Evaluation of Peak Skin Doses and Lens Doses during Interventional Neuroradiology Using a Direct Measurement System

Objective

In interventional neuroradiology (INR), the evaluation of the peak skin dose (PSD) and lens dose is important because the patient radiation dose increases in cases in which the procedure is more difficult and complex. This study evaluated the radiation doses during INR procedures using a direct measurement system.

Methods

Radiation dose measurements during INR were performed in 332 patients with unruptured aneurysm (URAN), dural arteriovenous fistula (DAVF), and arteriovenous malformation (AVM). The PSD and bilateral lens doses were analyzed for each disease. The Pearson correlation test was used to determine whether the PSD and lens doses were linearly related to the reference air kerma (K_a,r).

Results

In all cases, the PSD and right and left lens doses were 2.36 ± 1.28 Gy, 114.2 ± 54.6 mGy, and 189.8 ± 160.3 mGy, respectively. The PSD and lens doses of the DAVF and AVM cases were significantly higher than those of the URAN case. The Pearson correlation test revealed statistically significant positive correlations between K_a,r and PSD, K_a,r and right lens dose, and K_a,r and left lens dose.

Conclusion

The characteristics of radiation dose in INR were clarified. Owing to the concern of increased radiation doses exceeding the threshold values in DAVF and AVM cases, protection from radiation is required. Simple regression analysis revealed the possibility of precisely predicting PSD using K_a,r.

Technical Note: Relationship between peak skin dose and fluoroscopic Ka,r : Clinical variations and application in establishing substantial radiation dose levels

BACKGROUND

The reference point cumulative air kerma (K_a,r ) is a commonly used dose quantity for establishing substantial radiation dose levels (SRDLs) that can provide guidance for patient dose management actions following fluoroscopically guided procedures. However, the K_a,r may not correlate well with the patient peak skin dose (D_skin,max ) because the relationship between K_a,r and D_skin,max may vary widely due to clinical variations. Therefore, it may be prudent for institutions to establish different K_a,r -based SRDL values based on the clinical procedure type.

PURPOSE

The present study investigates the relationship between K_a,r and D_skin,max for different clinical services and how that variation may overestimate or underestimate the need for patient follow-up. Additionally, the study suggests a possible framework for establishing K_a,r SRDLs based on the clinical data analysis.

METHODS

A retrospective analysis was performed for fluoroscopically guided interventions exceeding 5 Gy K_a,r . For each procedure, the patient D_skin,max was estimated and the ratio of D_skin,max to K_a,r (DKR) was calculated. Results were pooled into one of three clinical service categories: body interventions (n = 33), cardiac interventions (n = 81), or neurological (neuro) interventions (n = 44). The distributions in K_a,r , D_skin,max , and DKR were analyzed in aggregate and by the clinical service category.

RESULTS

The median K_a,r values for procedures exceeding 5 Gy were 6.0 Gy (95% CI [5.6, 6.4]) for body interventions, 5.8 Gy (95% CI [5.5, 6.0]) for cardiac interventions, and 6.3 Gy (95% CI [5.9, 6.6]) for neuro interventions. D_skin,max for the same procedure data sets were 5.0 Gy (95% CI [4.4, 5.6]) for body interventions, 5.5 Gy (95% CI [5.2, 5.8]) for cardiac interventions, and 3.7 Gy (95% CI [3.4, 4.0]) for neuro interventions. This resulted in median DKR values of 0.81 for body interventions, 0.91 for cardiac interventions, and 0.59 for neuro interventions.

CONCLUSIONS

This study illustrates the need to understand the relationship between the reported K_a,r and the patient D_skin,max for different types of interventional procedures. This is especially important when an institution uses K_a,r as the parameter for establishing an SRDL threshold to identify patients who may require clinical follow-up. The implications of this research and a guide for how to implement these findings are elaborated on in the Discussion.

Patient exposure dose in interventional cardiology per clinical and technical complexity levels. Part 1: results of the VERIDIC project

BACKGROUND

Patients can be exposed to high skin doses during complex interventional cardiology (IC) procedures.

PURPOSE

To identify which clinical and technical parameters affect patient exposure and peak skin dose (PSD) and to establish dose reference levels (DRL) per clinical complexity level in IC procedures.

MATERIAL AND METHODS

Validation and Estimation of Radiation skin Dose in Interventional Cardiology (VERIDIC) project analyzed prospectively collected patient data from eight European countries and 12 hospitals where percutaneous coronary intervention (PCI), chronic total occlusion PCI (CTO), and transcatheter aortic valve implantation (TAVI) procedures were performed. A total of 62 clinical complexity parameters and 31 technical parameters were collected, univariate regressions were performed to identify those parameters affecting patient exposure and define DRL accordingly.

RESULTS

Patient exposure as well as clinical and technical parameters were collected for a total of 534 PCI, 219 CTO, and 209 TAVI. For PCI procedures, body mass index (BMI), number of stents ≥2, and total stent length >28 mm were the most prominent clinical parameters, which increased the PSD value. For CTO, these were total stent length >57 mm, BMI, and previous anterograde or retrograde technique that failed in the same session. For TAVI, these were male sex, BMI, and number of diseased vessels. DRL values for Kerma-area product (P_KA), air kerma at patient entrance reference point (K_a,r), fluoroscopy time (FT), and PSD were stratified, respectively, for 14 clinical parameters in PCI, 10 in CTO, and four in TAVI.

CONCLUSION

Prior knowledge of the key factors influencing the PSD will help optimize patient radiation protection in IC.

Part 2: results of the VERIDIC project

BACKGROUND

Optimizing patient exposure in interventional cardiology is key to avoid skin injuries.

PURPOSE

To establish predictive models of peak skin dose (PSD) during percutaneous coronary intervention (PCI), chronic total occlusion percutaneous coronary intervention (CTO), and transcatheter aortic valve implantation (TAVI) procedures.

MATERIAL AND METHODS

A total of 534 PCI, 219 CTO, and 209 TAVI were collected from 12 hospitals in eight European countries. Independent associations between PSD and clinical and technical dose determinants were examined for those procedures using multivariate statistical analysis. A priori and a posteriori predictive models were built using stepwise multiple linear regressions. A fourfold cross-validation was performed, and models' performance was evaluated using the root mean square error (RMSE), mean absolute percentage error (MAPE), coefficient of determination (R²), and linear correlation coefficient (r).

RESULTS

Multivariate analysis proved technical parameters to overweight clinical complexity indices with PSD mainly affected by fluoroscopy time, tube voltage, tube current, distance to detector, and tube angulation for PCI. For CTO, these were body mass index, tube voltage, and fluoroscopy contribution. For TAVI, these parameters were sex, fluoroscopy time, tube voltage, and cine acquisitions. When benchmarking the predictive models, the correlation coefficients were r = 0.45 for the a priori model and r = 0.89 for the a posteriori model for PCI. These were 0.44 and 0.67, respectively, for the CTO a priori and a posteriori models, and 0.58 and 0.74, respectively, for the TAVI a priori and a posteriori models.

CONCLUSION

A priori predictive models can help operators estimate the PSD before performing the intervention while a posteriori models are more accurate estimates and can be useful in the absence of skin dose mapping solutions.

Estimation of patient skin dose in fluoroscopy: summary of a joint report by AAPM TG357 and EFOMP

BACKGROUND

Physicians use fixed C-arm fluoroscopy equipment with many interventional radiological and cardiological procedures. The associated effective dose to a patient is generally considered low risk, as the benefit-risk ratio is almost certainly highly favorable. However, X-ray-induced skin injuries may occur due to high absorbed patient skin doses from complex fluoroscopically guided interventions (FGI). Suitable action levels for patient-specific follow-up could improve the clinical practice. There is a need for a refined metric regarding follow-up of X-ray-induced patient injuries and the knowledge gap regarding skin dose-related patient information from fluoroscopy devices must be filled. The most useful metric to indicate a risk of erythema, epilation or greater skin injury that also includes actionable information is the peak skin dose, that is, the largest dose to a region of skin.

MATERIALS AND METHODS

The report is based on a comprehensive review of best practices and methods to estimate peak skin dose found in the scientific literature and situates the importance of the Digital Imaging and Communication in Medicine (DICOM) standard detailing pertinent information contained in the Radiation Dose Structured Report (RDSR) and DICOM image headers for FGI devices. Furthermore, the expertise of the task group members and consultants have been used to bridge and discuss different methods and associated available DICOM information for peak skin dose estimation.

RESULTS

The report contributes an extensive summary and discussion of the current state of the art in estimating peak skin dose with FGI procedures with regard to methodology and DICOM information. Improvements in skin dose estimation efforts with more refined DICOM information are suggested and discussed.

CONCLUSIONS

The endeavor of skin dose estimation is greatly aided by the continuing efforts of the scientific medical physics community, the numerous technology enhancements, the dose-controlling features provided by the FGI device manufacturers, and the emergence and greater availability of the DICOM RDSR. Refined and new dosimetry systems continue to evolve and form the infrastructure for further improvements in accuracy. Dose-related content and information systems capable of handling big data are emerging for patient dose monitoring and quality assurance tools for large-scale multihospital enterprises.

Validation of a method for estimating peak skin dose from CT-guided procedures

A method for estimating peak skin dose (PSD) from CTDI_vol has been published but not validated. The objective of this study was to validate this method during CT‐guided ablation procedures. Radiochromic film was calibrated and used to measure PSD. Sixty‐eight patients were enrolled in this study, and measured PSD were collected for 46 procedures. CTDI_vol stratified by axial and helical scanning was used to calculate an estimate of PSD using the method [1.2 × CTDI_vol(helical) + 0.6 × CTDI_vol(axial)], and both calculated PSD and total CTDI_vol were compared to measured PSD using paired t‐tests on the log‐transformed data and Bland‐Altman analysis. Calculated PSD were significantly different from measured PSD (P < 0.0001, bias, 18.3%, 95% limits of agreement, −63.0% to 26.4%). Measured PSD were not significantly different from total CTDI_vol (P = 0.27, bias, 3.97%, 95% limits of agreement, −51.6% to 43.7%). Considering that CTDI_vol is reported on the console of all CT scanners, is not stratified by axial and helical scanning modes, and is immediately available to the operator during CT‐guided interventional procedures, it may be reasonable to use the scanner‐reported CTDI_vol as an indicator of PSD during CT‐guided procedures. However, further validation is required for other models of CT scanner.

New real-time patient radiation dosimeter for use in radiofrequency catheter ablation

In a previous study, we reported on a novel (prototype) real-time patient dosimeter with non-toxic phosphor sensors. In this study, we developed new types of sensors that were smaller than in the previous prototype, and clarified the clinical feasibility of our newly proposed dosimeter. Patient dose measurements obtained with the newly proposed real-time dosimeter were compared with measurements obtained using a calibrated radiophotoluminescence glass reference dosimeter (RPLD). The reference dosimeters were set at almost the same positions as the new real-time dosimeter sensors. We found excellent correlations between the reference RPLD measurements and those obtained using our new real-time dosimeter (r2 = 0.967). However, the new type of dosimeter was found to underestimate radiation skin dose measurements when compared with an RPLD. The most probable reason for this was the size reduction in the phosphor sensor of the new type of dosimeter. We believe that, as a result of reducing the phosphor sensor size, the backscattered X-ray irradiation was underestimated. However, the new dosimeter can accurately determine the absorbed dose by correcting the measured value with calibration factors. The calibration factor for the new type dosimeter was determined (by linear regression) to be ~1.15. New real-time patient dosimeter design would be an effective tool for the real-time measurement of patient skin doses during interventional radiology treatments.

A hybrid phantom system for patient skin and organ dosimetry in fluoroscopically guided interventions

PURPOSE

The purpose of this study was to investigate calibrations for improved estimates of skin dose and to develop software for computing absorbed organ doses for fluoroscopically guided interventions (FGIs) with the use of radiation dose structured reports (RDSR) and the UF/NCI family of hybrid computational phantoms.

METHODS AND MATERIALS

Institutional review board approval was obtained for this retrospective study in which ten RDSRs were selected for their high cumulative reference air kerma values. Skin doses were computed using the University of Florida's rapid in-clinic peak skin dose algorithm (or UF-RIPSA). Kerma-area product (KAP) meter calibrations and attenuation of the tabletop with pad were incorporated into the UF-RIPSA. To compute absorbed organ doses the RDSRs were coupled with software to develop Monte Carlo input decks for each irradiation event. The effects of spectrum matching were explored by modeling (a) a polychromatic x-ray energy beam made to match measured first half-value layers of aluminum, (b) an unmatched spectrum, (c) and a mono-energetic beam equivalent to the effective x-ray energy. The authors also considered the practicality of computing organ doses for each irradiation event within a RDSR.

RESULTS

The KAP meter is highly dependent on the quality of the x-ray spectra. Monte Carlo based attenuation coefficients for configurations in which the beam is transmitted through the tabletop with pad reduced the amount by which the software overestimated skin doses. For absorbed organ dose computations, the average ratios of computed organ doses for a non-fitted to fitted spectrum and effective energy to fitted spectrum were 0.45 and 0.03, respectively. Monte Carlo simulations on average took 38 min per patient. All in-field organ tallies converged with a relative error of less than 1% and out-of-field organs tallies within 10% relative error.

CONCLUSIONS

This work details changes to the UF-RIPSA software that include an expanded library of computational phantoms, attenuation coefficients for tabletop with pad, and calibration curves for the KAP meter. For the computation of absorbed organ dose, it is possible to model each irradiation event separately on a patient-dependent model that best morphometrically matches the patient, thus providing a full report of internal organ doses for FGI patients.

Automatic monitoring of localized skin dose with fluoroscopic and interventional procedures

This software tool locates and computes the intensity of radiation skin dose resulting from fluoroscopically guided interventional procedures. It is comprised of multiple modules. Using standardized body specific geometric values, a software module defines a set of male and female patients arbitarily positioned on a fluoroscopy table. Simulated X-ray angiographic (XA) equipment includes XRII and digital detectors with or without bi-plane configurations and left and right facing tables. Skin dose estimates are localized by computing the exposure to each 0.01 × 0.01 m(2) on the surface of a patient irradiated by the X-ray beam. Digital Imaging and Communications in Medicine (DICOM) Structured Report Dose data sent to a modular dosimetry database automatically extracts the 11 XA tags necessary for peak skin dose computation. Skin dose calculation software uses these tags (gantry angles, air kerma at the patient entrance reference point, etc.) and applies appropriate corrections of exposure and beam location based on each irradiation event (fluoroscopy and acquistions). A physicist screen records the initial validation of the accuracy, patient and equipment geometry, DICOM compliance, exposure output calibration, backscatter factor, and table and pad attenuation once per system. A technologist screen specifies patient positioning, patient height and weight, and physician user. Peak skin dose is computed and localized; additionally, fluoroscopy duration and kerma area product values are electronically recorded and sent to the XA database. This approach fully addresses current limitations in meeting accreditation criteria, eliminates the need for paper logs at a XA console, and provides a method where automated ALARA montoring is possible including email and pager alerts.