Radiation Principles, Protection and Reporting for Interventional Pulmonology.

The use and availability of diverse advanced X-ray based imaging and guidance systems in the field of interventional pulmonology is rapidly growing. This popularity links inextricably to an increase in ionizing radiation use. Knowing ionizing radiation is hazardous, knowledge and competent use of X-ray imaging and guidance systems are important. The globally implemented As Low As Reasonably Achievable (ALARA) principle demands careful attention to minimizing radiation exposure while achieving the precise goals of the intervention and imaging therein. To allow careful and targeted weighing of risk against reward while using X-ray based equipment, proper background knowledge of physics as well as imaging system aspects are needed. This white paper summarizes the principles of ionizing radiation which are crucial to enhance awareness and interpretation of dosimetric quantities. Consecutively, a consensus on standards for reporting radiation exposure in interventional pulmonology procedures is indicated to facilitate comparisons between different systems, approaches and results. Last but not least, it provides a list of practical measures, considerations and tips to optimize procedural imaging as well as reduce radiation dose to patients and staff.

Effective Radiation Dose from Cone-Beam Computed Tomography Guidance during Bronchoscopic Tumour Ablation.

INTRODUCTION: Endobronchial radiofrequency ablation (RFA) is a novel minimally invasive approach to management of peripheral non-small-cell lung cancer (NSCLC) in medically inoperable patients. Minimally invasive ablative techniques are generally delivered with cone-beam computed tomography (CBCT) guidance. CBCT requires a significant number of two dimensional imaging projections to be acquired which is then reconstructed as a three-dimensional cone-beam image. The objective of this study was to determine the radiation dosimetry consequent to use of CBCT guidance for bronchoscopic RFA. METHODS: Post hoc analysis of data following bronchoscopic RFA of stage I biopsy-confirmed NSCLC performed with CBCT. Effective dose estimates for these patients were calculated using PCXMC2.0 software. RESULTS: Ten patients underwent bronchoscopic RFA, with a median 3 (range 2-4) CBCT spins per procedure. Mean dose area product (DAP) per procedure was 7,778 µGy.m2 (±4,743) with an effective dose of 11.6 mSv (±7.4). The DAP per spin for these 10 patients varied from 83.8 to 8,625.6 µGy.m2 (effective dose range 0.15-13.81 mSv). CONCLUSION: This is the first study to report radiation dosimetry consequent to CT guidance for bronchoscopic RFA procedures. Effective doses appear comparable to other CT fluoroscopic procedures.

Diagnostic imaging for suspected pulmonary embolism during pregnancy and postpartum: A comparative radiation dose study.

INTRODUCTION: To compare the radiation dose exposure and diagnostic efficiency of computed tomographic pulmonary angiography (CTPA) and ventilation/perfusion imaging (V/Q) for clinically suspected pulmonary embolism (PE) in pregnant and postpartum women in a tertiary hospital setting. METHODS: A retrospective cohort study of 473 pregnant and postpartum women referred for CTPA or V/Q for clinically suspected PE between January 2013 and December 2018 at a tertiary hospital. Maternal effective radiation dose, breast-absorbed radiation dose and fetal-absorbed dose estimates were calculated. Diagnostic yield was evaluated from radiological findings. RESULTS: Computed tomographic pulmonary angiography (CTPA) was more commonly used for the imaging of suspected PE in pregnant and postpartum populations (51.9% vs. 48.1% and 77.1% vs. 22.9%, respectively). CTPA was associated with higher maternal effective and breast-absorbed doses (maternal effective CTPA 4.7 (±2.9) mSv (millisievert), V/Q 1.7(±0.8) mSv (mean difference 2.93 mSv P < 0.001), and breast-absorbed CTPA 8.0 (±5.2) mGy (milligray), V/Q 0.3 (±0.1) (mean difference 7.67 mGy P < 0.001), respectively). Fetal radiation dose exposure was low. The incidence of positive PE was 5.5%. Indeterminate rates of CTPA and V/Q were 3.0% and 5.5% (P = 0.176), respectively. CONCLUSIONS: Compared to V/Q, CTPA is associated with higher maternal and breast radiation dose; however, modern CT scanners achieve lower radiation doses than historically described. Fetal radiation dose was comparably low. The diagnostic yield of the imaging modalities in pregnant and postpartum women is similar. Revision of guidelines should occur with the advances in CT technology.

CT-Fluoroscopic Guidance for Performance of Targeted Transbronchial Cryobiopsy: A Preliminary Report.

BACKGROUND: Bronchoscopic transbronchial cryobiopsy is increasingly used for the histological assessment of diffuse parenchymal lung disease. Diagnostic performance may be improved by more accurate targeting of biopsy to radiologic abnormalities, and complication rates may be reduced by avoiding biopsy of pleura or larger vessels. OBJECTIVES: To report the preliminary experience of using CT-fluoroscopic guidance for accurate targeting of bronchoscopic transbronchial cryobiopsy. METHODS: Bronchoscopic cryobiopsy was performed in a hybrid CT theatre. 3D CT images were acquired following positioning of the cryoprobe in a distal airway segment. Where cryoprobe position was observed to be too close to the chest wall/diaphragm pleura, or not within the region of interest within the lung parenchyma, re-positioning of probe was undertaken and repeat 3D images were acquired to confirm positioning prior to cryobiopsy. RESULTS: CT-fluoroscopic transbronchial cryobiopsy was successfully performed in 4 patients: 3 patients with interstitial lung infiltrates, and one with an enlarging left upper lobe mass. Images were reviewed following each acquisition to accurately assess the probe position within the lung parenchyma, and relative to other thoracic structures. Intra-procedural imaging was of sufficient quality to allow the accurate positioning of the cryoprobe tip with respect to both the parenchymal region of interest and pleural surfaces. No complications were experienced, and all procedures yielded diagnostic specimens. CONCLUSIONS: Our preliminary experience confirms the feasibility of performing transbronchial cryobiopsy under CT-fluoroscopic guidance. Accurate targeting of transbronchial cryobiopsy may be achieved using CT-fluoroscopic guidance. Positioning of the probe tip, both with respect to parenchymal region of interest and to pleural surfaces, can be established with high accuracy.

Ultralow dose CT for follow-up of solid pulmonary nodules: A pilot single-center study using Bland-Altman analysis.

Solid pulmonary nodules are a common finding requiring serial computed tomography (CT) imaging. We sought to explore the detection and measurement accuracy of an ultralow-dose CT (ULDCT) protocol compared with our standard low-dose CT (LDCT) nodule follow-up protocol.In this pragmatic single-center pilot prospective cohort study, patients scheduled for clinically indicated CT surveillance of 1 or more known solid pulmonary nodules >2 mm underwent ULDCT immediately after routine LDCT. The Bland-Altman 95% limits of agreement for diameter and volumetry were calculated.In all, 57 patients underwent 60 imaging episodes, with 170 evaluable nodules. ULDCT detected all known solid pulmonary nodules >2 mm. Bland-Altman analyses demonstrated clinically agreement for both nodule diameter and volume, both of which fell within prespecified limits.This single-center pilot study suggests that ULDCT may be of use in surveillance of known solid pulmonary nodules >2 mm.

Dynamic CT for Parathyroid Adenoma Detection: How Does Radiation Dose Compare With Nuclear Medicine?

OBJECTIVE: Dynamic CT is increasingly used for preoperative localization of parathyroid adenomas, but concerns remain about the radiation effective dose of CT compared with that of 99mTc-sestamibi scintigraphy. The purpose of this study was to compare the radiation dose delivered by three-phase dynamic CT with that delivered by 99mTc-sestamibi SPECT/CT performed in accordance with our current protocols and to assess the possible reduction in effective dose achieved by decreasing the scan length (i.e., z-axis) of two phases of the dynamic CT protocol. MATERIALS AND METHODS: The effective dose of a 99mTc-sestamibi nuclear medicine parathyroid study performed with and without coregistration CT was calculated and compared with the effective dose of our current three-phase dynamic CT protocol as well as a proposed protocol involving CT with reduced scan length. RESULTS: The median effective dose for a 99mTc-sestamibi nuclear medicine study was 5.6 mSv. This increased to 12.4 mSv with the addition of coregistration CT, which is higher than the median effective dose of 9.3 mSv associated with the dynamic CT protocol. Reducing the scan length of two phases in the dynamic CT protocol could reduce the median effective dose to 6.1 mSv, which would be similar to that of the dose from the 99mTc-sestamibi study alone. CONCLUSION: Dynamic CT used for the detection of parathyroid adenoma can deliver a lower radiation dose than 99mTc-sestamibi SPECT/CT. It may be possible to reduce the dose further by decreasing the scan length of two of the phases, although whether this has an impact on accuracy of the localization needs further investigation.

Four-Dimensional Computed Tomography: Clinical Impact for Patients with Primary Hyperparathyroidism.

BACKGROUND: In recent years, four-dimensional computed tomography (4DCT) has emerged as a new localization study for primary hyperparathyroidism (pHPT). OBJECTIVE: We aimed to assess the added value of 4DCT in our institution in the first 4 years of use. METHODS: A retrospective cohort study was conducted from February 2004 to June 2015. Since 2011, patients over 50 years of age without concordant sestamibi-SPECT (SeS) and ultrasound (US) findings underwent 4DCT. Imaging results, surgical findings, histopathology, and postoperative biochemistry were collected. RESULTS: A total of 536 parathyroid operations in 510 patients were performed during the study period. The overall cure rate was 99.2% after reoperation in some patients, and the overall sensitivity for SeS was 76.0%, and 74.8% for US. Since 2011, 100 patients without concordant SeS/US findings have undergone 4DCT, with a sensitivity of 72.9%. This is in comparison to the sensitivities for SeS (48.3%) and US (52.3%). 4DCT was more sensitive in patients with persistent/recurrent disease (60.0% compared with SeS 43.8% and US 36.4%) and patients with multigland disease (67.4% compared with SeS 40.9% and US 42.1%). Comparison between outcomes in the pre- versus post-CT era demonstrated no difference in the initial cure rate (95.4 vs. 95.9%, p = 0.85) or the rate of minimally invasive parathyroidectomies (74.5 vs. 79.9%, p = 0.22). CONCLUSION: Parathyroid 4DCT can aid surgical planning in cases without concordant SeS/US findings; however, the introduction of 4DCT as a second-line test did not change our overall cure rate or rate of minimally invasive parathyroidectomy. The role of 4DCT as the primary localization study for pHPT merits further investigation.

CT brain perfusion: A static phantom study of contrast-to-noise ratio and radiation dose.

INTRODUCTION: Computed tomography perfusion (CTP) is increasingly employed in the diagnosis and management of ischaemic stroke but radiation dose can be significant and optimising contrast-to-noise ratio (CNR) is challenging. This study aimed to quantify and optimise the balance between CNR as a surrogate for image quality and radiation dose. METHODS: A perspex head phantom with vials of dilute contrast agent was scanned using a Siemens Definition Flash 128-slice scanner. The CTP protocol exposure parameters were adjusted over 70-120 kVp and 150-285 mAs. Measurements were obtained for the average dose per slice, Hounsfield Units (HU) for iodinated contrast agent, and the image noise for background regions of perspex. The CNR was measured as a function of the volumetric CT dose index (CTDIvol) and kVp. RESULTS: A change from 120 to 80 kVp, achieved the same CNR with 60% reduction in dose. Alternatively, for the same dose, the change from 120 to 80 kVp improved CNR by +58%. A change from 80 to 70 kVp while operating at the same CNR, led to 13% reduction in dose. Alternatively, maintaining the same dose while changing from 80 to 70 kVp improved the CNR by +7%. CONCLUSION: Lower beam energies achieved the same CNR with less dose, or improved CNR at the same dose. A reduction from 80 kVp to 70 kVp may be clinically useful to optimise CTP acquisitions.

Justifying the use of abdominal wall computed tomographic angiography in deep inferior epigastric artery perforator flap planning.

Abdominal wall computed tomography angiography (CTA) is used to guide preoperative planning and intraoperative technique for deep inferior epigastric artery perforator free flap breast reconstructive surgery. This study considers the amount of radiation delivered to the patient, outlining how scan parameters can be optimized to minimize the radiation exposure whilst maintaining image quality. Results of scan parameters and dose reports for 34 patients undergoing abdominal wall CTA are compared with those patients undergoing routine abdominal computed tomography. The links between computed tomography dose quantities are explained, including their conversion to effective dose (in mSv) and risk as the probability for inducing deterministic effects (eg, skin burns) and stochastic effects (ie, cancer induction). The mean effective dose by using our technique for routine abdominal computed tomography is 9.9 and for abdominal wall CTA is 6.0 mSv. All doses are far below the thresholds for deterministic effects to the skin. Abdominal wall CTA can be justified before major reconstructive surgery if the surgeon believes that the very low estimated risk of fatal radiation-induced cancer (1 in 4270 for 6 mSv) is outweighed by the benefits.

Radiation dose to patients and clinicians during fluoroscopically-guided biopsy of peripheral pulmonary lesions.

BACKGROUND: Fluoroscopic guidance may be utilized in some bronchoscopic procedures, including ultrasound-guided bronchoscopy for investigation of peripheral pulmonary lesions. Some authors have suggested this procedure may be performed without fluoroscopy, to minimize risks due to radiation exposure. However, the radiation dose has never been quantified, so the risk remains unknown. OBJECTIVE: To determine the patient and clinician radiation exposure from fluoroscopy during bronchoscopy. METHODS: We recorded exposure parameters during 45 consecutive ultrasound bronchoscopies with fluoroscopic guidance with a mobile C-arm fluoroscopy system. We calculated the patient effective radiation dose with Monte Carlo computer simulations. Passive personal film dosimeters were placed on 4 sites on both the proceduralist and the primary nursing assistant. RESULTS: The mean fluoroscopy screening time was 96 ± 55 s. Patients received a median effective radiation dose of 0.49 ± 0.37 milli-Sieverts (mSv) (range 0.16-1.3 mSv). Only the film dosimeters worn outside the clinicians' protective aprons recorded measurable radiation doses. Based on typical attenuation properties of the protective garments across the diagnostic x-ray energy range, we estimate that the effective radiation dose per procedure to the proceduralist was 0.4 micro-Sieverts (µSv) and to the assistant was 0.2 µSv. CONCLUSIONS: Patients are exposed to relatively small amounts of radiation from fluoroscopy during bronchoscopy. Clinically indicated fluoroscopic guidance during bronchoscopy should not be precluded on the basis of radiation safety concerns. Adequate shielding of clinicians results in negligible radiation doses during ultrasound bronchoscopy.