leap from 90Y bremsstrahlung single-photon emission computed tomography with integrated computed tomography (SPECT/CT) by coincidence imaging of low abundance internal pair production. Encouraged by favorable early experiences, we implemented post-radioembolization 90Y PET/CT as an adjunct to 90Y bremsstrahlung SPECT/CT in diagnostic reporting.MethodsThis is a retrospective review of all paired 90Y PET/CT and 90Y bremsstrahlung SPECT/CT scans over a 1-year period. We compared image resolution, ability to confirm technical success, detection of non-target activity, and providing conclusive information about 90Y activity within targeted tumor vascular thrombosis. 90Y resin microspheres were used. 90Y PET/CT was performed on a conventional time-of-flight lutetium-yttrium-oxyorthosilicate scanner with minor modifications to acquisition and reconstruction parameters. Specific findings on 90Y PET/CT were corroborated by 90Y bremsstrahlung SPECT/CT, 99mTc macroaggregated albumin SPECT/CT, follow-up diagnostic imaging or review of clinical records.ResultsDiagnostic reporting recommendations were developed from our collective experience across 44 paired scans. Emphasis on the continuity of care improved overall diagnostic accuracy and reporting confidence of the operator. With proper technique, the presence of background noise did not pose a problem for diagnostic reporting. A counter-intuitive but effective technique of detecting non-target activity is proposed, based on the pattern of activity and its relation to underlying anatomy, instead of its visual intensity. In a sub-analysis of 23 patients with a median follow-up of 5.4 months, 90Y PET/CT consistently outperformed 90Y bremsstrahlung SPECT/CT in all aspects of qualitative analysis, including assessment for non-target activity and tumor vascular thrombosis. Parts of viscera closely adjacent to the liver remain challenging for non-target activity detection, compounded by a tendency for mis-registration.ConclusionsAdherence to proper diagnostic reporting technique and emphasis on continuity of care are vital to the clinical utility of post-radioembolization 90Y PET/CT. 90Y PET/CT is superior to 90Y bremsstrahlung SPECT/CT for the assessment of target and non-target activity.

Metallic endoprostheses for malignant tracheobronchial obstruction: Initial experience

PurposeTo assess the efficacy of the Wallstent endoprosthesis in malignant tracheobronchial obstruction.MethodsSeven patients with irresectable carcinoma of the bronchus were treated with nine Wallstent endoprostheses. The procedures were performed under endoscopic and fluoroscopic guidance. Wallstent endoprostheses ranging from 8–16 mm in diameter and 26–49 mm in length were deployed after balloon dilatation of the strictures.ResultsAll stents were successfully deployed in the desired positions. There was one procedural complication and one procedure-related death. Three patients showed significant improvement in respiratory status after stenting. At a mean follow-up of 5.1 months, there has been no stent migration, fracture, or collapse. One patient had proximal tumor overgrowth that was treated with additional stent insertion. One patient died after a bout of massive hemoptysis 3 months poststenting and it was difficult to tell whether this was related to the endoprosthesis.ConclusionThe use of the Wallstent endoprosthesis in malignant tracheobronchial obstruction is technically feasible.

Dynamic Computed Tomography Angiography: Role in the Evaluation of Popliteal Artery Entrapment Syndrome

This study reviews our experience with dynamic computed tomographic angiography (CTA) as an imaging modality in the evaluation of popliteal artery entrapment syndrome (PAES). Eight patients with surgically proven PAES were included in this study. Dynamic CTA studies performed with the feet in neutral and plantar flexed positions were reviewed for the detailed anatomy of the region and to define the location and extent of the stenosis, occlusions and collateral circulation. These findings were compared with intraoperative observations. CTA provided adequate angiographic and anatomic information required to arrive at the diagnosis and make a surgical decision. Thirteen limbs were affected in eight patients. There was popliteal artery occlusion in four limbs, stenosis at rest that was accentuated on stress imaging in two limbs, and patent popliteal artery with marked stenosis on stress imaging in seven limbs. Long-segment stenosis was seen in functional entrapment compared to short-segment stenosis in anatomic PAES. Anteroposterior compression of the popliteal artery in anatomic PAES unlike the side-to-side compression in functional PAES was a unique observation in this study. The CTA and surgical characterisation and classification of PAES matched in all the patients, except for misinterpretation of compressing fibrous bands as accessory slips of muscles in three limbs. In conclusion, dynamic CTA is a robust diagnostic tool that provides clinically relevant information and serves as a rapidly performed and easily available “one-stop–shop” imaging modality in the management of PAES.

Computed tomography hepatic arteriography has a hepatic falciform artery detection rate that is much higher than that of digital subtraction angiography and 99mTc-MAA SPECT/CT: Implications for planning 90Y radioembolization?

PURPOSE To compare the hepatic falciform artery (HFA) detection rates of digital subtraction angiography (DSA), computed tomography hepatic arteriography (CTHA) and 99mTc-macroaggregated albumin (99mTc-MAA) single photon emission computed tomography with integrated CT (SPECT/CT) and to correlate HFA patency with complication rates of yttrium-90 (90Y) radioembolization. MATERIAL AND METHODS From August 2008 to November 2010, 79 patients (range 23-83 years, mean 62.3 years; 67 male) underwent pre-treatment DSA, CTHA and 99mTc-MAA scintigraphy (planar/SPECT/CT) to assess suitability for radioembolization with 90Y resin microspheres. Thirty-seven patients were excluded from the study, because CTHA was performed with a catheter position that did not result in opacification of the liver parenchyma adjacent to the falciform ligament. DSA, CTHA and 99mTc-MAA SPECT/CT images and medical records were retrospectively reviewed. RESULTS A patent HFA was detected in 22 of 42 patients (52.3%). The HFA detection rates of DSA, CTHA and 99mTc-MAA SPECT/CT were 11.9%, 52.3% and 13.3%, respectively (p<0.0001). An origin from the segment 4 artery was seen in 51.7% of HFAs. Prophylactic HFA coil-embolization prior to 90Y microspheres infusion was performed in 2 patients. Of the patients who underwent radioembolization with a patent HFA, none developed supra-umbilical radiation dermatitis. One patient experienced epigastric pain attributed to post-embolization syndrome and was managed conservatively. CONCLUSION The HFA detection rate of CTHA is superior to that of DSA and 99mTc-MAA SPECT/CT. Complications related to non-target radiation of the HFA vascular territory rarely occur, even in patients undergoing radioembolization with a patent HFA.

Pilot study evaluating catheter-directed contrast-enhanced ultrasound compared to catheter-directed computed tomography arteriography as adjuncts to digital subtraction angiography to guide transarterial chemoembolization

AIM To investigate the feasibility and procedural value of catheter-directed contrast-enhanced ultrasound (CCEUS) compared with catheter-directed computed tomography arteriography (CCTA) in patients undergoing transarterial chemoembolization (TACE) guided by digital subtraction angiography (DSA). MATERIALS AND METHODS From December 2010 to December 2011, a pilot study was conducted including nine patients (mean age 66.6 years; SD 8.3 years; seven men) undergoing TACE with drug-eluting beads for unresectable hepatocellular carcinoma (HCC). Both CCEUS and CCTA were performed in addition to DSA. Alterations of treatment plan based on CCEUS were recorded and compared with CCTA. RESULTS CCEUS provided additional information to DSA altering the treatment plan in four out of nine patients (44.4%). In these four patients, CCEUS helped to identify additional tumour feeders (n = 2) or led to a change in catheter position (n = 2). The information provided by CCEUS was similar to that provided by CCTA. CONCLUSION CCEUS is a potentially valuable imaging tool in adjunction to DSA when performing TACE and may provide similar information to CCTA.

Developing a Radiology Curriculum for a New Medical School in Singapore

Radiology over the past several years has become an increasingly integral component of patient management, not only in helping clinicians coming to a diagnosis through a wide range of imaging modalities, but also in treatment of diseases. Interventional radiology has, in many instances, replaced conventional medical or even surgical therapy as the new standard of care. Despite this increasingly critical role in clinical medicine, there continues to be relatively little emphasis on radiology education in the curriculum of most medical schools. As a result, many interns and residents are not well trained in interpreting simple radiographs and scans or even in requesting the appropriate imaging modality to resolve a particular clinical problem. Despite imaging being such a critical component of day-to-day clinical practice, the lack of clinical radiology training is clearly undesirable and should therefore play a bigger role in medical student education. In 2005, a unique opportunity to develop an innovative teaching program integrating radiology training with core medical education arose when the Singapore Government announced the setting up of a second medical school in Singapore. This new medical school was a partnership between Duke University School of Medicine and the National University of Singapore (NUS), and was to be sited within the campus of Singapore General Hospital (SGH). It was created with the understanding that the majority of the teaching 15

Hemodialysis Access Interventions: An Asian Perspective

The prevalence of end stage renal disease (ESRD) in Singapore is high, and is on an upward trend due to the high incidence of diabetes and an aging population. The crude rates (CR) for ESRD incidence increased from 213.2 per million population (pomp) in 1999 to 295.3 pomp in 2006 [1].