Patient Skin Dose Research Articles

SU‐D‐209‐04: Raise Your Table: An Effective Way to Reduce Radiation Dose for Fluoroscopy

Purpose:Patient table height plays an important role in estimating patient skin dose for interventional radiology (IR) procedures, because the patient's skin location is dependent on the height of table. Variation in table height can lead to as much as 150% difference in skin dose for patient exams with similar air kerma meter readings. In our facility, IR procedural workflow was recently changed to require the IR physicians to confirm the patient table height before the procedure. The patient table height data was collected before and after this workflow change to validate the implementation of this practice.Methods:Table height information was analyzed for all procedures performed in three IR rooms, which were impacted by the workflow change, covering three months before and after the change (Aug 2015 to Jan 2016). In total, 442, 425, and 390 procedures were performed in these three rooms over this time period. There were no personnel or procedure assignment changes during the six‐month period of time. Statistical analysis was performed for the average table height changes before and after the workflow change.Results:For the three IR rooms investigated, after the workflow change, the average table heights were increased by 1.43 cm (p=0.004084), 0.66 cm (p=0.187089), and 1.59 cm (p=0.002193), providing a corresponding estimated skin dose savings of 6.76%, 2.94% and 7.62%, respectively. After the workflow change, the average table height was increased by 0.95 cm, 0.63 cm, 0.55 cm, 1.07 cm, 1.12 cm, and 3.36 cm for the six physicians who routinely work in these three rooms.Conclusion:Consistent improvement in table height settings has been observed for all IR rooms and all physicians following a simple workflow change. This change has led to significant patient dose savings by making physicians aware of the pre‐procedure table position.

TCT-281 Real-Time Radiation Monitoring Reduces Patient Peak Skin Dose During Coronary Angiography

Exposure to ionizing radiation during coronary angiography can have dose related effects including skin damage. Angiography systems providing a real-time pictorial display of patient skin dose are now available. Hypothesis: The use of a real-time radiation skin dose monitor displaying a color

Percutaneous Renal Tumor Ablation: Radiation Exposure During Cryoablation and Radiofrequency Ablation.

Once reserved solely for non-surgical cases, percutaneous ablation is becoming an increasingly popular treatment option for a wider array of patients with small renal masses and the radiation risk needs to be better defined as this transition continues. Retrospective review of our renal tumor ablation database revealed 425 patients who underwent percutaneous ablation for treatment of 455 renal tumors over a 5-year time period. Imparted radiation dose information was reviewed for each procedure and converted to effective patient dose and skin dose using established techniques. Statistical analysis was performed with each ablative technique. For the 331 cryoablation procedures, the mean DLP was 6987mGycm (SD=2861) resulting in a mean effective dose of 104.7mSv (SD=43.5) and the mean CTDIvol was 558mGy (SD=439) resulting in a mean skin dose of 563.2mGy (SD=344.1). For the 124 RFA procedures, the mean DLP was 3485mGycm (SD=1630) resulting in a mean effective dose of 50.3mSv (SD=24.0) and the mean CTDIvol was 232mGy (SD=149) resulting in a mean skin dose of 233.2mGy (SD=117.4). The difference in patient radiation exposure between the two renal ablation techniques was statistically significant (p<0.001). Both cryoablation and RFA imparted an average skin dose that was well below the 2Gy deterministic threshold for appreciable sequela. Renal tumor cryoablation resulted in a mean skin and effective radiation dose more than twice that for RFA. The radiation exposure for both renal tumor ablation techniques was at the high end of the medical imaging radiation dose spectrum.

Characterization of XR-RV3 GafChromic(®) films in standard laboratory and in clinical conditions and means to evaluate uncertainties and reduce errors.

To investigate the optimal use of XR-RV3 GafChromic(®) films to assess patient skin dose in interventional radiology while addressing the means to reduce uncertainties in dose assessment. XR-Type R GafChromic films have been shown to represent the most efficient and suitable solution to determine patient skin dose in interventional procedures. As film dosimetry can be associated with high uncertainty, this paper presents the EURADOS WG 12 initiative to carry out a comprehensive study of film characteristics with a multisite approach. The considered sources of uncertainties include scanner, film, and fitting-related errors. The work focused on studying film behavior with clinical high-dose-rate pulsed beams (previously unavailable in the literature) together with reference standard laboratory beams. First, the performance analysis of six different scanner models has shown that scan uniformity perpendicular to the lamp motion axis and that long term stability are the main sources of scanner-related uncertainties. These could induce errors of up to 7% on the film readings unless regularly checked and corrected. Typically, scan uniformity correction matrices and reading normalization to the scanner-specific and daily background reading should be done. In addition, the analysis on multiple film batches has shown that XR-RV3 films have generally good uniformity within one batch (<1.5%), require 24 h to stabilize after the irradiation and their response is roughly independent of dose rate (<5%). However, XR-RV3 films showed large variations (up to 15%) with radiation quality both in standard laboratory and in clinical conditions. As such, and prior to conducting patient skin dose measurements, it is mandatory to choose the appropriate calibration beam quality depending on the characteristics of the x-ray systems that will be used clinically. In addition, yellow side film irradiations should be preferentially used since they showed a lower dependence on beam parameters compared to white side film irradiations. Finally, among the six different fit equations tested in this work, typically used third order polynomials and more rational and simplistic equations, of the form dose inversely proportional to pixel value, were both found to provide satisfactory results. Fitting-related uncertainty was clearly identified as a major contributor to the overall film dosimetry uncertainty with up to 40% error on the dose estimate. The overall uncertainty associated with the use of XR-RV3 films to determine skin dose in the interventional environment can realistically be estimated to be around 20% (k = 1). This uncertainty can be reduced to within 5% if carefully monitoring scanner, film, and fitting-related errors or it can easily increase to over 40% if minimal care is not taken. This work demonstrates the importance of appropriate calibration, reading, fitting, and other film-related and scan-related processes, which will help improve the accuracy of skin dose measurements in interventional procedures.

TH-AB-201-01: A Real-Time Skin-Dose Mapping System for Region-Of-Interest (ROI) Fluoroscopy

Purpose: The real-time dose-tracking system (DTS) which we developed for fluoroscopically–guided procedures has been upgraded so that it can track the patient skin dose when using a region-of-interest (ROI) beam attenuator. Methods: ROI fluoroscopy is a method for greatly reducing patient dose by inserting an attenuator with an aperture into the x-ray beam. The aperture defines an ROI with normal dose and image quality, while under the attenuator the dose and quality are reduced. A moveable copper ROI attenuator has been installed in the collimator assembly of a Toshiba Infinix system. The DTS provides a 3D-dose mapping on a patient graphic and, to track dose for ROI fluoroscopy, the software now models the attenuator shape and position. A calibration file provides values for the transmission of the attenuator as a function of kVp and beam filtration and dose corrections are performed if a ray to a given point on the patient graphic is determined to intersect the attenuator. Backscatter is included in the skin-dose determination and is dependent on the ROI beam size projected onto the patient. In the current version, a spatially invariant factor corrects for backscatter within the ROI and from the ROI region into the attenuated region. The agreement of the dose distribution calculated by the DTS with the actual distribution was verified by measurement with calibrated radiochromic film and a 20-cm PMMA phantom. Results: The DTS is able to accurately model the size and position of the ROI attenuator as projected onto the patient graphic. Measurements with radiochromic film show the skin-dose estimation agreement to be within +/−12%, with most error arising from the spatial variation of backscatter. Conclusion: The dose distribution on the patient can now be tracked in real-time with acceptable accuracy when the new dose-saving feature of ROI fluoroscopy is used. This research was supported in part by Toshiba Medical Systems Corporation and NIH Grant R01EB002873.

Evaluation of a real-time display for skin dose map in cardiac catheterisation procedures.

The purpose of this work was to validate a prototype designed to display skin dose maps in real time for clinicians that perform interventional cardiology procedures. Measurements using copper absorbers and three kinds of dosemeters (solid-state, radiochromic film and optically stimulated luminescence) were performed in a catheterisation laboratory. Some clinical results are also discussed. The system provides patient skin doses with acceptable accuracy, taking into account couch shifts, wedge compensation filters and collimation. The greatest source of uncertainty is that resulting from patient shape modelling. From a set of 374 patients recorded, it can be concluded that the peak skin dose (PSD) for patients with the same cumulative air kerma at the patient entrance reference point can be rather different. This real-time skin dose calculator has resulted easier to manage for measuring patient PSDs than other methods based on films or CR plates. As well as an improvement for patient safety, it could prove a useful training tool for clinicians.

A Real-Time Skin Dose Tracking System for Biplane Neuro-Interventional Procedures.

A biplane dose-tracking system (Biplane-DTS) that provides a real-time display of the skin-dose distribution on a 3D-patient graphic during neuro-interventional fluoroscopic procedures was developed. Biplane-DTS calculates patient skin dose using geometry and exposure information for the two gantries of the imaging system acquired from the digital system bus. The dose is calculated for individual points on the patient graphic surface for each exposure pulse and cumulative dose for both x-ray tubes is displayed as color maps on a split screen showing frontal and lateral projections of a 3D-humanoid graphic. Overall peak skin dose (PSD), FOV-PSD and current dose rates for the two gantries are also displayed. Biplane-DTS uses calibration files of mR/mAs for the frontal and lateral tubes measured with and without the table in the beam at the entrance surface of a 20 cm thick PMMA phantom placed 15 cm tube-side of the isocenter. For neuro-imaging, conversion factors are applied as a function of entrance field area to scale the calculated dose to that measured with a Phantom Laboratory head phantom which contains a human skull to account for differences in backscatter between PMMA and the human head. The software incorporates inverse-square correction to each point on the skin and corrects for angulation of the beam through the table. Dose calculated by Biplane DTS and values measured by a 6-cc ionization chamber placed on the head phantom at multiple points agree within a range of -3% to +7% with a standard deviation for all points of less than 3%.

Patient skin dose measurements using a cable free system MOSFETs based in fluoroscopically guided percutaneous vertebroplasty, percutaneous disc decompression, radiofrequency medial branch neurolysis, and endovascular critical limb ischemia.

The purpose of this work has been to dosimetrically investigate four fluoroscopically guided interventions: the percutaneous vertebroplasty (PVP), the percutaneous disc decompression (PDD), the radiofrequency medial branch neurolysis (RF) (hereafter named spine procedures), and the endovascular treatment for the critical limb ischemia (CLI). The X‐ray equipment used was a Philips Integris Allura Xper FD20 imaging system provided with a dose‐area product (DAP) meter. The parameters investigated were: maximum skin dose (MSD), air kerma (Ka,r), DAP, and fluoroscopy time (FT). In order to measure the maximum skin dose, we employed a system based on MOSFET detectors. Before using the system on patients, a calibration factor Fc and correction factors for energy (CkV) and field size (CFD) dependence were determined. Ka,r, DAP, and FT were extrapolated from the X‐ray equipment. The analysis was carried out on 40 patients, 10 for each procedure. The average fluoroscopy time and DAP values were compared with the reference levels (RLs) proposed in literature. Finally, the correlations between MSD, FT, Ka,r, and DAP values, as well as between DAP and FT values, were studied in terms of Pearson's product‐moment coefficients for spine procedures only. An Fc value of 0.20 and a very low dependence of CFD on field size were found. A third‐order polynomial function was chosen for CkV. The mean values of MSD ranged from 2.3 to 10.8 cGy for CLI and PVP, respectively. For these procedures, the DAP and FT values were within the proposed RL values. The statistical analysis showed little correlation between the investigated parameters. The interventional procedures investigated were found to be both safe with regard to deterministic effects and optimized for stochastic ones. In the spine procedures, the observed correlations indicated that the estimation of MSD from Ka,r or DAP was not accurate and a direct measure of MSD is therefore recommended.PACS number: 87

Monitoring methods for skin dose in interventional radiology

Interventional radiology makes an increasing use of X-ray for diagnostic and therapeutic procedures. The dose received by the patient sometime exceeds the threshold value of deterministic effects, and this requires monitoring of the dose delivered to the patients. Delivered dose could be assessed through either direct or indirect methods. The direct methods use dosimeters that are placed on the skin during the procedure, whereas, the indirect methods are based on measured quantities derived from the equipment itself. Each method has its own limitations; however, the main concern is the ability to measure the dose more accurately due to complexity of the anatomical structures of the patient and the variable course of each procedure. This review article summarizes the principle and main advantages and disadvantages of each method. A comparison of the performances of each method for interventional fluoroscopy and radiography in its ability to monitor the patient's skin dose is provided.

Measurement of maximum skin dose in interventional radiology and cardiology and challenges in the set-up of European alert thresholds

To help operators acknowledge patient dose during interventional procedures, EURADOS WG-12 focused on measuring patient skin dose using XR-RV3 gafchromic films, thermoluminescent detector (TLD) pellets or 2D TL foils and on investigating possible correlation to the on-line dose indicators such as fluoroscopy time, Kerma-area product (KAP) and cumulative air Kerma at reference point (CK). The study aims at defining non-centre-specific European alert thresholds for skin dose in three interventional procedures: chemoembolization of the liver (CE), neuroembolization (NE) and percutaneous coronary interventions (PCI). Skin dose values of >3 Gy (ICRP threshold for skin injuries) were indeed measured in these procedures confirming the need for dose indicators that correlate with maximum skin dose (MSD). However, although MSD showed fairly good correlation with KAP and CK, several limitations were identified challenging the set-up of non-centre-specific European alert thresholds. This paper presents preliminary results of this wide European measurement campaign and focuses on the main challenges in the definition of European alert thresholds.

SU‐E‐CAMPUS‐I‐04: Automatic Skin‐Dose Mapping for An Angiographic System with a Region‐Of‐Interest, High‐Resolution Detector

Purpose:Our real‐time skin dose tracking system (DTS) has been upgraded to monitor dose for the micro‐angiographic fluoroscope (MAF), a high‐resolution, small field‐of‐view x‐ray detector.Methods:The MAF has been mounted on a changer on a clinical C‐Arm gantry so it can be used interchangeably with the standard flat‐panel detector (FPD) during neuro‐interventional procedures when high resolution is needed in a region‐of‐interest. To monitor patient skin dose when using the MAF, our DTS has been modified to automatically account for the change in scatter for the very small MAF FOV and to provide separated dose distributions for each detector. The DTS is able to provide a color‐coded mapping of the cumulative skin dose on a 3D graphic model of the patient. To determine the correct entrance skin exposure to be applied by the DTS, a correction factor was determined by measuring the exposure at the entrance surface of a skull phantom with an ionization chamber as a function of entrance beam size for various beam filters and kVps. Entrance exposure measurements included primary radiation, patient backscatter and table forward scatter. To allow separation of the dose from each detector, a parameter log is kept that allows a replay of the procedure exposure events and recalculation of the dose components. The graphic display can then be constructed showing the dose distribution from the MAF and FPD separately or together.Results:The DTS is able to provide separate displays of dose for the MAF and FPD with field‐size specific scatter corrections. These measured corrections change from about 49% down to 10% when changing from the FPD to the MAF.Conclusion:The upgraded DTS allows identification of the patient skin dose delivered when using each detector in order to achieve improved dose management as well as to facilitate peak skin‐dose reduction through dose spreading.Research supported in part by Toshiba Medical Systems Corporation and NIH Grants R43FD0158401, R44FD0158402 and R01EB002873

SU-E-T-541: Bolus Effect of Thermoplastic Masks in IMRT and VMAT Head and Neck Treatments

Purpose: To quantitatively evaluate the bolus effect of thermoplalstic mask on patient skin dose during multi-field IMRT and VMAT treatment. Methods: The clinically approved target contours for five head and neck patients were deformably registered to an anthropomorphic Rando phantom. Two plans: Multifield IMRT plan with 7-9 beams and VMAT plan with 2-4 arcs were created for each patient following same dose constraints. 3mm skin was excluded from PTVs but not constrained during optimization. The prescription dose was 200-220 cGy/fraction. A thermoplastic head and shoulder mask was customized for the Rando phantom. Each plan was delivered to the phantom twice with and without mask. During each delivery, two rectangular strips of EBT3 films (1cm x 6.8cm) were placed across the anterior upper and lower neck near PTVs to measure the surface dose. For consistency films were positioned at same locations for same patient. A total of 8 film strips were obtained for each patient. Film dose was calibrated in the range of 0-400cGy on the day of plan delivery. For dose comparison 3 regions of interests (ROIs) of 1×1 cm2 were selected at left, right and middle part of each film, resulting in 6 point doses at each plan delivery. Results: The films without mask show relatively uniform dose distribution while those with mask clearly show mesh pattern of mask, usually indicating an increase in skin dose. On average the increase in skin dose over all ROIs with mask was 31.9%(±14.8%) with a range of 11.4%- 58.4%. There is no statistically significant difference (p=0.44) between skin dose increase in VMAT (30.8%±15.3%) and IMRT delivery (33.0%±14.9%). Conclusion: Thermoplastic immobilization masks increase surface dose for HN patient by around 30%. The magnitude is comparable between multi-field IMRT and VMAT. Radiochromic EBT3 film serves as an effective tool to quantify bolus effect.

SU‐E‐J‐36: Combining CBCT Dose Into IMRT Treatment Planning

Purpose:Cone beam CT (CBCT) is increasingly used in patient setup for IMRT. Daily CBCT may provide effective localization, however, it introduces concern over excessive imaging dose. Previous studies investigated the calculation of excess CBCT dose, however, no study has yet treated this dose as a source of therapeutic radiation, optimized in consideration of PTV and OARs constrains. Here we present a novel combined MV+kV inverse optimization engine to weave the CBCT and MV dose together such that CBCT dose is used for both imaging and therapeutic purposes. This may mitigate some of the excess imaging dose effects of daily CBCT and allow complete evaluation of the CBCT dose prior to treatment.Methods:The EGSnrc Monte Carlo system was used to model a Varian Trilogy CBCT system and 6 MV treatment beam. Using the model, the dose to patient from treatment beam and imaging beam was calculated for ten patients. The standard IMRT objective function was modified to include CBCT dose. Treatment plan optimization using the MOSEK optimization tool was performed retrospectively with and without assuming kV radiation dose from CBCT, assuming one CBCT per fraction.Results:Across ten patients, the CBCT delivered peaks of between .4% and 3.0% of the prescription dose to the PTV, with average CBCT dose to the PTV between .3% and .8%. By including CBCT dose to skin as a constraint during optimization, peak skin dose is reduced by between 1.9% and 7.4%, and average skin dose is reduced by .2% to 3.3%.Conclusions:Pre‐treatment CBCT may deliver a substantial amount of radiation dose to the target volume. By considering CBCT dose to skin at the point of treatment planning, it is possible to reduce patient skin dose from current clinical levels, and to provide patient treatment with the improved accuracy that daily CBCT provides.

Intercomparison of Gafchromic™ films, TL detectors and TL foils for the measurements of skin dose in interventional radiology

Several passive solid state dosemeters, such as Gafchromic™ films and thermoluminescence (TL) detectors, are used to estimate and monitor patient skin doses in interventional radiology. To determine the suitability of XR-TypeR Gafchromic™ films and of detectors based on TL materials: pellets, chips and foils to measure skin dose, an intercomparison exercise has been organized within European Dosimetry Radiation Group – Working Group 12 “European Medical ALARA Network” (EURADOS WG12). To test response detectors were exposed to X-ray beams of energies and qualities applied clinically. A blind test was also performed to investigate the accuracy of the dose estimate by detectors exposed to unknown doses. We found the response of films to be strongly dependent on beam quality and filtration (increasing by up to 80% with respect to reference beam quality). The response of TL detectors was found to be less dependent on beam quality (less than 25% variation), with TL foils showing less than 10% variation with respect to reference beam quality. To accurately estimate patient skin doses in interventional radiology it is important to choose the quality of the calibration beam to be as close as possible to the quality of beams actually applied in clinical work.

In vivo and phantom measurements versus Eclipse TPS prediction of near surface dose for SBRT treatments

This study reports on Gafchromic EBT2 film skin dose measurements for lung stereotactic body radiotherapy. These measurements were compared to near surface skin doses predicted by Eclipse treatment planning system (TPS) using the Analytical Anisotropic Algorithm (AAA) for a 6 MV photon beam. The accuracy of the predicted near surface dose for 3×3, 5×5 and 10×10 cm2 fields was assessed using an Attix chamber and EBT2 film in a Virtual Water phantom and compared to Monte Carlo calculation. The maximum near surface dose and its location were identified from the patient's treatment plan. For phantom measurements, the TPS dose (nominal 0 mm depth) was higher than the Attix chamber data by up to 24.0 % but in closer agreement with the EBT2 film measurement, which was up to 10.3 % higher than the Attix data. The MC calculated dose values were higher than the Attix data by up to 3.5% for the depths up to 2 mm. The maximum patient skin dose estimated from in vivo EBT2 film measurements was 7.5 – 19.5 Gy per course and depended on the number of overlapping fields, beam weight and/or contact with immobilisation devices. The TPS predicted dose for patient plans was mostly higher than the in vivo dose, by as much as 69.3%, but in two cases was lower, by as much as -23.1%.

Total skin electron beam irradiation in Greece: in-vivo dosimetry

Total skin electron beam irradiation in Greece: in-vivo dosimetry

Latest-generation catheterization systems enable invasive submillisievert coronary angiography

The radiation risk of patients undergoing invasive cardiology remains considerable and includes skin injuries and cancer. To date, submillisievert coronary angiography has not been considered feasible. In 2011, we compared results from 100 consecutive patients undergoing elective coronary angiography using the latest-generation flat-panel angiography system (FPS) with results from examinations by the same operator using 106 historic controls with a conventional image-intensifier system (IIS) that was new in 2002. The median patient exposure parameters were measured as follows: dose-area product (DAP) associated with radiographic cine acquisitions (DAP(R)) and fluoroscopy (DAP(F)) scenes, radiographic frames and runs, and cumulative exposure times for radiography and fluoroscopy. On the FPS as compared to the traditional IIS, radiographic detector entrance dose levels were reduced from 164 to 80 nGy/frame and pulse rates were lowered from 12.5/s to 7.5/s during radiography and from 25/s to 4/s during fluoroscopy. The cardiologist's performance patterns remained comparable over the years: fluoroscopy time was constant and radiography time even slightly increased. Overall patient DAP decreased from 7.0 to 2.4 Gy × cm(2); DAP(R), from 4.2 to 1.7 Gy × cm(2); and DAP(F), from 2.8 to 0.6 Gy × cm(2). Time-adjusted DAP(R)/s decreased from 436 to 130 mGy × cm(2) and DAP(F)/s, from 21.6 to 4.4 mGy × cm(2). Cumulative patient skin dose with the FPS amounted to 67 mGy, and the median (interquartile range) of effective dose was 0.5 (0.3 … 0.7) mSv. Consistent application of radiation-reducing techniques with the latest-generation flat-panel systems enables submillisievert coronary angiography in invasive cardiology.

SU‐E‐I‐28: Assessment of Maximum Patient Skin Dose for Interventional Radiology Procedures: Method and Uncertainty Analysis

Purpose: To develop a method for the assessment of patient's maximum skin dose in interventional radiology procedures. Methods: In the framework of EURADOS WG12, a European measurement protocol was developed to determine fluoroscopy patient skin dose for interventional procedures. The method investigates the use of XR‐RV3 gafchromic films, punctual TLDs and TLD sheets to intercept the X‐ray beam and measure the maximum skin dose. Beside investigating the optimal detector positioning, the method also looks for the most appropriate reading equipments and process (post‐exposure time analysis, projection vs. transmission scanning, etc.), calibration conditions (backscattering conditions, beam qualities etc.) and fitting procedure (inversely proportional to dose vs. traditionally‐used polynomials) based on a careful uncertainty investigation, Finally, the different dosemters are compared to establish the most practical and efficient method for clinical practice. Results: XR‐RV3 films, being large area dosemeters, proved to reproduce with good accuracy the dose distribution over the patient skin. Nonetheless, significant dependence with beam energy and quality, reading and fitting process was observed, which introduces important uncertainties in maximum skin dose measurement. Meanwhile, TLDs enabled precise dose estimates with lower uncertainty values but point TLD detectors may implicate missing the maximum dose location on the patient skin. Thus, TLD sheets could represent the most adapted tool for the assessment of fluoroscopy‐induced skin doses. However, nowadays, these are used only in few laboratories and remain inaccessible in clinical practice. The given recommendation on calibration, reading, fitting and data analysis will help Medical Physicists to conduct accurate dose assessments and optimize the radiation protection of the patient. Conclusion: The developed protocol standardizes practices of patient skin dose estimates in interventional radiology. Based on these results, the assessment, at European level, of alerts for interventional procedures using real‐time Kerma‐Area Product and Cumulative Air Kerma as skin dose indicators will be carried out. Research funded in the framework of EURADOS WG12. No disclosures, no conflict of interest.

TU‐A‐116‐09: Real‐Time Plastic Scintillation Dosimeter for Fluoroscopically‐Guided Interventional Procedures

Purpose: To monitor and measure, in real‐time, patient skin dose during fluoroscopically‐guided interventional (FGI) procedures using a novel plastic scintillation dosimeter (PSD). Methods: A clear optical fiber of 1 mm diameter, 10 m long, is optically coupled to a plastic scintillation fiber (BCF‐60) of 1 mm diameter, 10 mm long. On its other end, the clear fiber is connected to an avalanche photodiode, APD (C4777‐01, Hamamatsu). An electrometer collects the APD charge and displays live graph and dose values. Initial calibration is achieved with a NRC calibrated Farmer‐type ionization chamber (Exradin A12, Standard Imaging). The PSD and the chamber are set on an Allura Xper Fd10/10 (Philips) intervention table at the Air Kerma reference point, 150 mm below isocentre. In compliance with TG‐125 data collection methodology, slabs of solid water are gradually added over the instruments. In order to preserve image quality, the automatic controls increase tube current and kVp accordingly. Acquisitions are made in both cine‐fluorography and fluoroscopy operation modes, at 15 frames/s. Measurements were repeated by replacing the solid water by an Alderson RANDO phantom, with image intensifier as close as possible of the surface to replicate clinical protocols. Results: The calibration curves indicate that PSD response is linear below 80 kVp, but exhibits a quadratic behavior above, with a rate of 20–40 pA/mGy over Air Kerma Rate range of 0.10–16 mGy/s. The PSD can read dose rate as low as 1.7 mGy/s ± 5 %. However, uncertainties rise above 10 % for dose rate less than 1 mGy/s. Phantom measurements indicate that the dosimeter is accurate for clinical applications. Conclusion: A PSD has been calibrated and tested in order to monitor and measure low dose rates involved in FGI procedures in real‐time. The next steps will include Monte Carlo calculations to assess accuracy before starting clinical procedures.

MO‐A‐WAB‐01: MRI‐Guided Radiation Therapy

The concept of integrating a magnetic resonance imaging (MRI) scanner with a therapy radiation source, either a therapy linear accelerator (linac) or 60 Co, emerged as a feasible novel approach for MRI‐guided radiation therapy (i.e. MRIgRT or MRgRT) in recent years. The main motivation for the technological development of such radiotherapy systems is to provide state of the art MR imaging inside the treatment room to guide the treatment delivery. MRI offers the capability to visualize soft‐tissue as well as to perform physiological assessment of healthy and tumor tissues. The aim of MRIgRT is to facilitate adaptive radiotherapy by using on demand MRI data to update and personalize patient treatments.The MRI‐linac/ 60 Co system integration is a challenging task due to the intrinsic default incompatibility between the sub‐components. Multiple interdependent issues need to be resolved in order to achieve the optimal operation of the MRI scanner and the radiation source(s) such as: a) radiofrequency (RF) interference, b) magnetic field coupling, c) perturbation of the dose deposited in tissue due to the presence of an external magnetic field, and d) escalation of patient skin dose. This translates into solving a complex optimization problem which drives the overall system architecture. The session will provide an overview of the MRI‐guided radiation therapy systems. The speakers will present the specifics of their proposed designs and the latest technological developments (hardware and software). They will also discuss key aspects related to the clinical implementation of their systems such as safety, applications, workflows, quality control, staffing models for supporting the infrastructure, and preliminary data.Learning Objectives:1. Understand the main concepts of MRI‐guided radiation therapy;2. Understand the issues and proposed solutions related to the integration of MRI‐guided radiotherapy systems;3. Understand the advantages and limitations of MRI‐guided radiotherapy systems.